Lincoln Electric Power Mig 255 Svm144 B Users Manual

SVM144-B to the manual 4004c637-834f-4269-b98d-a225789a81fc

2015-02-09

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SVM144-B
July, 2006

POWER MIG 255
For use with machines having Code Number : 10563, 10583,10986, 10990

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Safety Depends on You

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Lincoln arc welding and cutting
equipment is designed and built
with safety in mind. However,
your overall safety can be
increased by proper installation
. . . and thoughtful operation on
your part. DO NOT INSTALL,
OPERATE OR REPAIR THIS
EQUIPMENT WITHOUT READING THIS MANUAL AND THE
SAFETY PRECAUTIONS CONTAINED THROUGHOUT. And,
most importantly, think before
you act and be careful.

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SERVICE MANUAL

• World's Leader in Welding and Cutting Products •
• Sales and Service through Subsidiaries and Distributors Worldwide •

Cleveland, Ohio 44117-1199 U.S.A. TEL: 216.481.8100 FAX: 216.486.1751 WEB SITE: www.lincolnelectric.com

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SAFETY

WARNING
CALIFORNIA PROPOSITION 65 WARNINGS
Diesel engine exhaust and some of its constituents
are known to the State of California to cause cancer, birth defects, and other reproductive harm.
The Above For Diesel Engines

The engine exhaust from this product contains
chemicals known to the State of California to cause
cancer, birth defects, or other reproductive harm.
The Above For Gasoline Engines

ARC WELDING CAN BE HAZARDOUS. PROTECT YOURSELF AND OTHERS FROM POSSIBLE SERIOUS INJURY OR DEATH.
KEEP CHILDREN AWAY. PACEMAKER WEARERS SHOULD CONSULT WITH THEIR DOCTOR BEFORE OPERATING.

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Read and understand the following safety highlights. For additional safety information, it is strongly recommended that you
purchase a copy of “Safety in Welding & Cutting - ANSI Standard Z49.1” from the American Welding Society, P.O. Box 351040,
Miami, Florida 33135 or CSA Standard W117.2-1974. A Free copy of “Arc Welding Safety” booklet E205 is available from the
Lincoln Electric Company, 22801 St. Clair Avenue, Cleveland, Ohio 44117-1199.

BE SURE THAT ALL INSTALLATION, OPERATION, MAINTENANCE AND REPAIR PROCEDURES ARE
PERFORMED ONLY BY QUALIFIED INDIVIDUALS.

FOR ENGINE
powered equipment.

1.h. To avoid scalding, do not remove the
radiator pressure cap when the engine is
hot.

1.a. Turn the engine off before troubleshooting and maintenance
work unless the maintenance work requires it to be running.
____________________________________________________
1.b. Operate engines in open, well-ventilated
areas or vent the engine exhaust fumes
outdoors.

____________________________________________________
1.c. Do not add the fuel near an open flame welding arc or when the engine is running. Stop
the engine and allow it to cool before refueling to prevent spilled fuel from vaporizing on
contact with hot engine parts and igniting. Do
not spill fuel when filling tank. If fuel is spilled,
wipe it up and do not start engine until fumes
have been eliminated.
____________________________________________________
1.d. Keep all equipment safety guards, covers and devices in position and in good repair.Keep hands, hair, clothing and tools
away from V-belts, gears, fans and all other moving parts
when starting, operating or repairing equipment.
____________________________________________________
1.e. In some cases it may be necessary to remove safety
guards to perform required maintenance. Remove
guards only when necessary and replace them when the
maintenance requiring their removal is complete.
Always use the greatest care when working near moving
parts.
___________________________________________________
1.f. Do not put your hands near the engine fan.
Do not attempt to override the governor or
idler by pushing on the throttle control rods
while the engine is running.

ELECTRIC AND
MAGNETIC FIELDS
may be dangerous
2.a. Electric current flowing through any conductor causes
localized Electric and Magnetic Fields (EMF). Welding
current creates EMF fields around welding cables and
welding machines
2.b. EMF fields may interfere with some pacemakers, and
welders having a pacemaker should consult their physician
before welding.
2.c. Exposure to EMF fields in welding may have other health
effects which are now not known.
2.d. All welders should use the following procedures in order to
minimize exposure to EMF fields from the welding circuit:
2.d.1. Route the electrode and work cables together - Secure
them with tape when possible.
2.d.2. Never coil the electrode lead around your body.
2.d.3. Do not place your body between the electrode and
work cables. If the electrode cable is on your right
side, the work cable should also be on your right side.
2.d.4. Connect the work cable to the workpiece as close as
possible to the area being welded.

___________________________________________________
1.g. To prevent accidentally starting gasoline engines while
turning the engine or welding generator during maintenance
work, disconnect the spark plug wires, distributor cap or
magneto wire as appropriate.

2.d.5. Do not work next to welding power source.

Mar ‘95

LN-15

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ELECTRIC SHOCK can kill.

ARC RAYS can burn.

3.a. The electrode and work (or ground) circuits
are electrically “hot” when the welder is on.
Do not touch these “hot” parts with your bare
skin or wet clothing. Wear dry, hole-free
gloves to insulate hands.

4.a. Use a shield with the proper filter and cover
plates to protect your eyes from sparks and
the rays of the arc when welding or observing
open arc welding. Headshield and filter lens
should conform to ANSI Z87. I standards.

3.b. Insulate yourself from work and ground using dry insulation.
Make certain the insulation is large enough to cover your full
area of physical contact with work and ground.

4.b. Use suitable clothing made from durable flame-resistant
material to protect your skin and that of your helpers from
the arc rays.

In addition to the normal safety precautions, if welding
must be performed under electrically hazardous
conditions (in damp locations or while wearing wet
clothing; on metal structures such as floors, gratings or
scaffolds; when in cramped positions such as sitting,
kneeling or lying, if there is a high risk of unavoidable or
accidental contact with the workpiece or ground) use
the following equipment:
• Semiautomatic DC Constant Voltage (Wire) Welder.
• DC Manual (Stick) Welder.
• AC Welder with Reduced Voltage Control.

4.c. Protect other nearby personnel with suitable, non-flammable
screening and/or warn them not to watch the arc nor expose
themselves to the arc rays or to hot spatter or metal.

FUMES AND GASES
can be dangerous.
5.a. Welding may produce fumes and gases
hazardous to health. Avoid breathing these
fumes and gases.When welding, keep
your head out of the fume. Use enough
ventilation and/or exhaust at the arc to keep
fumes and gases away from the breathing zone. When
welding with electrodes which require special
ventilation such as stainless or hard facing (see
instructions on container or MSDS) or on lead or
cadmium plated steel and other metals or coatings
which produce highly toxic fumes, keep exposure as
low as possible and below Threshold Limit Values (TLV)
using local exhaust or mechanical ventilation. In
confined spaces or in some circumstances, outdoors, a
respirator may be required. Additional precautions are
also required when welding on galvanized steel.

3.c. In semiautomatic or automatic wire welding, the electrode,
electrode reel, welding head, nozzle or semiautomatic
welding gun are also electrically “hot”.
3.d. Always be sure the work cable makes a good electrical
connection with the metal being welded. The connection
should be as close as possible to the area being welded.
3.e. Ground the work or metal to be welded to a good electrical
(earth) ground.
3.f. Maintain the electrode holder, work clamp, welding cable and
welding machine in good, safe operating condition. Replace
damaged insulation.

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SAFETY

3.g. Never dip the electrode in water for cooling.
3.h. Never simultaneously touch electrically “hot” parts of
electrode holders connected to two welders because voltage
between the two can be the total of the open circuit voltage
of both welders.
3.i. When working above floor level, use a safety belt to protect
yourself from a fall should you get a shock.
3.j. Also see Items 6.c. and 8.

5.b. Do not weld in locations near chlorinated hydrocarbon vapors
coming from degreasing, cleaning or spraying operations.
The heat and rays of the arc can react with solvent vapors to
form phosgene, a highly toxic gas, and other irritating products.
5.c. Shielding gases used for arc welding can displace air and
cause injury or death. Always use enough ventilation,
especially in confined areas, to insure breathing air is safe.
5.d. Read and understand the manufacturer’s instructions for this
equipment and the consumables to be used, including the
material safety data sheet (MSDS) and follow your
employer’s safety practices. MSDS forms are available from
your welding distributor or from the manufacturer.
5.e. Also see item 1.b.

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Mar ‘95

LN-15

SAFETY

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iii

WELDING SPARKS can
cause fire or explosion.
6.a. Remove fire hazards from the welding area.
If this is not possible, cover them to prevent
the welding sparks from starting a fire.
Remember that welding sparks and hot
materials from welding can easily go through small cracks
and openings to adjacent areas. Avoid welding near
hydraulic lines. Have a fire extinguisher readily available.
6.b. Where compressed gases are to be used at the job site,
special precautions should be used to prevent hazardous
situations. Refer to “Safety in Welding and Cutting” (ANSI
Standard Z49.1) and the operating information for the
equipment being used.

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6.c. When not welding, make certain no part of the electrode
circuit is touching the work or ground. Accidental contact can
cause overheating and create a fire hazard.
6.d. Do not heat, cut or weld tanks, drums or containers until the
proper steps have been taken to insure that such procedures
will not cause flammable or toxic vapors from substances
inside. They can cause an explosion even though they have
been “cleaned”. For information, purchase “Recommended
Safe Practices for the Preparation for Welding and Cutting of
Containers and Piping That Have Held Hazardous
Substances”, AWS F4.1 from the American Welding Society
(see address above).
6.e. Vent hollow castings or containers before heating, cutting or
welding. They may explode.
6.f. Sparks and spatter are thrown from the welding arc. Wear oil
free protective garments such as leather gloves, heavy shirt,
cuffless trousers, high shoes and a cap over your hair. Wear
ear plugs when welding out of position or in confined places.
Always wear safety glasses with side shields when in a
welding area.

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iii

6.g. Connect the work cable to the work as close to the welding
area as practical. Work cables connected to the building
framework or other locations away from the welding area
increase the possibility of the welding current passing
through lifting chains, crane cables or other alternate circuits.
This can create fire hazards or overheat lifting chains or
cables until they fail.
6.h. Also see item 1.c.

CYLINDER may explode
if damaged.
7.a. Use only compressed gas cylinders
containing the correct shielding gas for the
process used and properly operating
regulators designed for the gas and
pressure used. All hoses, fittings, etc. should be suitable for
the application and maintained in good condition.
7.b. Always keep cylinders in an upright position securely
chained to an undercarriage or fixed support.
7.c. Cylinders should be located:
• Away from areas where they may be struck or subjected to
physical damage.
• A safe distance from arc welding or cutting operations and
any other source of heat, sparks, or flame.
7.d. Never allow the electrode, electrode holder or any other
electrically “hot” parts to touch a cylinder.
7.e. Keep your head and face away from the cylinder valve outlet
when opening the cylinder valve.
7.f. Valve protection caps should always be in place and hand
tight except when the cylinder is in use or connected for
use.
7.g. Read and follow the instructions on compressed gas
cylinders, associated equipment, and CGA publication P-l,
“Precautions for Safe Handling of Compressed Gases in
Cylinders,” available from the Compressed Gas Association
1235 Jefferson Davis Highway, Arlington, VA 22202.

FOR ELECTRICALLY
powered equipment.
8.a. Turn off input power using the disconnect
switch at the fuse box before working on
the equipment.
8.b. Install equipment in accordance with the U.S. National
Electrical Code, all local codes and the manufacturer’s
recommendations.
8.c. Ground the equipment in accordance with the U.S. National
Electrical Code and the manufacturer’s recommendations.

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Mar ‘95

POWER MIG 255

SAFETY

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a. Les circuits à l’électrode et à la piéce sont sous tension
quand la machine à souder est en marche. Eviter toujours
tout contact entre les parties sous tension et la peau nue
ou les vétements mouillés. Porter des gants secs et sans
trous pour isoler les mains.
b. Faire trés attention de bien s’isoler de la masse quand on
soude dans des endroits humides, ou sur un plancher metallique ou des grilles metalliques, principalement dans
les positions assis ou couché pour lesquelles une grande
partie du corps peut être en contact avec la masse.
c. Maintenir le porte-électrode, la pince de masse, le câble de
soudage et la machine à souder en bon et sûr état defonctionnement.
d.Ne jamais plonger le porte-électrode dans l’eau pour le
refroidir.
e. Ne jamais toucher simultanément les parties sous tension
des porte-électrodes connectés à deux machines à souder
parce que la tension entre les deux pinces peut être le total
de la tension à vide des deux machines.
f. Si on utilise la machine à souder comme une source de
courant pour soudage semi-automatique, ces precautions
pour le porte-électrode s’applicuent aussi au pistolet de
soudage.

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Pour votre propre protection lire et observer toutes les instructions
et les précautions de sûreté specifiques qui parraissent dans ce
manuel aussi bien que les précautions de sûreté générales suivantes:

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PRÉCAUTIONS DE SÛRETÉ

Sûreté Pour Soudage A L’Arc
1. Protegez-vous contre la secousse électrique:

2. Dans le cas de travail au dessus du niveau du sol, se protéger
contre les chutes dans le cas ou on recoit un choc. Ne jamais
enrouler le câble-électrode autour de n’importe quelle partie du
corps.
3. Un coup d’arc peut être plus sévère qu’un coup de soliel, donc:

zones où l’on pique le laitier.
6. Eloigner les matériaux inflammables ou les recouvrir afin de
prévenir tout risque d’incendie dû aux étincelles.
7. Quand on ne soude pas, poser la pince à une endroit isolé de
la masse. Un court-circuit accidental peut provoquer un
échauffement et un risque d’incendie.
8. S’assurer que la masse est connectée le plus prés possible de
la zone de travail qu’il est pratique de le faire. Si on place la
masse sur la charpente de la construction ou d’autres endroits
éloignés de la zone de travail, on augmente le risque de voir
passer le courant de soudage par les chaines de levage,
câbles de grue, ou autres circuits. Cela peut provoquer des
risques d’incendie ou d’echauffement des chaines et des
câbles jusqu’à ce qu’ils se rompent.
9. Assurer une ventilation suffisante dans la zone de soudage.
Ceci est particuliérement important pour le soudage de tôles
galvanisées plombées, ou cadmiées ou tout autre métal qui
produit des fumeés toxiques.
10. Ne pas souder en présence de vapeurs de chlore provenant
d’opérations de dégraissage, nettoyage ou pistolage. La
chaleur ou les rayons de l’arc peuvent réagir avec les vapeurs
du solvant pour produire du phosgéne (gas fortement toxique)
ou autres produits irritants.
11. Pour obtenir de plus amples renseignements sur la sûreté, voir
le code “Code for safety in welding and cutting” CSA Standard
W 117.2-1974.

PRÉCAUTIONS DE SÛRETÉ POUR
LES MACHINES À SOUDER À
TRANSFORMATEUR ET À
REDRESSEUR

a. Utiliser un bon masque avec un verre filtrant approprié ainsi
qu’un verre blanc afin de se protéger les yeux du rayonnement de l’arc et des projections quand on soude ou
quand on regarde l’arc.
b. Porter des vêtements convenables afin de protéger la peau
de soudeur et des aides contre le rayonnement de l‘arc.
c. Protéger l’autre personnel travaillant à proximité au
soudage à l’aide d’écrans appropriés et non-inflammables.

1. Relier à la terre le chassis du poste conformement au code de
l’électricité et aux recommendations du fabricant. Le dispositif
de montage ou la piece à souder doit être branché à une
bonne mise à la terre.

4. Des gouttes de laitier en fusion sont émises de l’arc de
soudage. Se protéger avec des vêtements de protection libres
de l’huile, tels que les gants en cuir, chemise épaisse, pantalons sans revers, et chaussures montantes.

3. Avant de faires des travaux à l’interieur de poste, la debrancher à l’interrupteur à la boite de fusibles.

2. Autant que possible, I’installation et l’entretien du poste seront
effectués par un électricien qualifié.

4. Garder tous les couvercles et dispositifs de sûreté à leur place.

5. Toujours porter des lunettes de sécurité dans la zone de
soudage. Utiliser des lunettes avec écrans lateraux dans les

POWER MIG 255

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MASTER TABLE OF CONTENTS FOR ALL SECTIONS
Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

i-iv

Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Section A
Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Section B
Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Section C
Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Section D
Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Section E
Troubleshooting and Repair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Section F
Electrical Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Section G
Parts Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .P344 Series

POWER MIG 255

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Section A-1

TABLE OF CONTENTS
- INSTALLATION SECTION -

Section A-1

Installation ..............................................................................................................Section A

Technical Specifications...............................................................................................A-2
Safety Precautions .......................................................................................................A-3
Uncrating the POWER MIG 255...................................................................................A-3
Location........................................................................................................................A-3
Input Power, Grounding and Connection Diagrams ....................................................A-3

Gun and Cable Installation...........................................................................................A-6
Shielding Gas ...............................................................................................................A-6

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Output Polarity Connections........................................................................................A-5

INSTALLATION

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A-2

TECHNICAL SPECIFICATIONS – POWER MIG 255
INPUT – SINGLE PHASE ONLY
Standard Voltage/Frequency Input Current @ 200 Amp Rated Output Input Current @ 250 Amp Rated Output
208/230/60 Hz
41/37 Amps
50/46
230/460/575/60 Hz
41/20/16 Amps
50/24/19

RATED OUTPUT
Duty Cycle
40%
60%
100%

Amps
250 Amps
200 Amps
145 Amps

Volts at Rated Amperes
26 Volts
28 Volts
26 Volts

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OUTPUT
Welding Current Range
(Continuous)
30 – 300 Amps

Maximum Open Circuit Voltage

Welding Voltage Range

40 Volts

10-28 Volts

RECOMMENDED INPUT WIRE AND FUSE SIZES

Input Voltage/
Frequency (Hz)

Fuse or Breaker
Size (Super Lag)

Input Ampere
Rating On
Nameplate

208/60
230/60
460/60
575/60

60
60
30
25

50
46
24
19

75°C Copper Wire
in Conduit
AWG (IEC) Sizes
(For lengths
up to 100 ft)
8 (10 mm2)
10 (6 mm2)
14 (2.5 mm2)
14 (2.5 mm2)

75°C Copper Wire
in Conduit
AWG (IEC) Sizes
(For lengths
exceeding 100 ft)
6 (16 mm2)
8 (10 mm2)
12 (4 mm2)
12 (4 mm2)

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NOTE: Use #10 AWG Grounding Wire

PHYSICAL DIMENSIONS
Height
31.79 in.
808 mm

Width
18.88 in.
480 mm

Depth
38.78 in.
985 mm

Weight
220 Ibs
100 kg

WIRE SPEED RANGE
Wire Speed

50 – 700 IPM (1.27 – 17.8 m/minute)

POWER MIG 255

INSTALLATION

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A-3

Read entire installation section before starting
installation.

INPUT POWER, GROUNDING AND
CONNECTION DIAGRAMS

SAFETY PRECAUTIONS
WARNING
WARNING

ELECTRIC SHOCK can kill.
• Do not touch electrically live parts such as
output terminals or internal wiring.

ELECTRIC SHOCK can kill.
• Only qualified personnel should perform this
installation.
• Only personnel that have read and understood the POWER MIG 255 Operating
Manual should install and operate this equipment.

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• Machine must be grounded per any national,
local or other applicable electrical codes.

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A-3

• The POWER MIG power switch is to be in the
OFF position when installing work cable and
gun and when connecting other equipment.

------------------------------------------------------------------------

UNCRATING THE POWER MIG 255
Cut banding and lift off cardboard carton. Cut banding
holding the machine to the skid. Remove foam and corrugated packing material. Untape accessories from
Gas Bottle Platform. Unscrew the two wood screws (at
the Gas Bottle Platform) holding the machine to the
skid. Roll the machine off the skid assembly.

• All input power must be electrically disconnected before proceeding.

-----------------------------------------------------------------------1. Before starting the installation, check with the
local power company if there is any question
about whether your power supply is adequate for
the voltage, amperes, phase, and frequency specified on the welder nameplate. Also be sure the
planned installation will meet the U.S. National
Electrical Code and local code requirements. This
welder may be operated from a single phase line
or from one phase of a two or three phase line.
2. Models that have multiple input voltages specified
on the nameplate (e.g. 208/230) are shipped connected for the highest voltage. If the welder is to
be operated on lower voltage, it must be reconnected according to the instructions in Figure A.1
for dual voltage machines and Figure A.2 for
triple voltage machines.

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WARNING
LOCATION
Locate the welder in a dry location where there is free
circulation of clean air into the louvers in the back and
out the front. A location that minimizes the amount of
smoke and dirt drawn into the rear louvers reduces the
chance of dirt accumulation that can block air passages and cause overheating.

Make certain that the input power is electrically
disconnected before removing the screw on the
reconnect panel access cover.
------------------------------------------------------------------------

POWER MIG 255

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A-4

INSTALLATION

A-4

FIGURE A.1 — DUAL VOLTAGE MACHINE INPUT CONNECTIONS.

3. The 208/230 volt 60 Hz model POWER MIG is
shipped with a 10 ft. input cable and plug connected to the welder. A matching receptacle is
supplied with the machine. Mount the receptacle
in a suitable location using the screws provided.
Be sure it can be reached by the plug on the input
cable attached to the welder. Mount with the
grounding terminal at the top to allow the power
cable to hang down without bending.
The 230/460/575 volt 60 Hz model is not
equipped with a plug, an input cable, or a
receptacle.

4. Using the instructions in Figure A.3, have a qualified electrician connect the receptacle or cable to
the input power lines and the system ground per
the U.S. National Electrical Code and any applicable local codes. See Technical Specifications
at the beginning of this chapter for proper wire
sizes. For long runs over 100 feet, larger copper
wires should be used. Fuse the two hot lines with
super lag type fuses as shown in the following diagram. The center contact in the receptacle is for
the grounding connection. A green wire in the
input cable connects this contact to the frame of
the welder. This ensures proper grounding of the
welder frame when the welder plug is inserted into
the receptacle.

POWER MIG 255

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A-5

INSTALLATION
FIGURE A.2 — TRIPLE VOLTAGE MACHINE INPUT CONNECTIONS.

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FIGURE A.3 — RECEPTACLE DIAGRAM.

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A-5

CONNECT TO A SYSTEM
GROUNDING WIRE. SEE
THE UNITED STATES
NATIONAL ELECTRICAL
CODE AND/OR LOCAL
CODES FOR OTHER
DETAILS AND MEANS FOR
PROPER GROUNDING.
CONNECT TO HOT WIRES
OF A THREE-WIRE, SINGLE
PHASE SYSTEM OR TO ONE
PHASE OF A TWO OR
THREE PHASE SYSTEM.

OUTPUT POLARITY CONNECTIONS
The welder, as shipped from the factory, is connected
for electrode positive (+) polarity. This is the normal
polarity for GMA welding.
If negative (–) polarity is required, interchange the connection of the two cables located in the wire drive compartment near the front panel. The electrode cable,
which is attached to the wire drive, is to be connected
to the negative (–) labeled terminal. The work lead,
which is attached to the work clamp, is to be connected to the positive (+) labeled terminal.

POWER MIG 255

INSTALLATION

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A-6

GUN AND CABLE INSTALLATION

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2. Unscrew knurled screw on the drive unit front end
(inside wire feed compartment) until tip of screw
no longer protrudes into gun opening as seen
from front of machine.
3. Insert the male end of gun cable into the female
casting through opening in front panel. Make sure
connector is fully inserted and tighten knurled
screw.

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4. Connect the gun trigger connector from the gun
and cable to the mating receptacle inside the
compartment located above the gun connection
made in item 3 above. Make sure that the keyways are aligned, insert and tighten retaining ring.
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CYLINDER may explode if
damaged.
• Gas under pressure is explosive. Always keep
gas cylinders in an upright position and always
keep chained to undercarriage or stationary
support. See American National Standard Z49.1, “Safety in Welding and Cutting” published by the American Welding Society.

WARNING

1. Lay the cable out straight.

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WARNING

The Magnum 250L gun and cable provided with the
POWER MIG 255 is factory installed with a liner for
0.035-0.045 in. (0.9-1.2 mm) electrode and an 0.035
in. (0.9 mm) contact tip. Install the 0.045 tip (also provided) if this wire size is being used.

Turn the welder power switch off before installing
gun and cable.
------------------------------------------------------------------------

SHIELDING GAS

A-6

-----------------------------------------------------------------------3. Stand to one side away from the outlet and open
the cylinder valve for an instant. This blows away
any dust or dirt which may have accumulated in
the valve outlet.

WARNING
Be sure to keep your face away from the valve outlet when “cracking” the valve.
-----------------------------------------------------------------------4. Attach the flow regulator to the cylinder valve and
tighten the union nut(s) securely with a wrench.
NOTE: If connecting to 100% CO2 cylinder, insert
regulator adapter between regulator and cylinder
valve. If adapter is equipped with a plastic washer, be
sure it is seated for connection to the CO2 cylinder.
5. Attach one end of the inlet gas hose to the outlet
fitting of the flow regulator, the other end to the
POWER MIG 255 rear fitting, and tighten the
union nuts securely with a wrench.

(For Gas Metal Arc Welding Processes)
Customer must provide cylinder of appropriate type
shielding gas for the process being used.
A gas flow regulator, for CO2 or Argon blend gas, and
an inlet gas hose are factory provided with the POWER
MIG 255. Install the shielding gas supply as follows:
1. Set gas cylinder on rear platform of POWER MIG
255. Hook chain in place to secure cylinder to rear
of welder.
2. Remove the cylinder cap. Inspect the cylinder
valves and regulator for damaged threads, dirt,
dust, oil or grease. Remove dust and dirt with a
clean cloth.
DO NOT ATTACH THE REGULATOR IF OIL,
GREASE OR DAMAGE IS PRESENT! Inform
your gas supplier of this condition. Oil or grease
in the presence of high pressure oxygen is
explosive.

6. Before opening the cylinder valve, turn the regulator adjusting knob counterclockwise until the
adjusting spring pressure is released.
7. Standing to one side, open the cylinder valve
slowly a fraction of a turn. When the cylinder pressure gauge pointer stops moving, open the valve
fully.

WARNING
Never stand directly in front of or behind the flow
regulator when opening the cylinder valve. Always
stand to one side.
-----------------------------------------------------------------------8. The flow regulator is adjustable. Adjust it to the
flow rate recommended for the procedure and
process being used before making the weld.

POWER MIG 255

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Section B-1

TABLE OF CONTENTS
- OPERATION SECTION -

Section B-1

Operation ................................................................................................................Section B

Product Description......................................................................................................B-3
Recommended Processes and Equipment..................................................................B-3
Welding Capability........................................................................................................B-3
Limitations ....................................................................................................................B-3
Description of Controls ................................................................................................B-4

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Wire Drive Roll ..............................................................................................................B-4
Wire Size Conversion Parts..........................................................................................B-4
Procedure for Changing Drive and Idle Roll Sets ........................................................B-5
Wire Reel Loading - Readi-Reels, Spools, or Coils .....................................................B-5
To Mount a 30 lb (14 kg) Readi-Reel Package
(Using the Molded Plastic K363-P Readi-Reel Adapter).......................................B-5
To Mount 10 to 44 lb (4.5-20 kg) Spools (12 in./300 mm Diameter)
or 14 lb (6 kg) Innershield Coils .............................................................................B-5
To Start the Welder.......................................................................................................B-6
Feeding Wire Electrode ................................................................................................B-6
Idle Roll Pressure Setting .............................................................................................B-6

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Setting Run-In Speed on Standard Power MIG Feeder ..............................................B-6
Fast or Slow Run-In Mode Selection (When Timer Option is not Installed)..........B-6
Instructions to Enter Slow Run-In..........................................................................B-6
Instructions to Enter Fast Run-In...........................................................................B-6
Making a Weld..............................................................................................................B-7
Avoiding Wire Feeding Problems .................................................................................B-7
Fan Control...................................................................................................................B-8
Input Line Voltage Protection .......................................................................................B-8
Wire Feed Overload Protection ....................................................................................B-8
Welding Thermal Overload Protection .........................................................................B-8

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Overcurrent Protection .................................................................................................B-8

POWER MIG 255

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B-2

OPERATION
Read entire Operation section before
operating the POWER MIG 255.

WARNING
ELECTRIC SHOCK can kill.
• Do not touch electrically live parts
or electrode with skin or wet
clothing. Insulate yourself from
work and ground.

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• Always
gloves.

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B-2

wear

dry

insulating

FUMES AND GASES can be
dangerous.
• Keep your head out of fumes.
• Use ventilation or exhaust to
remove fumes from breathing
zone.

WELDING
SPARKS
can
cause fire or explosion.
• Keep flammable material away.

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• Do not weld on closed containers.

ARC RAYS can burn eyes and
skin.
• Wear eye, ear and body protection.

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Observe all safety information throughout
this manual.

POWER MIG 255

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B-3

OPERATION

PRODUCT DESCRIPTION
The POWER MIG™ 255 is a complete semiautomatic
constant voltage DC arc welding machine built to meet
NEMA specifications. It combines a constant voltage
power source and a constant speed wire feeder with a
microcomputer-based controller to form a reliable highperformance welding system. A simple control scheme,
consisting of continuous full range voltage and wire
feed speed controls, provides versatility with ease of
use and accuracy.
Other features include a 2 in. (51 mm) O.D. wire reel
spindle with adjustable brake, an integral gas cylinder
mounting undercarriage, an adjustable CO2 or Argon
blend flow regulator with cylinder pressure gauge and
inlet hose, a 12 ft (3.6 m) Magnum 250L GMAW gun
and cable with fixed (flush) nozzle, a 10 ft (3.0 m)
power cable with plug and mating receptacle, and a 10
ft (3.0 m) work cable with clamp.
An Optional Timer kit provides variable burnback control, a spot function, a selectable 4-step trigger interlock and adjustable “Run In” for wire starting optimization. Also optional are a Spool Gun Adapter kit, a Dual
Cylinder Mounting Kit and an Aluminum Feeding Kit for
push feeding with standard built in feeder.

B-3

RECOMMENDED PROCESSES
AND EQUIPMENT
The POWER MIG 255 is recommended for GMA
welding processes using 10 to 44 lb (4.5 to 20 kg)
2 in. (51 mm) I.D. spools or Readi-Reel® coils (with
optional adapter) of 0.025 in. through 0.045 in.
(0.6 to 1.2 mm) solid steel, 0.035 in. (0.9 mm)
stainless, 3/64 in. (1.2 mm) aluminum and 0.045 in.
(1.2 mm) Outershield®; as well as 0.035 in. (0.9 mm)
and 0.045 in. (1.2 mm) Innershield ® self-shielding
electrodes.
The POWER MIG is factory equipped to feed
0.035 in. (0.9 mm) electrodes and provides tip, guide,
and drive rolls for 0.045 in. (1.2 mm) electrode. It also
includes a 200A, 60% duty cycle (or 250A, 40% duty
cycle) rated, 12 ft (3.6 m) GMAW gun and cable
assembly equipped for these wire sizes. Use of GMAW
processes requires a supply of shielding gas.

WELDING CAPABILITY
The POWER MIG 255 is rated at 250 amps @ 26 volts,
at a 40% duty cycle based on a ten minute cycle time.
It is capable of higher duty cycles at lower output currents and capable of up to 300 Amps at lower duty
cycles.

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LIMITATIONS
The POWER MIG 255 MAY NOT operate
satisfactorily if powered with a portable or in-plant
generating system.

POWER MIG 255

OPERATION

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B-4

DESCRIPTION OF CONTROLS

WIRE DRIVE ROLL

Power ON/OFF Switch — Place the lever in the “ON”
position to energize the POWER MIG 255. When the
power is on, the red LED display lights illuminate.

The drive rolls installed with the POWER MIG each
have two grooves, both for 0.030-0.0035 in.
(0.8-0.9 mm) solid steel electrode. Drive roll size is indicated by the stencilling on the exposed side of the drive
roll. If feeding problems occur, then the drive roll may
be reversed or changed. See Procedure for
Changing Drive Roll in this section. This information
also appears on the Procedure Decal on the door
inside the wire compartment. An additional drive roll set
is provided for 0.045 in. (1.2 mm) solid steel electrode,
packaged standard with each machine.

Voltage Control — This is a continuous control that
gives full range adjustment of power source output voltage. It can be adjusted while welding over its 10 to 28
volt range.
Wire Speed Control — This controls the wire feed
speed from 50 to 700 inches per minute (1.2 to
17.8 m/min). The wire speed control can be preset on
the dial to the setting specified on the Procedure Decal
located inside the wire compartment door. Wire speed
is not affected when changes are made in the voltage
control.

WIRE SIZE CONVERSION PARTS
The POWER MIG 255 is rated to feed 0.025 through
0.045 in. (0.6 to 1.2 mm) solid or cored electrode sizes.
The drive roll kits and Magnum 250L gun and cable
parts are available to feed different sizes and types of
electrodes. See Accessories section.

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FIGURE B.1 — OPERATOR CONTROLS

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B-4

WIRE SPEED

VOLTS

LINCOLN

ELECTRIC

OFF

POWER MIG 255

POWER

POWER MIG 255

OPERATION

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B-5

PROCEDURE FOR CHANGING
DRIVE AND IDLE ROLL SETS

2 IN. O.D.
SPINDLE

1. Turn off the power source.
2. Release the pressure on the idle roll by swinging
the adjustable pressure arm down toward the
back of the machine. Lift the cast idle roll assembly and allow it to sit in an upright position.

BRAKE
HOLDING
PIN

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5. Wiggle both the metal idle and drive rolls off of
their plastic hubs.
6. Remove the inside wire guide plate.
7. Replace the drive and idle rolls and inside wire
guide with a set marked for the new wire size.
NOTE: Be sure that the gun liner and contact tip are
also sized to match the selected wire size.

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8. Manually feed the wire from the wire reel, over the
drive roll groove and through the wire guide and
then into the brass bushing of the gun and cable
assembly.
9. Replace the outside wire guide retaining plate by
tightening the two large knurled screws.
Reposition the adjustable pressure arm to its original position to apply pressure. Adjust pressure as
necessary.

WIRE REEL LOADING READI-REELS, SPOOLS, OR COILS
To Mount a 30 lb (14 kg) Readi-Reel
Package (Using the Molded Plastic K363-P
Readi-Reel Adapter:)

RETAINING
COLLAR

GROOVES

READI-REEL
INSIDE
CAGE
WIRES

4. Twist the drive roll retaining mechanism to the
unlocked position.

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ADAPTER
RETAINING
SPRING

3. Remove the outside wire guide retaining plate by
loosening the two large knurled screws.

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B-5

RELEASE
BAR

7. Set one of the Readi-Reel inside cage wires on
the slot in the retaining spring tab.
FIGURE B.2 — READI-REEL INSTALLATION.
8. Lower the Readi-Reel to depress the retaining
spring and align the other inside cage wires with
the grooves in the molded adapter.
9. Slide cage all the way onto the adapter until the
retaining spring “pops up” fully.

CAUTION
Check to be sure the retaining spring has fully returned
to the locking position and has securely locked the
Readi-Reel cage in place. The retaining spring must
rest on the cage, not on the welding
electrode.
-----------------------------------------------------------------------10. To remove Readi-Reel from adapter, depress
retaining spring tab with thumb while pulling the
Readi-Reel cage from the molded adapter with
both hands. Do not remove adapter from spindle.

To Mount 10 to 44 lb (4.5-20 kg) Spools
(12 in./300 mm Diameter) or 14 lb
(6 kg) Innershield Coils:
(For 13-14 lb (6 kg) innershield coils, a K435 coil
adapter must be used).

1. Open the wire drive compartment door.

2. Depress the release bar on the retaining collar
and remove it from the spindle. See Figure B.2.

2. Depress the release bar on the retaining collar
and remove it from the spindle.

3. Place the optional adapter on the spindle.

3. Place the spool on the spindle making certain the
spindle brake pin enters one of the holes in the
back side of the spool (Note: an arrow mark on the
spindle lines up with the brake holding pin to
assist in lining up a hole). Be certain the wire
comes off the reel in a direction that it can de-reel
from the top of the coil.

4. Re-install the retaining collar. Make sure that the
release bar “pops up” and that the collar retainers
fully engage the retaining ring groove on the
spindle.
5. Rotate the spindle and adapter so the retaining
spring is at the 12 o'clock position.
6. Position the Readi-Reel so that it will rotate in a
direction when feeding so as to be de-reeled from
top of the coil.

4. Re-install the retaining collar. Make sure that the
release bar “pops up” and that the collar retainers
fully engage the retaining ring groove on the
spindle.

POWER MIG 255

OPERATION

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B-6

TO START THE WELDER
Turn the Power Switch switch to ON. This lights the red
LED display lights. With the desired voltage and wire
speed selected, operate the gun trigger for welder output and to energize the wire feed motor.

FEEDING WIRE ELECTRODE
WARNING

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When triggering, the electrode and drive mechanism are electrically “hot” relative to work and
ground and remain “hot” several seconds after the
gun trigger is released.
-----------------------------------------------------------------------NOTE: Check that drive rolls, guide plates, and gun
parts are proper for the wire size and type being used.
Refer to Table C.1 in Accessories section.
1. Turn the Readi-Reel or spool until the free end of
the electrode is accessible.
2. While securely holding the electrode, cut off the
bent end and straighten the first six inches. (If the
electrode is not properly straightened, it may not
feed properly through the wire drive system.)
3. Release the pressure on the idle roll by swinging
the adjustable pressure arm down toward the
back of the machine. Lift the cast idle roll assembly and allow it to sit in an upright position. Leave
the outer wire guide plate installed. Manually feed
the wire through the incoming guide bushing and
through the guide plates (over the drive roll
groove). Push a sufficient wire length to assure
that the wire has fed into the gun and cable
assembly without restriction. Reposition the
adjustable pressure arm to its original position to
apply pressure to the wire.
4. Press gun trigger to feed the electrode wire
through the gun.

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IDLE ROLL PRESSURE SETTING
The idle roll pressure adjustment knob is set at the factory at the #2 hash mark. This is an approximate setting. The optimum idle roll pressure varies with type of
wire, wire diameter, surface conditions, lubrication, and
hardness. As a general rule, hard wires may require
greater pressure, and soft, or aluminum wire, may
require less pressure than the factory setting. The optimum idle roll setting can be determined as follows:
1. Press end of gun against a solid object that is
electrically isolated from the welder output and
press the gun trigger for several seconds.

B-6

2. If the wire “birdnests”, jams, or breaks at the drive
roll, the idle roll pressure is too great. Back the
adjustment knob out 1/2 turn, run new wire
through gun, and repeat above steps.
3. If the only result was drive roll slippage, loosen the
adjustment knob on the conductor plate and pull
the gun cable forward about 6 in. (15 cm). There
should be a slight waviness in the exposed wire. If
there is not waviness, the pressure is too low.
Tighten the adjustment knob 1/4 turn, reinstall the
gun cable and repeat the above steps.

SETTING RUN-IN SPEED ON STANDARD POWER MIG FEEDER
FAST OR SLOW RUN-IN MODE SELECTION
(When Timer Option is not installed)
The POWER MIG 255 is factory set for fast run-in
mode where the wire feed will accelerate directly to the
preset wire feed speed when the gun trigger is closed.
Slow run-in mode may also be selected, where it will
initially feed wire at 50 IPM until output current is
sensed or for 1.0 second, whichever occurs first. It will
then accelerate to the preset wire feed speed.
NOTE: See operating instructions for Timer Option Kit
if it is installed, as it provides its own run-in operation.

INSTRUCTIONS TO ENTER SLOW RUN-IN
1. Turn power OFF on front panel of POWER MIG
255.
2. Turn the wire feed speed dial fully counterclockwise to minimum.
3. With the gun trigger closed, turn the power ON at
the front panel of the POWER MIG 255.
4. The display will read “SLO run”.

INSTRUCTIONS TO ENTER FAST RUN-IN
1. Turn power OFF on front panel of POWER MIG
255.
2. Turn the wire feed speed dial fully clockwise to
maximum.
3. With the gun trigger closed, turn the power ON at
the front panel of the POWER MIG 255.
4. The display will read “FAS run”.

POWER MIG 255

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B-7

OPERATION

NOTE: Arc starting characteristics may be effected
when using the fast run-in mode since optimum starting processes are being overridden.

5. If welding gas is to be used, turn on the gas supply and set the required flow rate (typically 25-35
CFH; 12-16 liters/min).

On the initial trigger closure at power up, no output
power or wire feed will be available until the trigger is
opened and reclosed, regardless of wire feed speed
dial setting.

6. When using innershield electrode, the gas nozzle
may be removed from the insulation on the end of
the gun and replaced with the gasless nozzle.
This will give improved visibility and eliminate the
possibility of the gas nozzle overheating.

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It is not necessary to repeat either of the above procedures each time the unit is powered up. The unit will
remember the run-in mode from the previous power
down and return you to that same state upon your next
power up. Therefore, you need only perform one of the
above procedures when you want to change the run-in
mode.

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B-7

7. Connect work cable to metal to be welded. Work
clamp must make good electrical contact to the
work. The work must also be grounded as stated
in Arc Welding Safety Precautions.

WARNING
When using an open arc process, it is necessary
to use correct eye, head, and body protection.
------------------------------------------------------------------------

MAKING A WELD
1. Check that the electrode polarity is correct for the
process being used, then turn the power switch
ON.
2. Set desired arc voltage and wire speed for the
particular electrode wire, material type and thickness, and gas (for GMAW) being used. Use the
Application Chart on the door inside the wire compartment as a quick reference for some common
welding procedures.
3. If Timer Kit is installed, select the desired mode as
described in Operating Instructions for Timer
Kit in the Accessories section. Refer to the
Accessories section for additional welding information pertaining to Spot mode.
4. Press the trigger to feed the wire electrode
through the gun and cable and then cut the electrode within approximately 3/8 in. (10 mm) of the
end of the contact tip [3/4 in. (20 mm)
Outershield®].
NOTE: If set for slow run-in when the trigger is pulled,
the wire feeder feeds wire at low speed regardless of
the set wire feed speed until the welding arc starts or 1
second has elapsed. This feature enhances starting
and makes it easier to set the stickout. The 1 second
limit permits high speed loading of the gun and cable.
To change run-in mode, see Setting Run-In Speed in
this section, if the Timer Kit is not installed, or Timer Kit
Operation section if installed.

8. Position electrode over joint. End of electrode
may be lightly touching the work.
9. Lower welding helmet, close gun trigger, and
begin welding. Hold the gun so the contact tip to
work distance is about 3/8 in. (10 mm) [3/4 in.
(20 mm) for Outershield].
10. To stop welding, release the gun trigger and then
pull gun away from the work after arc goes out.
11. When no more welding is to be done, close valve
on gas cylinder (if used), momentarily operate gun
trigger to release gas pressure, and turn off
POWER MIG 255.

AVOIDING WIRE FEEDING
PROBLEMS
Wire feeding problems can be avoided by observing
the following gun handling procedures:
1. Do not kink or pull cable around sharp corners.
2. Keep the gun cable as straight as possible when
welding or loading electrode through cable.
3. Do not allow dolly wheels or trucks to run over
cables.
4. Keep cable clean by following the maintenance
instructions.

POWER MIG 255

OPERATION

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B-8

5. Use only clean, rust-free electrode. The Lincoln
electrodes have proper surface lubrication.

WIRE FEED OVERLOAD
PROTECTION

6. Replace contact tip when the arc starts to become
unstable or the contact tip end is fused or
deformed.

The POWER MIG has solid state overload protection
of the wire drive motor. If the motor becomes
overloaded, the protection circuitry turns off the wire
feed speed and gas solenoid. Check for proper size
tip, liner, and drive rolls, for any obstructions or bends
in the gun cable, and any other factors that would
impede the wire feeding. To resume welding, simply
pull the trigger. There is no circuit breaker to reset as
the protection is done with reliable solid state
electronics.

7. Keep wire reel spindle brake tension to minimum
required to prevent excess reel over-travel which
may cause wire “loop-offs” from coil.
8. Use proper drive rolls and wire drive idle roll pressure for wire size and type being used.

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FAN CONTROL
The fan is designed to come on automatically when a
weld arc is established. The fan will stay on for a minimum of 6 minutes after the weld arc is terminated. The
fan will also stay on when the machine’s welding and
feeding are disabled during thermostatic over temperature protection. (See Welding Thermal Overload
Protection.)

INPUT LINE VOLTAGE
PROTECTION

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High Line Voltage — If the line voltage exceeds 125%
of rated input voltage, the output will be reduced to the
lower level to protect voltage rating of the capacitor
bank.

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B-8

Low Line Voltage — You may not be able to get maximum output from the machine if the line voltage is less
than rated input. The unit will continue to weld, but the
output may be less than what is set.

WELDING THERMAL
OVERLOAD PROTECTION
The POWER MIG 255 has built-in protective thermostats that respond to excessive temperature. They
open the wire feed and welder output circuits if the
machine exceeds the maximum safe operating temperature because of a frequent overload, or high ambient temperature plus overload. The thermostats automatically reset when the temperature reaches a safe
operating level and welding and feeding are allowed
again, when gun is retriggered.

OVERCURRENT PROTECTION
The machine will automatically reduce the output if the
load on the machine exceeds 300 to 320 amperes.
This protects the welding power SCR’s from excessive
short circuit currents and from exceeding their temperature rating before the thermostats can react.

Welding Procedure Information

100

110

120

Note: See inside cover of machine for additional, commonly used welding procedure information.

POWER MIG 255

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Section C-1

TABLE OF CONTENTS
- ACCESSORIES SECTION -

Section C-1

Accessories ............................................................................................................Section C

Drive Roll Kits ...............................................................................................................C-2
3/64 in. (1.2 mm) Aluminum Feeding Kit (K1703-1) .....................................................C-2
K363P Readi-Reel Adapter ..........................................................................................C-2
Dual Cylinder Mounting Kit (K1702-1)..........................................................................C-2
Alternative Magnum GMAW Gun and Cable Assemblies ............................................C-2

Timer Kit Installation (Optional K1701-1) .....................................................................C-2
Operating Instructions for Timer Kit.......................................................................C-3
Spool Gun Adapter Kit (K1700-1) (Included in the K1692-1).......................................C-4
Making a Weld with the Spool Gun, Spool Gun (K1692-1) Installed.....................C-4

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Magnum Gun Connection Kit (Optional K466-6) .........................................................C-2

POWER MIG 255

ACCESSORIES

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C-2

DRIVE ROLL KITS
Refer to Table C.1 for various drive roll kits that are
available for the POWER MIG. All items in Bold are
supplied standard with the POWER MIG.
TABLE C.1 — AVAILABLE DRIVE ROLL KITS.
Wire
Solid
Steel

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Cored
Aluminum

Size

Drive Roll Kit

0.023-0.030 in. (0.6-0.8 mm) KP1696-030S
0.035 in. (0.9 mm)
KP1696-035S
0.045 in. (1.2 mm)
KP1696-045S
0.035 in. (0.9 mm)
0.045 in. (1.2 mm)

KP1697-035C
KP1697-045C

3/64 in. (1.2 mm)

KP1695-3/64A

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ALTERNATIVE MAGNUM GMAW
GUN AND CABLE ASSEMBLIES
The following Magnum 250L gun and cable assemblies
are separately available for use with the POWER MIG
255. Each is rated 200 amps 60% duty cycle (or 250
amps 40% duty) and is equipped with the integrated
connector, twist-lock trigger connector, fixed nozzle
and insulator, and includes a liner, diffuser, and contact
tips for the wire sizes specified:

Length

Part No.

10 ft (3.0 m)
*12 ft (3.6 m)
15 ft (4.5 m)

K533-1
K533-7
K533-3

English Wire
Size

Metric Wire
Size

0.035 – 0.045 in. 0.9 – 1.2 mm

*Fixed Nozzle

MAGNUM GUN CONNECTION KIT
(Optional K466-6)

3/64 in. (1.2 mm) ALUMINUM
FEEDING KIT (K1703-1)
This kit helps push feeding aluminum through standard
machine feeder and gun. It provides gun and wire drive
conversion parts to weld with 3/64 in.
(1.2 mm) aluminum wire. 5356 alloy aluminum wire is
recommended for best push feeding performance.
Kit includes drive rolls and wire guide plate for the wire
drive, liner and two contact tips for the gun, along with
installation instructions.

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C-2

Using the optional K466-6 Magnum Connection Kit for
the POWER MIG permits use of standard Magnum
200, 300 or 400 gun and cable assemblies.

TIMER KIT INSTALLATION
(Optional K1701-1)
The timer kit adds selectable 4-step trigger interlock,
spot and Run-In functions and manual adjustment of
burnback time. Install as follows, or per the instructions
included with the kit:

K363P READI-REEL ADAPTER
The K363P Readi-Reel adapter mounts to the
2 in. spindle. It is needed to mount the 22-30 lb ReadiReels.

WARNING
Remove all input power to the POWER MIG 255
before proceeding.
-----------------------------------------------------------------------1. Verify that the following items have been included
in the kit:

DUAL CYLINDER
MOUNTING KIT (K1702-1)
Permits stable side-by-side mounting of two full size (9
in. dia. x 5 ft. high) gas cylinders with “no lift” loading.
Simple installation and easy instructions provided.
Includes upper and lower cylinder supports, wheel
axles and mounting hardware.

a. Timer board with harness and panel
assembly.
b. Two screws.
2. Turn the power switch off and disconnect power
from the machine to prepare for kit installation.

POWER MIG 255

ACCESSORIES

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C-3

3. Using a screwdriver, remove the two screws
securing the lower cover panel to the front of the
machine. Remove the lower cover panel.
4. Attach the rectangular 10-pin plug connector on
the timer kit wiring harness to the mating receptacle connector located directly behind the removed
cover panel. Be sure that the latch on the connector is aligned with the one on the board and insert
it until the latch engages.

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5. Align the timer panel for installation and carefully
insert the printed circuit board and wiring harness
through the opening. Make sure the wiring harness is not pinched between panels or between
printed circuit board and front panel cover.
6. Secure the timer assembly with either the two
supplied screws or with the original screws. The
installation is now complete. Refer to the following
section for operating instructions.

OPERATING INSTRUCTIONS
FOR TIMER KIT
If the optional Timer Kit (K1701-1) is installed, select
the desired mode with the selector switch:

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1. Normal Welding mode provides weld power only
while the trigger switch is depressed. This is the
same operation as when the Timer Kit is not
installed.
2. 4-Step Trigger interlock mode eliminates the
need to hold the gun trigger while welding. It operates in 4 steps:
a. Close trigger and establish welding arc.
b. Release trigger and continue welding.

3. Spot Weld Mode is used for tack welding parts
into position or for spot plug welds to hold thin
sheet metal together prior to manual stitch or continuous welding. To use this feature, adjust the
On-Time (0-5 seconds) as appropriate to obtain
the desired results. Closing the trigger initiates a
single timed spot weld cycle. Plug welds are made
by using a punch to make a 3/16 in. (5 mm) diameter hole in the top sheet and arc welding through
the hole into the back sheet.
To make spot plug welds, punch 3/16 in. (5 mm)
holes in the top sheet. Set the Spot Time control
to approximately 1.2 seconds and set the procedure for the metal thickness to be welded. Install
spot weld nozzle (if available) on gun and press it
against the top sheet so the top and bottom
sheets are tight together. Close trigger and hold it
closed until the arc goes out. If a spot weld nozzle
is not used, smoother welds will result by moving
the welding wire in a small circle during the weld.
4. Burnback Time control provides manual adjustment of the burnback time (0-250 milliseconds) for
any selected welding mode. This control should
be set as low as possible without the wire “sticking” in the puddle after each weld. Too long of a
burnback time may form a “ball” on the end of the
wire, or may “flash back” to the gun tip.
5. Run-In Mode is used to adjust the starting wire
feed speed. Starting conditions for certain welding
applications can be improved with adjustment to
the Run-In speed. The control allows for initial
starting speeds from 50 to 150 IPM. After the arc
is started, the set point on the wire feed speed
control will dominate. Note that the Run-in is not
functional with the spool gun. Also note that if
Run-in is set fully counterclockwise to OFF, Runin speed will equal the preset WFS on the
machine.

c. Reclose trigger near end of weld.
d. Release trigger again to stop welding.

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If the arc is broken while using this feature, the
machine will reset to the “trigger off” condition
automatically.
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C-3

POWER MIG 255

ACCESSORIES

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C-4

SPOOL GUN ADAPTER KIT
WARNING
Remove all input power to the POWER MIG 255
before proceeding.
-----------------------------------------------------------------------The Spool Gun Adapter Kit provides direct connection
and use of the Spool Gun (with remote speed control)
with the POWER MIG 255 wire feed welder.

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It also provides gun trigger switch transfer between the
machine’s use with its feeder gun or the spool gun for
same polarity welding with different wire and gas
processes.
The kit includes a spool gun adapter module assembly
with a single connecting plug, a rear gas inlet setting
with hose and mounting hardware with installation and
operation instructions.
K2297-1

Prince® XL Spool Gun with Adaptor Included

K2310-1* Power MIG 255 Spool Gun Adaptor Kit
(connects Magnum® SG Spool Gun OR
Prince® XL Spool Gun

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K487-25 Magnum® SG Spool Gun (requires K23101 Adaptor Kit

*This kit can only be configured to run a Magnum® SG
Spool Gun OR a Prince® XL Spool Gun at a time; kit is
shipped configured for the Magnum® SG Spool Gun.

MAKING A WELD WITH THE SPOOL GUN,
SPOOL GUN INSTALLED
The POWER MIG control circuitry is designed to
sense either the spool gun (built in) wire feeder trigger
circuitry. After the spool gun adapter kit has been
installed, the spool gun can easily be plugged in and
will be ready to use.

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1.Pulling the trigger for the built-in feeder gun:
a. Disables spool gun operation.
b. Closing feeder gun trigger starts feeder gun
welding and makes both electrodes electrically “HOT”.
2. Pulling SPOOL GUN Trigger:
a. Disables built-in feeder gun operation.
b. Closing spool gun trigger starts spool gun
welding and makes both electrodes electrically “HOT”.
3. Operation with POWER MIG 255:
a. Turn the POWER MIG-255 input power
ON.
b. Adjust the voltage control to increase or
decrease your welding voltage.
c. Adjust the wire speed control on the spool
gun to increase or decrease the spool gun
wire feed speed.
Wire Dia.
In. (mm)

WFS Setting
Spool Gun

Arc Voltage
Setting

0.030 in. (0.8 mm)
0.035 in. (0.9 mm)
3/64 in. (1.2 mm)

270
250
240

15V
16V
20V

4. The following procedure settings for Aluminum
4043 can be used as initial settings for making
test welds to determine final settings:
5. To return to normal POWER MIG 255 welding
release the spool gun trigger and reset feeder
gun voltage procedure setting if necessary.

CAUTION

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C-4

Closing either gun trigger will cause the electrode of
both guns to be electrically “HOT”. Be sure unused gun
is positioned so electrode or tip will not contact metal
case or other metal common to work.

6. Operation with Timer Option Kit (K1701-1)
installed in Power MIG 255:
All Timer Option Kit functions, except Run-in,
are functional with the spool gun. (See operating instructions for Timer Option Kit.

POWER MIG 255

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Section D-1

TABLE OF CONTENTS
- MAINTENANCE SECTION -

Section D-1

Maintenance ...........................................................................................................Section D

Safety Precautions ........................................................................................................D-2
Routine and Periodic Maintenance ...............................................................................D-2
Drive Rolls and Guide Tubes .........................................................................................D-2
Cable Cleaning ..............................................................................................................D-2
Gun Tubes and Nozzles ................................................................................................D-2

Liner Removal and Replacement ..................................................................................D-4
Liner Removal, Installation, and Trimming Instructions for Magnum 250L ..................D-4
Gun Handle Disassembly ..............................................................................................D-5
Accessories and Expendable Replacement Parts for Magnum 250L Gun and Cable Assemblies ............D-6

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Contact Tip and Gas Nozzle Installation.......................................................................D-4

POWER MIG 255

MAINTENANCE

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D-2

SAFETY PRECAUTIONS

D-2

DRIVE ROLLS AND GUIDE TUBES

WARNING
• Have a qualified electrician do the maintenance
and troubleshooting work.
• Disconnect the input power off using the disconnect switch at the main input supply before
working inside machine.

After every coil of wire, inspect the wire drive mechanism. Clean it as necessary by blowing with low pressure compressed air. Do not use solvents for cleaning
the idle roll because it may wash the lubricant out of
the bearing. All drive rolls are stamped with the wire
sizes they will feed. If a wire size other than that
stamped on the roll is used, the drive roll must be
changed.

• Unplug the power cable if it is connected to a
receptacle.
------------------------------------------------------------------------

CABLE CLEANING

Read the Safety Precautions in the front of this manual before working on this machine.

Clean the cable liner after using approximately 300
pounds (136 kg) of electrode.
1. Remove the cable from the wire feeder and lay it
out straight on the floor.

ROUTINE AND PERIODIC
MAINTENANCE

2. Remove the contact tip from the gun.

1. Disconnect input AC power supply lines to the
machine before performing periodic maintenance,
tightening, cleaning, or replacing parts.

3. With an air hose at the gas diffuser end, use low
pressure to gently blow out the cable liner.

CAUTION

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Perform the following daily:
1. Check that no combustible materials are in the
welding or cutting area or around the machine.

Excessive pressure at the start may cause the dirt to
form a plug.
------------------------------------------------------------------------

2. Remove any debris, dust, dirt, or materials that
could block the air flow to the machine.

4. Flex the cable over its entire length and again blow
out the cable.

3. Inspect the electrode cables for any slits, punctures in the cable jacket, or any condition that
would affect the proper operation of the machine.

5. Repeat this procedure until no more dirt comes
out.

GUN TUBES AND NOZZLES

Perform Periodically:

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Clean the inside of the machine with low pressure air
stream. Clean the following parts. Refer to Figure D.1.
Main transformer and output choke.
Power enhancement choke.
Wire drive assembly.
Capacitor bank.
SCR rectifier bridge and heat sink fins.
Fan motor assembly.
Control printed circuit board.
Snubber printed circuit board.

1. Replace worn contact tips as required.
2. Remove spatter from the inside of the gas nozzle
and tip every 10 minutes of arc time or as required.

NOTE: The fan motor has sealed bearings which
require no maintenance.

POWER MIG 255

MAINTENANCE

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D-3

FIGURE D.1 — COMPONENT LOCATIONS.

FAN
MOTOR
ASSEMBLY

CONTROL PC
BOARD

SNUBBER
PC BOARD
WIRE DRIVE
ASSEMBLY
SCR
RECTIFIER
BRIDGE

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OUTPUT
CHOKE

CAPACITOR
BANK

MAIN
TRANSFORMER
POWER
ENHANCEMENT
CHOKE

POWER MIG 255

MAINTENANCE

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D-4

CONTACT TIP AND GAS
NOZZLE INSTALLATION
1. Choose the correct size contact tip for the electrode being used (wire size is stenciled on the side
of the contact tip) and screw it snugly into the gas
diffuser.
a. Be sure the nozzle insulator is fully screwed
onto the gun tube and does not block the gas
holes in the diffuser.

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2. Slip or screw the appropriate gas nozzle onto the
nozzle insulator.
NOTE: Either a standard 0.50 in. (12.7 mm) or optional 0.62 in. (15.9 mm) I.D. slip-on gas nozzle may be
used and should be selected based on the welding
application.

LINER REMOVAL, INSTALLATION,
AND TRIMMING INSTRUCTIONS
FOR MAGNUM 250L
NOTE: The variation in cable lengths prevents the
interchangeability of liners between guns. Once a liner
has been cut for a particular gun, it should not be
installed in another gun unless it can meet the liner cut
off length requirement. Liners are shipped with the
jacket of the liner extended the proper amount.
1. Remove the gas nozzle and nozzle insulator. See
Figure D.2.
2. Locate the set screw in the gas diffuser which is
used to hold the old liner in place.
3. Loosen the set screw with a 5/64 in. (2.0 mm) Allen
wrench.
4. Remove the gas diffuser from the gun tube.

3. Adjust the gas nozzle as appropriate for the
GMAW process to be used.
a. Typically, the contact tip end should be flush
to extended 0.12 in. (3.2 mm) for the shortcircuiting transfer process and recessed 0.12
in. (3.2 mm) for spray transfer.

5. Lay the gun and cable out straight on a flat surface.
6. Loosen the set screw located in the brass cable
connector at the feeder end of the cable and pull
the liner out of the cable.
7. Insert a new untrimmed liner into the connector
end of the cable.
a. Check the liner bushing stencil to make sure
it is the appropriate one for the wire size being
used.

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LINER REMOVAL AND
REPLACEMENT

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D-4

NOTE: When you change wire size, a replacement
gas diffuser is required. Use the table below to select
the proper diffuser so the liner is held securely in place.

8. Fully seat the liner bushing into the connector.

Replacement
Liner
Part Number

Size Stenciled on
End of Liner
Bushing

Fixed Nozzle Gas
Diffuser Part No.
(and Stencil)

Adjustable Nozzle
Gas Diffuser Part
No. (and Stencil)

0.025-0.030 in. Steel
(0.6-0.8 mm)

KP1934-2

0.030 in. (0.8 mm)

KP2026-3

KP2026-2

0.035-0.045 in. Steel
(0.9-1.2 mm)

KP1934-1

0.045 in. (1.2 mm)

KP2026-3

KP2026-1B1

3/64 in. Aluminum
(1.2 mm)

KP1955-1

3/64 in. (1.2 mm)

KP2026-3

KP2026-1B1

Diameter of
Electrodes Used

POWER MIG 255

MAINTENANCE

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D-5

9. Tighten the setscrew on the brass cable
connector.

The internal parts of the gun handle may be inspected
or serviced if necessary.

10. Straighten the cable with the gas nozzle and nozzle insulator removed from the gun tube.

The gun handle consists of two halves that are held
together with a collar on each end.

11. Trim the liner to the length shown in Figure D.2.

To open up the handle:

BRASS CABLE
CONNECTOR

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SET
SCREW

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GUN HANDLE DISASSEMBLY

NOTE: Do not install the gas diffuser onto the end of
the gun tube at this time.

FIGURE D.2 — LINER MAINTENANCE.

1. Turn the collars approximately 60 degrees counterclockwise (the same direction as removing a
right hand thread) until the collar reaches a stop.
2. Pull the collar off the gun handle.

1-1/4" (1.25)
(31.8MM)
LINER TRIM
LENGTH

NOTE: If the collars are difficult to turn, position the
gun handle against a corner, place a screwdriver
against the tab on the collar and give the screwdriver a
sharp blow to turn the collar past an internal locking rib.
See Figure D.3.

FIGURE D.3 — GUN HANDLE DISASSEMBLY.

GAS DIFFUSER
NOZZLE INSULATOR

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GAS NOZZLE

12. Remove any burrs from the end of the liner.
13. Screw the gas diffuser onto the end of the gun tube
and tighten.
NOTE: Be sure the gas diffuser is correct for the liner
being used. (See table and diffuser stencil.)
14. Slightly tighten the set screw in the side of the gas
diffuser against the cable liner using 5/64 in.
(2.0 mm) Allen wrench.

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CAUTION

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D-5

This screw should only be gently tightened. Over tightening will split or collapse the liner and cause poor wire
feeding.
------------------------------------------------------------------------

POWER MIG 255

MAINTENANCE

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D-6

ACCESSORIES AND EXPENDABLE REPLACEMENT PARTS FOR
MAGNUM 250L GUN AND CABLE ASSEMBLIES
TABLE D.2
DESCRIPTION

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ENGLISH SIZE

METRIC SIZE

0.025-0.030 in.
0.035-0.045 in.
3/64 in. (Alum. Wire)

0.6 - 0.8 mm
0.9 - 1.2 mm
1.2 mm (Alum. Wire)

KP1934-2
KP1934-1
KP1955-1

Contact Tips
Standard Duty

KP2020-6B1
KP2020-7B1
KP2020-1B1*
KP2020-2B1*

0.025
0.030
0.035
0.045

KP2021-1B1
KP2021-2B1

0.035 in.
0.045 in.

0.9 mm
1.2 mm

KP2021-5B1
KP2021-6B1
KP2022-1B1
KP2022-2B1

0.025
0.030
0.035
0.045

0.6
0.8
0.9
1.2

Tapered

Tab (For Aluminum)
Gas Nozzles
Fixed (Flush)

(Recessed)

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PART NO.

Cable Liner
For 15 ft (4.5 m) or Shorter Cable

Heavy Duty

(Requires: Gas Diffuser Assembly)
Adjustable Slip-On

KP2010-5B1

3/64 in. (Alum. wire)

mm
mm
mm
mm

1.2 mm (Alum. Wire)
9.5 mm
12.1 mm
15.9 mm

KP1930-1
KP1930-2
KP1930-3

3/8 in.
5/8 in.
5/8 in.

9.5 mm
15.9 mm
15.9 mm

KP2026-3*

0.025-0.045 in.

KP1935-2
KP1935-1

1/2 in.
5/8 in.

(Requires: Gas Diffuser Assembly)

KP2026-2
KP2026-1
KP1947-1**
KP2015-1*
KP2041-1

* Included with Power MIG 255.
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in.
in.
in.
in.

0.6
0.8
0.9
1.2

3/8 in.
1/2 in.
5/8 in.

KP2025-1

Gasless Nozzle (for Innershield®)

in.
in.
in.
in.

KP1931-1
KP1931-2*
KP1931-3

(Requires: Nozzle Insulator Assembly)

Gun Tube Assembly
Standard (60 Degrees)
45 Degrees

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D-6

** Requires S19418-1 Gas Diffuser Assembly.

POWER MIG 255

0.25-0.030 in.
0.35-0.045 in.

0.6-1.2 mm
12.7 mm
15.9 mm

0.6-0.8 mm
0.9-1.2 mm

TABLE OF CONTENTS
- THEORY OF OPERATION SECTION -

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Section E-1

Theory of Operation ...............................................................................................Section E

Input Line Voltage and Main Transformer.....................................................................E-2
Output Rectification and Feedback Control.................................................................E-3
Constant Voltage Output ..............................................................................................E-4
Wire Drive Motor and Feedback...................................................................................E-5
Thermal and Overload Protection.................................................................................E-6
Overcurrent Protection ...........................................................................................E-6

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Wire Feed Overload Protection ..............................................................................E-6
SCR Operation..............................................................................................................E-7

FIGURE E.1 – BLOCK LOGIC DIAGRAM
GAS
SOLENOID

FAN
MOTOR

WIRE
DRIVE
MOTOR

WIRE
SPEED
ARC
VOLTAGE

CONTROL
BOARD

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TACH
115 VAC
RECTIFIER
DIODE
BRIDGE
30 VAC
SNUBBER
BOARD

LINE
SWITCH

G
A
T
E

MAIN
TRANSFORMER
SCR
RECTIFIER

FEEDBACK

S
I
G
N
A
L

POWER
ENHANCEMENT
CHOKE

RECONNECT

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GUN TRIGGER

C
A
P
A
C
I
T
O
R
S

F
E
E
D
B
A
C
K

SHUNT

POWER MIG 255

OUTPUT
CHOKE

POSITIVE
TERMINAL

NEGATIVE
TERMINAL

THEORY OF OPERATION

GAS
SOLENOID

FAN
MOTOR

WIRE
DRIVE
MOTOR

WIRE
SPEED
CONTROL
BOARD

ARC
VOLTAGE

TACH
115 VAC
RECTIFIER
DIODE
BRIDGE
30 VAC
SNUBBER
BOARD

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LINE
SWITCH

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E-2

FIGURE E.2 — INPUT LINE VOLTAGE AND MAIN TRANSFORMER.

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E-2

GUN TRIGGER
G
A
T
E

FEEDBACK

S
I
G
N
A
L

POWER
ENHANCEMENT
CHOKE

RECONNECT
MAIN
TRANSFORMER
SCR
RECTIFIER

C
A
P
A
C
I
T
O
R
S

F
E
E
D
B
A
C
K

OUTPUT
CHOKE

POSITIVE
TERMINAL

NEGATIVE
TERMINAL

SHUNT

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INPUT LINE VOLTAGE
AND MAIN TRANSFORMER
The desired single phase input power is connected to
the POWER MIG 255 through a line switch located on
the front panel.
A reconnect panel allows the user to configure the
machine for the desired input voltage. This AC input
voltage is applied to the primary of the main transformer. The main transformer converts the high
voltage, low current input power to a low voltage, high
current output. In addition, the main transformer also
has an isolated center tapped 30 VAC auxiliary winding
that supplies power to the Control Board for the SCR

gate drive circuitry. The weld power windings connect
to the main SCR Rectifier and via the Snubber Board
to the Rectifier Diode Bridge. This AC voltage is rectified and then regulated by the control board. The
resultant +15 VDC and +5 VDC voltages supply power
to the control board circuitry. The 115 VAC winding (X8
and X9) supplies power, through the control board, to
the thermostatically controlled fan motor.
The fan is designed to come on automatically when
weld arc is established. The fan will stay on for a minimum of six minutes after the weld arc is terminated.
The fan will also stay on when the machine’s welding
and feeding are disabled during thermostatic over-temperature protection. (See Thermal and Overload
Protection.)

NOTE: Unshaded areas of Block Logic
Diagram are the subject of discussion

POWER MIG 255

THEORY OF OPERATION

GAS
SOLENOID

FAN
MOTOR

WIRE
DRIVE
MOTOR

WIRE
SPEED
CONTROL
BOARD

ARC
VOLTAGE

TACH
115 VAC
RECTIFIER
DIODE
BRIDGE
30 VAC
SNUBBER
BOARD

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LINE
SWITCH

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E-3

FIGURE E.3 — OUTPUT RECTIFICATION AND FEEDBACK.

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E-3

GUN TRIGGER
G
A
T
E

FEEDBACK

S
I
G
N
A
L

POWER
ENHANCEMENT
CHOKE

RECONNECT
MAIN
TRANSFORMER
SCR
RECTIFIER

C
A
P
A
C
I
T
O
R
S

F
E
E
D
B
A
C
K

OUTPUT
CHOKE

POSITIVE
TERMINAL

NEGATIVE
TERMINAL

SHUNT

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OUTPUT RECTIFICATION AND
FEEDBACK CONTROL
The AC output from the main transformer secondary
weld winding is rectified and controlled through the
SCR rectifier assembly. Output voltage and current are
sensed at the shunt and output terminals and are fed
back to the control board. The control board compares

the commands of the ARC Voltage Control potentiometer with the feedback signals. The appropriate
gate firing pulses are generated by the control board
and applied to the SCR rectifier assembly. The control
board controls the firing of the SCRs, thus controlling
the output of the machine. See SCR Operation. The
control board also powers and commands the gas
solenoid, fan motor, and the wire drive motor.

NOTE: Unshaded areas of Block Logic
Diagram are the subject of discussion

POWER MIG 255

THEORY OF OPERATION

GAS
SOLENOID

FAN
MOTOR

WIRE
DRIVE
MOTOR

WIRE
SPEED
CONTROL
BOARD

ARC
VOLTAGE

TACH
115 VAC
RECTIFIER
DIODE
BRIDGE
30 VAC
SNUBBER
BOARD

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LINE
SWITCH

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E-4

FIGURE E.4 — CONSTANT VOLTAGE OUTPUT.

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E-4

GUN TRIGGER
G
A
T
E

FEEDBACK

S
I
G
N
A
L

POWER
ENHANCEMENT
CHOKE

RECONNECT
MAIN
TRANSFORMER
SCR
RECTIFIER

C
A
P
A
C
I
T
O
R
S

F
E
E
D
B
A
C
K

OUTPUT
CHOKE

POSITIVE
TERMINAL

NEGATIVE
TERMINAL

SHUNT

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CONSTANT VOLTAGE OUTPUT
The controlled DC output from the SCR rectifier
assembly is supplied to the power factor enhancement
choke which limits the rate at which the supply current
rises through the capacitors. The DC output from the

power factor enhancement choke is filtered by the
capacitor bank resulting in a constant voltage DC output. Since the output choke is in series with the positive leg of the rectifier and also in series with the gun
and welding load, a filtered constant voltage output is
applied to the output terminals of the machine.

NOTE: Unshaded areas of Block Logic
Diagram are the subject of discussion

POWER MIG 255

THEORY OF OPERATION

GAS
SOLENOID

FAN
MOTOR

WIRE
DRIVE
MOTOR

WIRE
SPEED
CONTROL
BOARD

ARC
VOLTAGE

TACH
115 VAC
RECTIFIER
DIODE
BRIDGE
30 VAC
SNUBBER
BOARD

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LINE
SWITCH

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E-5

FIGURE E.5 — WIRE DRIVE MOTOR AND FEEDBACK.

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E-5

GUN TRIGGER
G
A
T
E

FEEDBACK

S
I
G
N
A
L

POWER
ENHANCEMENT
CHOKE

RECONNECT
MAIN
TRANSFORMER
SCR
RECTIFIER

C
A
P
A
C
I
T
O
R
S

F
E
E
D
B
A
C
K

OUTPUT
CHOKE

POSITIVE
TERMINAL

NEGATIVE
TERMINAL

SHUNT

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WIRE DRIVE MOTOR
AND FEEDBACK
The wire drive motor is controlled by the control board.
A motor speed feedback signal is generated at the
motor tach and sent to the control board. The control

board compares this feedback signal with the commands set forth by the Wire Speed Control potentiometer and sends the appropriate armature voltage to
the wire drive motor. The drive motor speed is thus
controlled which in turn regulates the electrode wire
feed speed through the gun.

NOTE: Unshaded areas of Block Logic
Diagram are the subject of discussion

POWER MIG 255

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E-6

THEORY OF OPERATION

E-6

OVERCURRENT PROTECTION

THERMAL AND OVERLOAD
PROTECTION
The POWER MIG 255 has built-in protective thermostats that respond to excessive temperatures. One
is located on the output choke. The other thermostat is
located on the SCR heat sink assembly. They open the
wire feed and welder output circuits if the machine
exceeds the maximum safe operating temperature.
This can be caused by a frequent overload, or high
ambient temperature.
The thermostats are self-resetting once the machine
cools sufficiently. If the thermostat shutdown is caused
by excessive output or duty cycle and the fan is operating normally, the power switch may be left on and the
reset should occur within a 15 minute period. If the fan
is not turning or the air intake louvers are obstructed,
then the input power must be removed and the fan
problem or air obstruction be corrected.

The machine will automatically reduce the output if the
load on the machine exceeds 300 to 320 amperes.
This protects the welding power SCR’s from excessive
short circuit currents and from exceeding their temperature rating before the thermostats can react.

WIRE FEED OVERLOAD PROTECTION
The POWER MIG has solid state overload protection
of the wire drive motor. If the motor becomes overloaded, the protection circuitry turns off the wire feed
speed and gas solenoid. Check for proper size tip liner,
and drive rolls, for any obstructions or bends in the gun
cable, and any other factors that would impede the wire
feeding. To resume welding, simply pull the trigger.
There is no circuit breaker to reset, as the protection is
done with reliable solid state electronics.

POWER MIG 255

THEORY OF OPERATION

E-7

FIGURE E.6 — SCR OPERATION.

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E-7

INPUT

CATHODE
OUTPUT

NOTE: AS THE GATE
PULSE IS APPLIED
LATER IN THE CYCLE
THE SCR OUTPUT
IS DECREASED.

ANODE

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GATE

SCR OPERATION
A silicon controlled rectifier (SCR) is a three terminal
device used to control rather large currents to a load.
An SCR acts very much like a switch. See Figure E.6
for a graphical representation of SCR operation. When
a gate signal is applied to the SCR it is turned ON and
there is current flow from anode to cathode. In the ON
state the SCR acts like a closed switch. When the SCR
is turned OFF there is no current flow from anode to
cathode thus the device acts like an open switch. As
the name suggests, the SCR is a rectifier, so it passes
current only during positive half cycles of the AC supply. The positive half cycle is the portion of the sine
wave in which the anode of the SCR is more positive
than the cathode.
When an AC supply voltage is applied to the SCR, the
device spends a certain portion of the AC cycle time in

the off state and the remainder of the time in the on
state. The amount of time spent in the ON state is controlled by the gate.
An SCR is fired by a short burst of current into the gate.
This gate pulse must be more positive than the cathode voltage. Since there is a standard PN junction
between gate and cathode, the voltage between these
terminals must be slightly greater than 0.6V. Once the
SCR has fired it is not necessary to continue the flow
of gate current. As long as current continues to flow
from anode to cathode the SCR will remain on. When
the anode to cathode current drops below a minimum
value, called holding current, the SCR will shut off. This
normally occurs as the AC supply voltage passes
through zero into the negative portion of the sine wave.
If the SCR is turned on early in the positive half cycle,
the conduction time is longer resulting in greater SCR
output. If the gate firing occurs later in the cycle the
conduction time is less resulting in lower SCR output.

POWER MIG 255

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E-8

NOTES

POWER MIG 255

E-8

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Section F-1

TABLE OF CONTENTS
- TROUBLESHOOTING & REPAIR SECTION -

Section F-1

Troubleshooting & Repair Section ........................................................................Section F

How to Use Troubleshooting Guide..............................................................................F-2
PC Board Troubleshooting Procedures and Replacement...........................................F-3
Troubleshooting Guide ..................................................................................................F-4
Test Procedures
Main Transformer Test ..........................................................................................F-11

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Rectifier Diode Bridge Test...................................................................................F-15
Static SCR Rectifier Assembly Test .....................................................................F-19
Active SCR Rectifier Assembly Test.....................................................................F-23
Wire Drive Motor and Tachometer Feedback Test...............................................F-27
Oscilloscope Waveforms
Normal Open Circuit Voltage Waveform ..............................................................F-31
Typical Output Voltage Waveform - Machine Loaded..........................................F-32
Abnormal Output Voltage Waveform - Machine Loaded One Output SCR Not Functioning .............F-33
Abnormal Open Circuit Voltage Output Capacitor Bank Not Functioning...........F-34
Typical SCR Gate Voltage Waveform ...................................................................F-35
Replacement Procedures
Control PC Board Removal and Replacement.....................................................F-37

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Wire Drive Assembly Removal and Replacement ................................................F-41
SCR Output Rectifier Removal and Replacement ...............................................F-45
Capacitor Bank Removal and Replacement ........................................................F-49
Main Transformer and Output Choke Removal and Replacement ......................F-51
Fan Motor and Fan Removal and Replacement ..................................................F-55
Retest After Repair......................................................................................................F-57

POWER MIG 255

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F-2

TROUBLESHOOTING & REPAIR

F-2

HOW TO USE TROUBLESHOOTING GUIDE

CAUTION
Service and repair should be performed by only Lincoln Electric Factory Trained Personnel.
Unauthorized repairs performed on this equipment may result in danger to the technician and machine
operator and will invalidate your factory warranty. For your safety and to avoid Electrical Shock, please
observe all safety notes and precautions detailed throughout this manual.

This Troubleshooting Guide is provided to help
you locate and repair possible machine
malfunctions. Simply follow the three-step
procedure listed below.

Step 1. LOCATE PROBLEM (SYMPTOM). Look
under the column labeled “PROBLEM
(SYMPTOMS)”. This column describes possible
symptoms that the machine may exhibit. Find
the listing that best describes the symptom that
the machine is exhibiting. Symptoms are
grouped into three main categories: Feeding
Problems and Welding Problems.

Step 2. PERFORM EXTERNAL TESTS. The
second column, labeled “POSSIBLE AREAS OF
MISADJUSTMENT(S)”, lists the obvious external
possibilities that may contribute to the machine
symptom. Perform these tests/checks in the
order listed. In general, these tests can be
conducted without removing the case
wrap-around cover.

Step 3. PERFORM COMPONENT TESTS. The
last column, labeled “Recommended Course of
Action” lists the most likely components that may
have failed in your machine. It also specifies the
appropriate test procedure to verify that the
subject component is either good or bad. If there
are a number of possible components, check the
components in the order listed to eliminate one
possibility at a time until you locate the cause of
your problem.

All of the referenced test procedures referred to in
the Troubleshooting Guide are described in detail
at the end of this chapter. Refer to the
Troubleshooting and Repair Table of Contents to
locate each specific Test Procedure. All of the
referred to test points, components, terminal
strips, etc., can be found on the referenced
electrical wiring diagrams and schematics. Refer
to the Electrical Diagrams Section Table of
Contents to locate the appropriate diagram.

CAUTION
If for any reason you do not understand the test procedures or are unable to perform the test/repairs safely, contact the Lincoln Electric Service Department for electrical troubleshooting assistance before you proceed. Call
1-888-935-3877.

POWER MIG 255

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F-3

TROUBLESHOOTING & REPAIR
PC BOARD TROUBLESHOOTING PROCEDURES
WARNING
ELECTRIC SHOCK
can kill.
• Have an electrician install and
service this equipment. Turn the
input power OFF at the fuse box
before working on equipment. Do
not touch electrically hot parts.

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CAUTION

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F-3

Sometimes machine failures appear to be due to PC
board failures. These problems can sometimes be
traced to poor electrical connections. To avoid problems when troubleshooting and replacing PC boards,
please use the following procedure:
1. Determine to the best of your technical ability
that the PC board is the most likely component
causing the failure symptom.
2. Check for loose connections at the PC board
to assure that the PC board is properly
connected.
3. If the problem persists, replace the suspect PC
board using standard practices to avoid static
electrical damage and electrical shock. Read
the warning inside the static resistant bag and
perform the following procedures:
PC board can be damaged by static electricity.
- Remove your body’s static
charge before opening the staticshielding bag. Wear an anti-static
wrist strap. For safety, use a 1
Meg ohm resistive cord connected
to a grounded part of the
ATTENTION
Static-Sensitive equipment frame.
Devices
- If you don’t have a wrist strap,
Handle only at touch an un-painted, grounded,
Static-Safe
part of the equipment frame. Keep
Workstations
touching the frame to prevent

- Remove the PC board from the static-shielding bag
and place it directly into the equipment. Don’t set the
PC board on or near paper, plastic or cloth which
could have a static charge. If the PC board can’t be
installed immediately, put it back in the static-shielding bag.
- If the PC board uses protective shorting jumpers,
don’t remove them until installation is complete.
- If you return a PC board to The Lincoln Electric
Company for credit, it must be in the static-shielding
bag. This will prevent further damage and allow proper failure analysis.
4. Test the machine to determine if the failure
symptom has been corrected by the
replacement PC board.
NOTE: It is desirable to have a spare (known good)
PC board available for PC board troubleshooting.
NOTE: Allow the machine to heat up so that all
electrical components can reach their operating
temperature.
5. Remove the replacement PC board and
substitute it with the original PC board to
recreate the original problem.
a. If the original problem does not reappear by
substituting the original board, then the PC
board was not the problem. Continue to look
for bad connections in the control wiring
harness, junction blocks, and terminal strips.
b. If the original problem is recreated by the
substitution of the original board, then the PC
board was the problem. Reinstall the
replacement PC board and test the machine.
6. Always indicate that this procedure was
followed when warranty reports are to be
submitted.
NOTE: Following this procedure and writing on the
warranty report, “INSTALLED AND SWITCHED PC
BOARDS TO VERIFY PROBLEM,” will help avoid
denial of legitimate PC board warranty claims.

static build-up. Be sure not to
touch any electrically live parts at
the same time.
- Tools which come in contact with the PC board must
be either conductive, anti-static or static-dissipative.

POWER MIG 255

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F-4

TROUBLESHOOTING & REPAIR

TROUBLESHOOTING GUIDE
PROBLEMS
(SYMPTOMS)

F-4

Observe Safety Guidelines
detailed in the beginning of this manual.

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

OUTPUT PROBLEMS
Major Physical or Electrical Damage 1. Contact your local Lincoln 1. Contact The Lincoln Electric
is Evident
Electric Authorized Field Service
Service Dept. 1-888-935-3877
Facility.
1. Check input power switch (S1).
Machine is dead — no open circuit 1. Make certain that the input
It may be faulty.
voltage output and no wire feed
power switch is in the "ON" posiwhen gun trigger is pulled. The
tion.
2. Check for lose or broken wires
machine display may be lit.
at the reconnect panel.
2. Check the input voltage at the
machine. Input voltage must 3. Perform Main Transformer
match the rating plate and the
Test.
reconnect panel.
4. Perform Rectifier Diode Bridge
3. Blown or missing fuses in the
Test.
input line.
5. Check the thermostats and
4. The thermostats may be open
associated leads for loose or
due to machine overheating. If
broken connections. See wiring
machine operates normally after
diagram.
a cooling off period then check
for proper fan operation and 6. The control board may be faulty.
ventilation. Make certain that the
Replace.
machine's duty cycle is not
being exceeded.
5. Check the trigger circuit. Leads
#324 to #325 should have continuity (zero ohms) when the gun
trigger is pulled. If not then the
gun may be faulty — replace.
6. Make sure unit is not connected
to a portable generator.

POWER MIG 255

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F-5

TROUBLESHOOTING & REPAIR

TROUBLESHOOTING GUIDE
PROBLEMS
(SYMPTOMS)

F-5

Observe Safety Guidelines
detailed in the beginning of this manual.

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

OUTPUT PROBLEMS (Continued)
No open circuit voltage output but 1. Check the input voltage at the 1. Check for loose or broken conwire feeds normally when gun trigmachine. Input voltage must
nections at the output terminals,
ger is pulled.
match the rating plate and the
the chokes, the capacitor bank
reconnect panel.
and all heavy current carrying
leads. See Wiring Diagram.
2. The gun may be faulty. Check
or replace.
2. Make sure that the transformer
secondary leads are securely
connected to the SCR rectifier
assembly.
3. Perform the SCR Rectifier
Assembly Tests.
4. Perform
Test.

Main

Transformer

5. The control board may be faulty.
Replace.
Wire feeds but welding output is low 1. Make sure that the proper wire 1. Check for loose or faulty connections of the heavy current
causing wire to “stub”. Welds are
and procedures are being used.
carrying leads.
“cold”. Machine cannot obtain full
rated output of 200 amps at 28 volts. 2. Check gun and work cable for
2. The output capacitor bank may
loose or faulty connections.
be faulty. Check for loose connections at the capacitors. Also
check for leaky capacitors.
Replace if necessary.
WARNING: The liquid electrolyte in these capacitors is
toxic. Avoid contact with any
portion of your body.
3. Perform the SCR Rectifier
Assembly Tests.

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4. Perform the Main Transformer
Test.
5. The control board may be faulty.
Replace.

POWER MIG 255

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F-6

TROUBLESHOOTING & REPAIR

TROUBLESHOOTING GUIDE
PROBLEMS
(SYMPTOMS)

F-6

Observe Safety Guidelines
detailed in the beginning of this manual.

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

OUTPUT PROBLEMS (Continued)
The output voltage and wire feed is 1. Remove the gun. If the problem 1. Check the machine's internal
present continuously or pulsing
is resolved the gun trigger circuit
trigger leads for grounds or
when gun trigger is NOT activated.
is faulty. Repair or replace.
shorts. See Wiring Diagram.

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2. If problem persists when gun 2. The control board may be faulty.
assembly is removed from
Replace.
machine, then the problem is
within the POWER MIG 255.

The output voltage is present contin- Contact your local Lincoln Electric
uously when gun trigger is NOT acti- Authorized Field Service Facility.
vated.

1. Perform the SCR Rectifier
Assembly Tests.
2. The control board may be faulty.
Replace.

POWER MIG 255

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F-7

TROUBLESHOOTING & REPAIR

TROUBLESHOOTING GUIDE
PROBLEMS
(SYMPTOMS)

F-7

Observe Safety Guidelines
detailed in the beginning of this manual.

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

FUNCTION PROBLEMS
No control of arc voltage. Wire feed- 1. The arc voltage control poten- 1. The arc voltage control potening is normal.
tiometer may be dirty. Rotate
tiometer may be faulty. Check or
several times and check if probreplace. See Wiring Diagram.
lem is resolved.
2. Perform the SCR Rectifier
Assembly Tests.

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3. The control board may be faulty.
Replace.

There is no gas flow when gun trig- 1. Check gas source and hoses for 1. Check the gas solenoid by disger is pulled. Wire feeds and weld
leaks or kinks.
connecting it from the control
voltage is present.
board (Plug J8) and applying a
12 VDC external supply to the
gas solenoid. If the solenoid
does NOT activate then it may
be faulty. Replace.

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2. The control broad may be faulty.
Replace.

The machine stops feeding wire 1. Check for adequate wire supply. 1. Check the motor armature current. Normal armature current is
while welding.
2. Check for mechanical restric2.0 to 2.7 amps maximum. If
tions in the wire feeding path.
the motor armature current is
normal the control board may be
The gun may be clogged.
faulty. Replace.
3. Check gun liner and tip are cor2. If the motor armature current is
rect for wire size being used.
high (over 2.7 amps) and there
4. Check spindle for ease of rotaare NO restrictions in the wire
tion.
feeding path then the motor or
gear box may be defective.
5. If Timer Option Kit is installed,
Replace.
make sure spot timer knob is set
to OFF.

POWER MIG 255

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F-8

TROUBLESHOOTING & REPAIR

TROUBLESHOOTING GUIDE
PROBLEMS
(SYMPTOMS)

F-8

Observe Safety Guidelines
detailed in the beginning of this manual.

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

WIRE FEEDING PROBLEMS
No control of wire feed speed. Other 1. The wire feed speed control 1. The Wire Speed Control potenmachine functions are normal
may be dirty. Rotate several
tiometer may be faulty. Check or
times and check if problem is
replace. See Wiring Diagram.
resolved.
2. Perform the Wire Drive Motor
and Tachometer Feedback
Test.

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3. The control board may be faulty.
Replace.

There is no wire feed when gun trig- 1. Check for adequate wire supply. 1. Perform the Wire Drive Motor
ger is pulled. Normal open circuit
and Tachometer Feedback
voltage is present.
2. If the drive rolls are turning then
Test.
check for a mechanical restric2. The Wire Feed Control potention in the wire feed path.
tiometer may be faulty. Check or
replace. See Wiring Diagram.
3. The gun liner may be clogged.
Check or replace.
3. The control board may be faulty.
Replace.
4. If the drive rolls are NOT turning
when the gun trigger is pulled
then contact your local Lincoln
Electric Authorized Field Service
Facility.

POWER MIG 255

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F-9

TROUBLESHOOTING & REPAIR

TROUBLESHOOTING GUIDE
PROBLEMS
(SYMPTOMS)

F-9

Observe Safety Guidelines
detailed in the beginning of this manual.

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

WELDING PROBLEMS
The arc is unstable and or “hunting”. 1. Check for worn or melted con- 1. Check for loose connections at
tact tip.
the output terminals, the
chokes, the capacitor bank and
2. Check for loose or faulty conall heavy current carrying leads.
nections on the work and elecSee Wiring Diagram.
trode cables.
2. Make sure that the transformer
3. Make sure electrode polarity or
secondary leads are securely
welding process being used, is
connected to the SCR rectifier
correct.
assembly.
4. Check for rusty or dirty wire.

3. The output capacitor bank may
be faulty. Check for loose con5. Make sure machine settings and
nections at the capacitors. Also
gas are correct for process
check for leaky capacitors.
being used.
Replace if necessary.
WARNING: The liquid electrolyte in these capacitors is
toxic. Avoid contact with any
portion of your body.
4. Perform the SCR Rectifier
Assembly Tests.

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5. The control board may be faulty.
Replace.
Weld bead is narrow or ropy. May 1. Make sure the weld procedure 1. The output capacitor bank may
have porosity with electrode stuband electrode polarity is correct
be faulty. Check for loose conbing into plate.
for the process being used.
nections at the capacitors. Also
check for leaky capacitors.
2. Make sure shielding gas is corReplace if necessary.
rect and flow is proper.
WARNING: The liquid elec3. Make sure the weld joint is not
trolyte in these capacitors is
“contaminated”.
toxic. Avoid contact with any
portion of your body.

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2. The control board may be faulty.
Replace.

POWER MIG 255

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F-10

TROUBLESHOOTING & REPAIR

TROUBLESHOOTING GUIDE
PROBLEMS
(SYMPTOMS)

F-10

Observe Safety Guidelines
detailed in the beginning of this manual.

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

WELDING PROBLEMS (Continued)
The contact tip seizes in the gas
diffuser.

1. The tip being over heated due to 1. Make sure tip is tight in diffuser.
excessive current and/or high
duty cycle welding.

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2. A light application of high temperature anti-sieze lubricant
(such as Lincoln E2607
Graphite Grease) may be
applied to the contact tip
threads.

The welding arc is variable and
sluggish.

1. Check the welding cable con- 1. Perform the SCR Rectifier
nections for loose or faulty conAssembly Tests.
nections.
2. The control board may be faulty.
2. Make sure the wire feed speed,
Replace.
voltage, and shielding gas are
correct for the process being
used.

The arc striking is poor.

1. Check the welding cable con- 1. The output capacitor bank may
nections for loose or faulty conbe faulty. Check for loose connections.
nections at the capacitors. Also
check for leaky capacitors.
2. Make sure the wire feed speed,
Replace if necessary.
voltage, and shielding gas are
correct for the process being
WARNING: The liquid elecused.
trolyte in these capacitors is
toxic. Avoid contact with any
portion of your body.
2. The control board may be faulty.
Replace.

POWER MIG 255

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F-11

TROUBLESHOOTING & REPAIR
MAIN TRANSFORMER TEST
WARNING
Service and repair should be performed by only Lincoln Electric factory trained
personnel. Unauthorized repairs performed on this equipment may result in danger
to the technician or machine operator and will invalidate your factory warranty. For
your safety and to avoid electrical shock, please observe all safety notes and precautions detailed throughout this manual.

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If for any reason you do not understand the test procedures or are unable to perform the test / repairs safely, contact the Lincoln Electric Service Department for
electrical troubleshooting assistance before you proceed. Call 1-888-935-3877.

TEST DESCRIPTION
This procedure will determine if the correct voltages are being:
a. Applied to the primary windings of the main transformer.
b. Induced on the secondary and auxiliary windings of the main transformer.

MATERIALS NEEDED
Volt/Ohm Meter

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3/8 in. Nutdriver
5/16 in. Nutdriver

POWER MIG 255

F-11

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F-12

TROUBLESHOOTING & REPAIR
MAIN TRANSFORMER TEST (continued)
FIGURE F.1 — G3521 CONTROL PC BOARD AND M19248 SNUBBER PC BOARD
MAIN TRANSFORMER TEST POINTS.

X5
(6J6)
J6

J5
#206
(3J5)
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X6
(5J6)
X7
(4J6)

X9
(8J5)

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F-12

X8
(16J5)

#209S
(6J9)

J3
J8

J9
#208S
(2J9)

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TEST PROCEDURE

WARNING

4. Locate plug J5 and plug J6 on the
G3521 control PC board, and J9 on the
M19248 snubber PC board. See Figure
F.1.

The ON/OFF POWER SWITCH will be
“hot” during these tests.
----------------------------------------------------------

NOTE: The location of plugs may vary
depending on the machine code.

NOTE: Secondary voltages will vary proportionately with the primary input voltage.

5. Locate the following leads on plug J6
on the G3521 control PC board:

1. Disconnect the main input power supply to the machine.

LEAD

PLUG
LOCATION

2. Remove the case top and side panels
with a 3/8 in. nutdriver.

X5
X6
X7

6J6
5J6
4J6

3. Remove the tool tray with a 5/16 in. nutdriver.

POWER MIG 255

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F-13

TROUBLESHOOTING & REPAIR
MAIN TRANSFORMER TEST (continued)
6. Connect main input power to the
machine.
7. Turn the POWER MIG 255 ON/OFF
POWER SWITCH to ON.
8. Carefully make the following voltage
tests at plug J6.

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a. Turn the machine OFF between
each test.
b. Carefully insert the meter probes
into the back of each Molex plug
pin cavity to perform the test.
FROM
LEAD

TO
LEAD

EXPECTED
VOLTAGE

X5
(6J6)

X6
(5J6)

15VAC

X5
(6J6)

X7
(4J6)

30VAC

X6
(5J6)

X7
(4J6)

15VAC

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11. Turn the machine ON.
12. Make the following voltage tests at plug
J5.
a. Turn the machine OFF between
each test.
b. Carefully insert the meter probes
into the back of each Molex plug
pin cavity to perform the test.
FROM
LEAD

TO
LEAD

EXPECTED
VOLTAGE

X8
(16J5)

X9
(8J5)

115VAC

c. If the voltage tested is incorrect,
check for loose or broken leads
between the test points and the
main transformer.
d. If the voltage is not corrected, go to
step 16.
13. Turn OFF the machine power.

9. Turn OFF the machine.

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F-13

10. Locate the following leads on plug J5
on the G3521 control PC board. See
Figure F.1.

LEAD

PLUG
LOCATION

X8
X9

16J5
8J5

POWER MIG 255

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F-14

TROUBLESHOOTING AND REPAIR
MAIN TRANSFORMER TEST (continued)
14. Locate the following leads on plug J9
on the M19248 snubber PC board and
on plug J5 on the G3521 control PC
board. See Figure F.1.
G3521:
LEAD

PLUG
LOCATION

206

3J5

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M19248:
LEAD

PLUG
LOCATION

208S
209S

2J9
6J9

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d. If ALL the voltages tested are incorrect or missing, go to step 16.
17. Test for correct nameplate input
voltage between the H1 lead at the
ON/OFF POWER SWITCH to H2 or
H3 (H5 if connected for 575 VAC) at
the reconnect panel. Voltage tested will
vary depending on input voltage
connection. See wiring diagram for test
point locations.
a. If the voltage test is incorrect,

16. Make the following voltage tests at plug
J9 on the M19248 snubber PC board
and at plug J5 on the G3521 control PC
board.

b. Carefully insert the meter probes
into the back of each Molex plug
pin cavity to perform the test.
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c. If any of the voltages tested are
incorrect, check for loose or broken
leads between the test points and
the main transformer.

15. Turn the machine ON.

a. Turn the machine OFF between
each test.

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F-14

FROM
LEAD

TO
LEAD

EXPECTED
VOLTAGE

208S
(2J9 on
M19248)

209S
(6J9 on
M19248)

56VAC

208S
(2J9 on
M19248)

206
(3J5 on
G3521)

28VAC

209S
(6J9 on
M19248)

206
(3J5 on
G3521)

28VAC

POWER MIG 255

-check for loose or broken leads
between the reconnect panel and
the ON/OFF POWER SWITCH.
-test the ON/OFF POWER
SWITCH for proper operation.
b. If the correct nameplate voltage is
being applied to the main transformer and one or more of the secondary voltages are missing or are
incorrect, the main transformer may
be faulty. Replace.

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F-15

TROUBLESHOOTING & REPAIR
RECTIFIER DIODE BRIDGE TEST

WARNING
Service and repair should only be performed by Lincoln Electric factory trained
personnel. Unauthorized repairs performed on this equipment may result in danger to the technician or machine operator and will invalidate your factory warranty. For your safety and to avoid electrical shock, please observe all safety
notes and precautions detailed throughout this manual.
If for any reason you do not understand the test procedures or are unable to perform the test/repairs safely, contact the Lincoln Electric service department for
technical troubleshooting assistance before you proceed. Call 1-888-935-3877.
-------------------------------------------------------------------------------------------------------------------

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TEST DESCRIPTION
This test will determine if the correct voltages are being:
a. Applied to the diode bridge.
b. Supplied from diode bridge to the control PC board.

MATERIALS NEEDED

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3/8 in. Nutdriver
Volt-ohmmeter
POWER MIG 255 wiring diagrams (See Electrical Diagrams Section of this Manual)

POWER MIG 255

F-15

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F-16

TROUBLESHOOTING & REPAIR
RECTIFIER DIODE BRIDGE TESTING (continued)
FIGURE F.2 — G3521 RECTIFIER DIODE BRIDGE LOCATION.

RECTIFIER
DIODE BRIDGE
(D2)

TEST PROCEDURE
LEAD
1. Disconnect the main AC input power to
the machine.

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2. Remove the case top and side panels
with a 3/8 in. nutdriver.

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F-16

3. Perform the Main Transformer Test to
ensure the proper voltages are supplied
to the M19248 snubber PC board.
4. Locate the following leads:

208R
209R
354
206
Leads #208R, #209R, and #354 are
connected to the rectifier diode bridge
(D2). See Figure F.2. Lead #206 is
connected at the output shunt. See the
wiring diagram.
5. Connect main input power to the
machine.

POWER MIG 255

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F-17

TROUBLESHOOTING & REPAIR
RECTIFIER DIODE BRIDGE TESTING (continued)
6. Turn the POWER MIG 255 ON/OFF
POWER SWITCH to ON.
7. Carefully make the following voltage
tests:
a. Turn the machine OFF between
each test.
b. Carefully connect the meter plugs
to the exposed lead connections.

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c. Turn the machine ON to conduct
the voltage test.

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F-17

FROM
LEAD

TO
LEAD

EXPECTED
VOLTAGE

208R

206

28 VAC

209R

206

28 VAC

8. If any of the AC voltages tested are
incorrect or missing, check the M19248
snubber PC board and associated
leads and connections. See the wiring
diagram.

POWER MIG 255

9. Make the following voltage test:
a. Turn the machine OFF between
each test.
b. Carefully connect the meter probes
to the exposed lead connections.
c. Turn the machine ON to conduct
the voltage test.
FROM
LEAD

TO
LEAD

EXPECTED
VOLTAGE

354

206

36 VDC

10. If the DC voltage tested is incorrect or
missing, and the AC voltages are correct, the rectifier diode bridge may be
faulty.

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F-18

NOTES

POWER MIG 255

F-18

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F-19

TROUBLESHOOTING & REPAIR
STATIC SCR RECTIFIER ASSEMBLY TEST

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TEST DESCRIPTION
This test is used to quickly determine if an SCR or diode is shorted or “leaky.” See the
Machine Waveform Section in this manual for normal and abnormal output waveforms.

MATERIALS NEEDED
Analog Volt-ohmmeter
POWER MIG 255 wiring diagrams (See Electrical Diagrams Section of this Manual)
3/8 in. Nutdriver
5/16 in. Nutdriver
1/2 in. Open end or socket wrench

POWER MIG 255

F-19

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F-20

TROUBLESHOOTING & REPAIR

F-20

STATIC SCR RECTIFIER ASSEMBLY TEST (continued)
FIGURE F.3 — REMOVE PLUGS J6 AND J9 TO PERFORM STATIC RECTIFIER ASSEMBLY TEST.

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J3
J8

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TEST PROCEDURE
1. Disconnect main AC input power to the
machine.
2. Remove the case top and side panels
with a 3/8 in. nutdriver.

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3. Remove the tool tray with a 5/16 in. nutdriver.

POWER MIG 255

4. Verify that the capacitors have
completely discharged with a voltohmmeter.
5. Disconnect plugs J6 from the G3521
control board and J9 from the M19248
snubber PC board. This electrically
isolates the SCR bridge assembly.
See Figure F.3.

TROUBLESHOOTING & REPAIR

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F-21

STATIC SCR RECTIFIER ASSEMBLY TEST (continued)
FIGURE F.4 — LOCATION OF
LEADS X2 AND X3.

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FIGURE F.5 — SCR 1 TEST POINTS.

NEGATIVE
CAPACITOR
BANK BUSS
BAR

LEADS X2 AND X3
CONNECTION

9. Test for high or infinite resistance from
the cathode to the anode of SCR 1 by
reversing the meter leads. See Figure
F.5.
6. Disconnect leads X2 and X3 (braided
copper strap) from the negative capacitor bank buss bar using a 1/2 in. open
end wrench. See Figure F.4.

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F-21

7. Separate leads X2 and X3 from the
negative capacitor bank buss bar. Be
sure there is no electrical contact.

a. If a high or infinite resistance is indicated for both tests 6 and 7, the
SCR 1 is not “shorted”.
b. If a low resistance is indicated in
either tests 6 or 7, the SCR is faulty.
Replace the SCR assembly.
10. Repeat steps 6 and 7 to test SCR 2.

NOTE: DO NOT DISASSEMBLE THE SCR
RECTIFIER HEAT SINK ASSEMBLY.
8. Test for high or infinite resistance from
the anode to the cathode of SCR 1
using an analog ohmmeter. See Figure
F.5.

POWER MIG 255

11. Reconnect leads X2 and X3 (braided
copper strap).
12. Reconnect plugs J9 and J6.
13. If this test did not identify the problem,
or to further test the SCR, go to the
Active SCR Rectifier Assembly Test.

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F-22

NOTES

POWER MIG 255

F-22

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F-23

TROUBLESHOOTING & REPAIR
ACTIVE SCR RECTIFIER ASSEMBLY TEST

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TEST DESCRIPTION
The Active SCR Rectifier Assembly Test will determine if the device is able to be gated
ON and conduct current from anode to cathode.
The Static SCR Rectifier Assembly Test must be performed before proceeding with the
Active SCR Test.

MATERIALS NEEDED

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3/8 in. Nutdriver
5/16 in. Nutdriver
An SCR Tester as specified in this procedure
POWER MIG 255 wiring diagrams (See Electrical Diagrams Section of this Manual)
SCR Heat Sink Assembly Drawings
A volt-ohmmeter

POWER MIG 255

F-23

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F-24

TROUBLESHOOTING & REPAIR

F-24

ACTIVE SCR RECTIFIER ASSEMBLY TEST (continued)
FIGURE F.6 — CONTROL BOARD MOLEX PLUG LOCATIONS FOR G3521 PC CONTROL BOARD.

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J3
J8

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TEST PROCEDURE
1. Disconnect main AC input power to the
machine.
2. Remove the case top and side panels
with a 3/8 in. nutdriver.

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3. Remove the tool tray with a 5/16 in. nutdriver.

POWER MIG 255

TROUBLESHOOTING & REPAIR

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F-25

ACTIVE SCR RECTIFIER ASSEMBLY TEST (continued)
6. Disconnect leads X2 and X3 (braided
copper strap) from the negative capacitor bank buss bar using a 1/2 in. open
end wrench. See Figure F.7.
FIGURE F.7 — LOCATION OF
LEADS X2 AND X3.

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8. Use a commercial SCR tester or construct the tester circuit shown in Figure
F.8. One 6-volt lantern battery can be
used. R1 and R2 resistor values are
±10%. Set voltmeter scale low, at
approximately 0-5 volts or 5-10 volts.
a. Test the voltage level of the battery.
Short leads (A) and (C). Close
switch SW-1. Battery voltage
should be 4.5 volts or higher. If
lower, replace the battery.

NEGATIVE
CAPACITOR
BANK BUSS
BAR

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F-25

FIGURE F.8 — SCR TESTER CIRCUIT
AND SCR CONNECTIONS.

LEADS X2 AND X3
CONNECTION

7. Separate leads X2 and X3 from the
negative capacitor bank buss bar. Be
sure there is no electrical contact.
NOTE: DO NOT DISASSEMBLE THE SCR
RECTIFIER HEAT SINK ASSEMBLY.

POWER MIG 255

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F-26

TROUBLESHOOTING & REPAIR

F-26

ACTIVE SCR RECTIFIER ASSEMBLY TEST (continued)
9. Connect the tester to the SCR 1 as
shown in Figure F.8.

15. Reconnect the tester leads. See Figure
F.8.

a. Connect tester lead (A) to the
anode.

a. Connect tester lead (A) to the
cathode.

b. Connect tester lead (C) to the
cathode.

b. Connect tester lead (C) to the
anode.

c. Connect tester lead (G) to the gate.

c. Disconnect test lead (G) from the
gate.

10. Close switch SW-1.
16. Close switch SW-1.
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NOTE: Switch SW-2 should be open.
17. Read meter for zero voltage.
11. Read meter for zero voltage.
a. If the voltage reading is higher than
zero, the SCR is shorted.
12. Close or keep closed switch SW-1.

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b. If the voltage is higher than zero,
the SCR is shorted.

13. Close switch SW-2 for 2 seconds and
release and read meter.

18. Perform the Active Test Procedure outlined in Steps 6-15 for SCR 2.

a. If the voltage is 3 to 6 volts while
the switch is closed and after the
switch is open, the SCR is
functioning.

19. Replace all SCR assemblies that do not
pass the above tests.

b. If the voltage is 3 to 6 volts only
when the switch is closed or there
is no voltage when the switch is
closed, the SCR is defective.

20. Reconnect plug J6 onto the control PC
board and J9 to the snubber PC board.
21. Reconnect leads X2 and X3 to the negative capacitor bank bus bar.
22. Replace the tool tray and case sides.

NOTE: Be sure battery is functioning properly. A low battery can affect the results of
the test. Repeat Battery Test Procedure in
Step 6 if needed.
14. Open switch SW-1.

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a. If the voltage is zero, the SCR is
functioning.

POWER MIG 255

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F-27

TROUBLESHOOTING & REPAIR
WIRE DRIVE MOTOR AND TACHOMETER FEEDBACK TEST

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TEST DESCRIPTION
This test will determine if the wire drive motor and voltage feedback circuit are functioning properly.

MATERIALS NEEDED
5/16 in. Nutdriver
Volt-Ohmmeter

POWER MIG 255

F-27

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F-28

TROUBLESHOOTING & REPAIR

F-28

WIRE DRIVE MOTOR AND TACHOMETER FEEDBACK TEST (continued)
FIGURE F.9 — PLUG J1 LOCATION ON G3521 PC CONTROL BOARD.

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B J8
(4J1)

#555
(6J1)

W J1
(2J1)

#515B
(5J1)

#206B
(1J1)
J4

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3. Locate plug J1 on the G3521 control
PC board. See Figure F.9.

TEST PROCEDURE
NOTE: POLARITY MUST BE OBSERVED
FOR THESE TESTS.
Test for Correct Wire Drive Motor Armature
Voltage
1. Disconnect main input power to the
machine.

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2. Open the side panels and remove the
tool tray using a 5/16 in. nutdriver.

POWER MIG 255

4. Locate the following leads on plug J1:

LEAD

PLUG
LOCATION

B
W

4J1
2J1

5. Connect the main power to the
machine.

TROUBLESHOOTING & REPAIR

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F-29

WIRE DRIVE MOTOR AND TACHOMETER FEEDBACK TEST (continued)
6. Make the following voltage tests:
a. Turn the machine OFF between
each test.

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FROM
LEAD

TO
LEAD

EXPECTED
VOLTAGE

B
(4J1)

W
(2J1)

3-20 VDC
(varies depending on wire feed
speed)

7. If the voltage to the wire drive motor
armature is zero, check the wires
between plug J1 and the wire drive
motor. Also check the electrical connector J12 for proper connection and contact.
8. If all wires and connectors are good and
the voltage to the drive motor armature
is zero, the G3521 control PC board
may be faulty, replace the control PC
board.
9. If the motor is running at high speed
and the armature voltage is high and
uncontrollable, proceed with the
tachometer test.

TEST FOR SUPPLY VOLTAGE
TO TACHOMETER
1. Disconnect the main AC input power to
the machine.

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2. Locate plug J1 on the G3521 control
PC board. See Figure F.9.
3. Locate the following leads on Plug J1:

b. Carefully insert the meter probes
into the back of each Molex plug
pin cavity to perform the test.
c. Turn the machine ON and pull the
gun trigger to conduct the voltage
test.

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F-29

POWER MIG 255

LEAD

PLUG
LOCATION

515B
206B

5J1
1J1

4. Connect main input power to the
machine.
5. Make the following voltage tests:
a. Turn the machine OFF between
each test.
b. Carefully insert the meter probes
into the back of each Molex plug
pin cavity.
FROM
LEAD

TO
LEAD

EXPECTED
VOLTAGE

515B
(5J1)

206B
(1J1)

15 VDC

6. If the 15 VDC is present, check the
leads to the tachometer circuit.
7. If the leads are okay and 15 VDC is
present, the correct voltage is being
received from the control PC board,
continue with the Supply Voltage to
Tachometer Test.
8. If the 15 VDC is not present and the
leads are okay, the control PC board
may be faulty, replace the control PC
board.

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F-30

TROUBLESHOOTING & REPAIR
WIRE DRIVE MOTOR AND TACHOMETER FEEDBACK TEST (continued)
TEST FOR FEEDBACK VOLTAGE
TO CONTROL BOARD

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c. Turn the machine ON and pull the
gun trigger to conduct the voltage
test.

1. Disconnect the main AC input power to
the machine.

FROM
LEAD

TO
LEAD

EXPECTED
VOLTAGE

2. Locate plug J1 on the G3521 control
PC board.

555
(6J1)

206B
(1J1)

1.5 to 3.5 VDC

3. Locate the following leads on plug J1
(see Figure F.9):

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F-30

LEAD

PLUG
LOCATION

555
206B

6J1
1J1

4. Connect main input power to the
machine.
5. Make the following voltage tests:

6. If the 1.5 to 3.5 VDC is present, the
tachometer circuit is sending the correct feedback signal to the Control PC
Board.
7. If the 1.5 to 3.5 VDC is not present or
not correct, the Control PC Board is
not receiving the proper feedback
voltage from the tachometer circuit.
Check the leads from the tachometer
circuit to the control PC board for loose
or broken connections.

a. Turn the machine OFF between
each test.

8. If the leads are okay, the tachometer
circuit may be faulty, replace the
tachometer circuit.

b. Carefully insert the meter probes
into the back of each Molex plug
pin cavity.

9. Replace the tool tray.

POWER MIG 255

TROUBLESHOOTING & REPAIR

0 VOLTS

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20.0 V

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F-31

NORMAL OPEN CIRCUIT VOLTAGE WAVEFORM

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F-31

2.5 ms

SCOPE SETTINGS
This is a typical DC output voltage waveform
generated from a properly operating Volts/Div . . . . . . . . . . . . . . . . . . 20 V/Div
machine. Note that each vertical division
represents 20 volts and that each horizontal Horizontal Sweep . . . . . . . . . 2.5 ms/Div
division represents 2.5 milliseconds in time.
Coupling . . . . . . . . . . . . . . . . . . . . . . DC
NOTE:
Scope probes connected at
machine output terminals: (+) probe to elec- Trigger . . . . . . . . . . . . . . . . . . . . Internal
trode, (-) probe to work.

POWER MIG 255

TROUBLESHOOTING & REPAIR

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F-32

TYPICAL OUTPUT VOLTAGE WAVEFORM - MACHINE LOADED

0 VOLTS

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F-32

20.0 V

5 ms

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MACHINE LOADED TO 250 AMPS AT 26 VDC
SCOPE SETTINGS
This is a typical DC output voltage waveform
generated from a properly operating Volts/Div . . . . . . . . . . . . . . . . . . 20 V/Div
machine. Note that each vertical division
represents 20 volts and that each horizontal Horizontal Sweep . . . . . . . . . . 5 ms/Div
division represents 5 milliseconds in time.
The machine was loaded with a resistance Coupling . . . . . . . . . . . . . . . . . . . . . . DC
grid bank.
Trigger . . . . . . . . . . . . . . . . . . . . Internal
NOTE: Scope probes connected at machine
output terminals: (+) probe to electrode, (-)
probe to work.

POWER MIG 255

TROUBLESHOOTING & REPAIR

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F-33

ABNORMAL OUTPUT VOLTAGE WAVEFORM - MACHINE LOADED
ONE OUTPUT SCR NOT FUNCTIONING

0 VOLTS

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F-33

20.0 V

5 ms

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MACHINE LOADED TO 220 AMPS AT 22 VDC
SCOPE SETTINGS
This is NOT a typical DC output voltage
waveform. One output SCR is not functioning. Note the increased ripple content. One
SCR gate was disconnected to simulate an
open or non-functioning output SCR. Each
vertical division represents 20 volts and
each horizontal division represents 5 milliseconds in time. The machine was loaded
with a resistance grid bank.

Volts/Div . . . . . . . . . . . . . . . . . . 20 V/Div
Horizontal Sweep . . . . . . . . . . 5 ms/Div
Coupling . . . . . . . . . . . . . . . . . . . . . . DC
Trigger . . . . . . . . . . . . . . . . . . . . Internal

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NOTE: Scope probes connected at machine
output terminals: (+) probe to electrode, (-)
probe to work.

POWER MIG 255

TROUBLESHOOTING & REPAIR

0 VOLTS

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20.0 V

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F-34

ABNORMAL OPEN CIRCUIT VOLTAGE
OUTPUT CAPACITOR BANK NOT FUNCTIONING

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F-34

5 ms

SCOPE SETTINGS
This is NOT the typical DC output voltage
waveform. The output capacitors are not Volts/Div . . . . . . . . . . . . . . . . . . 20 V/Div
functioning. Note the lack of “filtering” in the
output waveform. The output capacitor bank Horizontal Sweep . . . . . . . . . . 5 ms/Div
was disconnected. Each vertical division
represents 20 volts and each horizontal divi- Coupling . . . . . . . . . . . . . . . . . . . . . . DC
sion represents 5 milliseconds in time.
Trigger . . . . . . . . . . . . . . . . . . . . Internal
NOTE: Scope probes connected at machine
output terminals: (+) probe to electrode, (-)
probe to work.

POWER MIG 255

TROUBLESHOOTING & REPAIR

0 VOLTS

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2.00 V

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F-35

TYPICAL SCR GATE VOLTAGE WAVEFORM

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F-35

5 ms

SCOPE SETTINGS
This is a typical SCR gate pulse voltage
waveform. The machine was in an open Volts/Div . . . . . . . . . . . . . . . . . . 2.0 V/Div
circuit condition (no load) and operating
properly. Note that each vertical division Horizontal Sweep . . . . . . . . . . 5 ms/Div
represents 2 volts and each horizontal
division represents 5 milliseconds in time.
Coupling . . . . . . . . . . . . . . . . . . . . . . DC

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NOTE: Scope probes connected at Plug J6 Trigger . . . . . . . . . . . . . . . . . . . . Internal
on the control board. The (+) probe to lead
G2, and the (-) probe to lead 204.

POWER MIG 255

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F-36

NOTES

POWER MIG 255

F-36

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F-37

TROUBLESHOOTING AND REPAIR
CONTROL PC BOARD
REMOVAL AND REPLACEMENT PROCEDURE
WARNING
Service and repair should be performed by only Lincoln Electric factory trained
personnel. Unauthorized repairs performed on this equipment may result in danger
to the technician or machine operator and will invalidate your factory warranty. For
your safety and to avoid electrical shock, please observe all safety notes and precautions detailed throughout this manual.

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CAUTION
Printed Circuit Boards can be damaged by static electricity. Follow static handling
guidelines detailed in “PC Board Troubleshooting Procedures” at the beginning of this
chapter.
------------------------------------------------------------------------------------------------------------------

DESCRIPTION
This procedure will aid the technician in the removal and replacement of the Control PC
Board.

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MATERIALS NEEDED

5/16 in. Nutdriver
Static electricity grounding strap

POWER MIG 255

F-37

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F-38

TROUBLESHOOTING AND REPAIR
CONTROL PC BOARD
REMOVAL AND REPLACEMENT PROCEDURE (Continued)

FIGURE F.10 — WIRING HARNESS
AND MOLEX PLUG LOCATIONS.

REMOVAL AND REPLACEMENT
PROCEDURE
1. Disconnect main input power the
machine.

J5
2. Open the side panels and remove the
tool tray using a 5/16 in. nutdriver.

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J3
J8

3. Disconnect all wiring harness plugs and
Molex plugs connected to the control
board. See Figure F.10.

J4
J2

POWER MIG 255

F-38

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F-39

TROUBLESHOOTING AND REPAIR

F-39

CONTROL PC BOARD
REMOVAL AND REPLACEMENT PROCEDURE (Continued)
FIGURE F.11 — CONTROL BOARD MOUNTING.

TOOL
TRAY

MOUNTING
STANDOFF

PC CONTROL
BOARD

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NOTE: TOP COVER SHOWN
REMOVED FOR CLARITY.
4. Ensure a static electricity grounding
strap is used before handling the control PC boards.

7. When re-installing the control PC board
carefully secure board to mounting
standoffs.

5. Carefully remove the control PC board
from the mounting standoffs.

8. Install all plug connectors previously
removed from the control PC board.

6. Lift the control PC board straight up and
out from the machine.

9. Install the tool tray and close the side
panels.

POWER MIG 255

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F-40

NOTES

POWER MIG 255

F-40

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F-41

TROUBLESHOOTING & REPAIR
WIRE DRIVE ASSEMBLY
REMOVAL AND REPLACEMENT PROCEDURE
WARNING
Service and repair should be performed by only Lincoln Electric factory trained
personnel. Unauthorized repairs performed on this equipment may result in danger
to the technician or machine operator and will invalidate your factory warranty. For
your safety and to avoid electrical shock, please observe all safety notes and precautions detailed throughout this manual.

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DESCRIPTION
This procedure will aid the technician in the removal and replacement of the Wire Drive
Assembly.

MATERIALS NEEDED
Large slot head screwdriver
5/16 in. Nutdriver

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Small slot head screwdriver
3/4 in. Open end wrench
7/16 in. Nutdriver

POWER MIG 255

F-41

TROUBLESHOOTING & REPAIR

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F-42

WIRE DRIVE ASSEMBLY REMOVAL AND REPLACEMENT (continued)
FIGURE F.12 — WIRE DRIVE ASSEMBLY REMOVAL FOR CODES 10563 & 10583 REFER TO P344-F.2
FOR EXPLODED VIEW OF WIRE DRIVE FOR CODES 10986 AND 10990 - SIMILAR PROCEDURE
2
17
9
4

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18
19

1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.

Wire Drive Assembly
Motor/Gearbox Assembly
Flange Nut
Positive Lead
Hose Clamp
Flex Hose
Outer Guide Assembly
Thumb Screw
Adjustment Arm Assembly
Idle Arm
Round Head Screw
Lock Washer
Flat Washer
Molded Drive Roll Shaft
Assembly
Pan Head Screw
Lock Washer
Hex Head Cap Screw
Lock Washer
Flat Washer

7
10
16

8
5

15
6

PROCEDURE
1. Disconnect main input power to the
machine.

3. Lift the wire drive door to gain access to
the wire drive assembly.
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12
11

2. Remove the wire gun and wire.

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4. Lift the tool tray door to allow access to
the tool tray.
5. Use a 5/16 in. nutdriver and remove the
tool tray to gain access to the
motor/gearbox assembly.

POWER MIG 255

6. Disconnect the wire connectors J13
and J12 to the motor/gearbox assembly. See Wiring Diagram.
7. Use a 3/4 in. wrench and remove the
flange nut and positive lead from the
wire drive assembly. See Figure F.12.
8. Use pliers to remove the hose clamp
and flex hose from the wire drive
assembly.
9. Remove the outer guide assembly from
the wire drive assembly by loosening
the thumb screws until the outer guide
can be removed.

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F-43

TROUBLESHOOTING & REPAIR
WIRE DRIVE ASSEMBLY REMOVAL AND REPLACEMENT (continued)
10. Rotate the adjustment arm assembly
counterclockwise to release the tension
on the idle arm.
11. Swing the idle arm up and away from
the wire drive assembly.

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12. Use a screwdriver and remove the
round head screw, lock washer, and flat
washer securing the molded drive roll
shaft assembly to the wire drive assembly.

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F-43

13. Remove the molded drive roll shaft
assembly and the rest of the outer
guide assembly from the wire drive
assembly.
14. Use a screwdriver and remove the pan
head screws and lock washers securing the motor/gearbox assembly to the
wire drive assembly.

POWER MIG 255

15. Grasp the motor/gearbox assembly and
wiggle the motor/gearbox assembly
gently back and forth until it separates
from the wire drive assembly.
16. Use a 7/16 in. nutdriver to remove the
hex head cap screws, lock washers,
and flat washers securing the wire
drive assembly to the wire drive
compartment.
17. Remove the wire drive assembly from
the wire drive compartment.
18. Reassemble the wire drive assembly in
the reverse order.

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F-44

NOTES

POWER MIG 255

F-44

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F-45

TROUBLESHOOTING & REPAIR
SCR OUTPUT RECTIFIER
REMOVAL AND REPLACEMENT PROCEDURE
WARNING
Service and repair should be performed by only Lincoln Electric factory trained
personnel. Unauthorized repairs performed on this equipment may result in danger
to the technician or machine operator and will invalidate your factory warranty. For
your safety and to avoid electrical shock, please observe all safety notes and precautions detailed throughout this manual.

Return to Master TOC

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DESCRIPTION
This procedure will aid the technician in the removal and replacement of the SCR
Assembly.

MATERIALS NEEDED

1/2 in. Open end wrench
1/2 in. Socket wrench, universal tool, and extension

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3/8 in. Nutdriver
3/8 in. Open end wrench

POWER MIG 255

F-45

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F-46

TROUBLESHOOTING & REPAIR
SCR OUTPUT RECTIFIER REMOVAL AND REPLACEMENT (continued)
PROCEDURE
1. Remove the case side panels using a
3/8 in. nutdriver.
2. Disconnect lead #208S and transformer lead X1 from the heat sink on
the left side of the machine using a 1/2
in. socket wrench. See Figure F.13.

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a. Thin lead is always on the outboard
side of the connection.

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F-46

3. Disconnect lead #204 and heavy aluminum choke lead from the middle heat
sink with a 1/2 in. socket wrench and
1/2 in. open end wrench. See Figure
F.14.
4. Remove the diode lead from the negative capacitor band buss bar on the
right side of the machine using a 1/2 in.
socket and 3/8 in. open end wrench.
FIGURE F.14 — MIDDLE HEAT SINK
LEAD DISCONNECTION.

FIGURE F.13 — LEFT HEAT SINK
LEAD DISCONNECTION.

LEFT
HEAT SINK

MIDDLE
HEAT SINK
LEAD X1
LEAD
#208S

POWER MIG 255

HEAVY
LEAD LEAD
#204S

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F-47

TROUBLESHOOTING & REPAIR

F-47

SCR OUTPUT RECTIFIER REMOVAL AND REPLACEMENT (continued)
FIGURE F.15 — RIGHT HEAT SINK LEAD DISCONNECTION.

SCR
ASSEMBLY

SCR DIODE
LEAD

LEAD
#320B

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LEAD
#320

LEAD
#209S
LEAD
X4

5. Remove lead #209S and transformer
lead X4 from the right side heat sink
using a 1/2 in. socket wrench and
1/2 in. open end wrench. See Figure
F.15.
6. Unplug the SCR gate leads G1 and G2
(see wire markers and wiring diagram).
7. Remove the four nuts holding the SCR
assembly to the floor of the machine
using a 3/8 in. nutdriver.

8. Clear the leads and carefully remove
the SCR rectifier assembly.
NOTE: When installing the SCR rectifier
assembly, apply a thin coating of Dow
Corning #340 compound to the electrical
connections.
9. Unplug leads 320 and 320B from the
SCR heat sink thermostat on the right
side at the SCR assembly.

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10. Reassemble the SCR assembly in the
reverse order.

POWER MIG 255

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F-48

NOTES

POWER MIG 255

F-48

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F-49

TROUBLESHOOTING & REPAIR
CAPACITOR BANK
REMOVAL AND REPLACEMENT PROCEDURE
WARNING
Service and repair should be performed by only Lincoln Electric factory trained
personnel. Unauthorized repairs performed on this equipment may result in danger
to the technician or machine operator and will invalidate your factory warranty. For
your safety and to avoid electrical shock, please observe all safety notes and precautions detailed throughout this manual.

Return to Master TOC

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WARNING
The liquid electrolite in the capacitors is toxic. Do not touch the capacitors with
any part of your body.
-------------------------------------------------------------------------------------------------------------------

DESCRIPTION
This procedure will aid the technician in the removal and replacement of the Capacitor
Bank.

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MATERIALS NEEDED

5/16 in. Nutdriver
3/8 in. Nutdriver
1/2 in. Open end wrench
3/8 in. Open end wrench
Wiring diagram

POWER MIG 255

F-49

TROUBLESHOOTING & REPAIR

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F-50

CAPACITOR BANK REMOVAL AND REPLACEMENT (continued)
FIGURE F.16 — LOCATION OF CAPACITOR BANK REMOVAL AND REPLACEMENT COMPONENTS.

LEAD
#206

SCR DIODE
LEAD

CAPACITOR
BANK
LEAD
#206B

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SHUNT
LEADS
X1 AND X2

POWER
ENHANCEMENT
CHOKE LEAD

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OUTPUT
CHOKE LEAD

tive capacitor bank buss bar using a
1/2 in. open end wrench.

PROCEDURE
See Figure F.16 for location of capacitor
bank removal and replacement components.
1. Disconnect main input power to the
machine.
2. Remove the case side panels using a
3/8 in. nutdriver.

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3. Test that the capacitors are discharged
using a volt ohmmeter. Polarity must
be observed.
4. Remove the two transformer secondary
leads X2 and X3 (braided copper strap)
from the negative capacitor bank buss
bar using two 1/2 in. open end wrenches.
5. Remove the shunt, leads 206, 206B,
and the SCR diode lead from the nega-

POWER MIG 255

6. Remove the choke lead and lead 204B
from the positive capacitor bank buss
bar using two 1/2 in. open end wrenches.
7. Remove the power factor enhancement
choke lead from the positive capacitor
buss bar using two 1/2 in. open end
wrenches.
8. Remove the three nuts holding the
capacitor bank to the floor of the
machine using a 3/8 in. nut driver.
9. Clear the leads and carefully remove
the capacitor bank assembly from the
machine.
10. Reassemble the capacitor bank in the
reverse order.

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F-51

TROUBLESHOOTING & REPAIR
MAIN TRANSFORMER AND OUTPUT CHOKE
REMOVAL AND REPLACEMENT PROCEDURE
WARNING
Service and repair should be performed by only Lincoln Electric factory trained
personnel. Unauthorized repairs performed on this equipment may result in danger
to the technician or machine operator and will invalidate your factory warranty. For
your safety and to avoid electrical shock, please observe all safety notes and precautions detailed throughout this manual.

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DESCRIPTION
This procedure will aid the technician in the removal and replacement of the Main
Transformer and Choke Assembly.

MATERIALS NEEDED

5/16 in. Nut Driver
1/2 in. Open end wrench
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3/8 in. Open end wrench
1/2 in. Socket wrench, extender, universal adapter
Wire cutters
Phillips head screwdriver

POWER MIG 255

F-51

TROUBLESHOOTING & REPAIR

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F-52

MAIN TRANSFORMER AND OUTPUT CHOKE
REMOVAL AND REPLACEMENT (continued)
FIGURE F.17 — MAIN TRANSFORMER REMOVAL.

LEAD
X1

OUTPUT
CHOKE
LEAD

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OUTPUT
CHOKE
POSITIVE
LEAD

NOTE: PLUG-IN LEADS ARE
NOT SHOWN FOR
CLARITY.
LEAD
X4
LEADS
X2 AND X3

MAIN
TRANSFORMER

POWER
ENHANCEMENT
CHOKE

PROCEDURE
1. Disconnect main input power to the
machine.
2. Remove the case side panels using a
3/8 in. nutdriver.

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3. Test that the capacitors are discharged
using a volt ohmmeter. Polarity must
be observed.

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F-52

4. Remove lead X1 from the left side SCR
heat sink assembly using a 1/2 in. socket wrench, extender and universal
adapter. See Figure F.17.
5. Remove lead X4 from the right side
heat sink assembly using a 1/2 in. socket wrench, extender and universal
adapter.

POWER MIG 255

6. Remove the two transformer secondary
leads X2 and X3 (braided copper strap)
from the negative capacitor bank buss
bar using two 1/2 in. open end wrenches.
7. Disconnect and label all transformer
leads from the reconnect panel using a
3/8 in. open end wrench.
8. Disconnect and label all leads from the
input power switch.
9. Remove the power switch.
10. Disconnect thermostat leads #320 and
#320B from the SCR Rectifier.

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F-53

TROUBLESHOOTING & REPAIR
MAIN TRANSFORMER AND OUTPUT CHOKE
REMOVAL AND REPLACEMENT (continued)

11. Unplug and label leads X5, X6, X7, X8, and X9.
These leads have connectors near the transformer which can be disconnected.

14. Remove the four nuts and washers mounting the
transformer to the floor of the machine using a
1/2 in. wrench.

12. Disconnect the output choke lead from the positive capacitor bank buss using two 1/2 in. open
end wrenches.

15. Carefully remove the main transformer and choke
assembly.

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13. Remove the other output choke lead from the
positive output terminal using a 1/2 in. wrench.

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F-53

16. Reassemble the main transformer and choke
assembly in the reverse order.

13. Remove all cable ties, wire mounts, and any harness type that could get in the way during transformer removal using wire cutters and screw
driver.

POWER MIG 255

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F-54

NOTES

POWER MIG 255

F-54

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F-55

TROUBLESHOOTING & REPAIR
FAN MOTOR ASSEMBLY
REMOVAL AND REPLACEMENT PROCEDURE
WARNING
Service and repair should be performed by only Lincoln Electric factory trained
personnel. Unauthorized repairs performed on this equipment may result in danger
to the technician or machine operator and will invalidate your factory warranty. For
your safety and to avoid electrical shock, please observe all safety notes and precautions detailed throughout this manual.

Return to Master TOC

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DESCRIPTION
This procedure will aid the technician in the removal and replacement of the Fan Motor
Assembly.

MATERIALS NEEDED

3/8 in. Nutdriver
11/32 in. Open end wrench
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Slot head screwdriver

POWER MIG 255

F-55

TROUBLESHOOTING & REPAIR

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F-56

FAN MOTOR ASSEMBLY REMOVAL AND REPLACEMENT (continued)
FIGURE F.18 — FAN MOTOR ASSEMBLY REMOVAL.

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FAN
BLADE

LEAD
#353

LEAD
#352

FAN
MOTOR

PROCEDURE
1. Disconnect main input power to the
machine.
1. Remove the case side panels using a
3/8 in. nutdriver.
2. Disconnect the fan motor leads #352
and #352. See Figure F.18.

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3. Remove the fan blade. Note the position of the fan on the shaft for reassembly.
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F-56

a. Use a screwdriver to loosen the fan
blade clamp.
b. Slide the fan blade off the motor
shaft.
4. Remove the fan motor.

POWER MIG 255

FAN
BLADE
CLAMP

a. Loosen and remove the two nuts
and lock washers from the motor
mounting bracket using a 11/32 in.
open end wrench.
b. When the motor is free from the
mounting bracket, slide the motor
from the POWER MIG unit.
5. Install the replacement motor in the
reverse order of removal.
6. Install the fan blade and tighten the fan
blade clamp. Ensure the fan is in the
same position on the shaft as it was
prior to removal.
a. Spin the fan to be sure it is free to
rotate.
7. Reassemble the remaining components in reverse order of removal.

TROUBLESHOOTING AND REPAIR

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F-57

RETEST AFTER REPAIR
INPUT IDLE AMPS AND WATTS
Input Volts/Hertz

Maximum Idle Amps

Maximum Idle Watts

230/60

7.0

400

OPEN CIRCUIT VOLTAGE

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35-40 VDC

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F-57

WIRE SPEED RANGE
50 - 700 IPM (1.27 - 17.8 m/minute)

POWER MIG 255

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F-58

NOTES

POWER MIG 255

F-58

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Section G-1

TABLE OF CONTENTS
- ELECTRICAL DIAGRAMS SECTION -

Section G-1

Electrical Diagrams ...............................................................................................Section G

Wiring Diagram - Entire Machine - Code 10563 - (L10979) . . . . . . . . . . . . . . . . . . . .G-2
Wiring Diagram - Entire Machine - Code 10583 - (L10980) . . . . . . . . . . . . . . . . . . . .G-3
Wiring Diagram - Entire Machine - Code 10986 - (L11980) . . . . . . . . . . . . . . . . . . . .G-4
Wiring Diagram - Entire Machine - Code 10990 - (L11979) . . . . . . . . . . . . . . . . . . . .G-5
Control PC Board Schematic (G3520-1D1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .G-6

Display PC Board Schematic (L10951) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .G-8
Display PC Board Assembly (L10952-1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .G-9
Snubber PC Board Schematic (S24374) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .G-10
Snubber PC Board Assembly (M19248-1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .G-11

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Control PC Board Assembly (G3521-1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .G-7

POWER MIG 255

WIRING DIAGRAM - ENTIRE MACHINE - CODE 10563 - (L10979)

POWER MIG 255 (208/230V)
NOTES:

GENERAL INFORMATION

515

256

J13
3

253

254

251

Return to Master TOC

392

265
263
262

264
260

515B

261

206B

**
2

SNUBBER

324

BOARD

X5
14.2V
X6
14.2V
X7
L1

209R

J12

8
9

206B

B
H1
LINE
SWITCH
S1

204S

204

325

324

208

208R

204S

209S

209

209R

ASBLY

J13

SCR 2

X4
209S

515B

555

206B

POWER
TRANSFORMER

TO GROUND PER
NATIONAL ELECTRICAL
CODE

SCR HEATSINK
ASSEMBLY
THERMOSTAT

T
A
C
H

P.M.

390
392

325B

SCR HEATSINK

208S

320

320B

555

208S

515B

28.4V

X2
H2

208V

RECONNECT
PANEL

SCR 1

TO SINGLE PHASE
SUPPLY LINE

R.F.
CHOKE
AS’BLY

208R

D2
BAFFLE
MOUNTED
RECTIFIER
DIODE
BRIDGE

28.4V

230V

116.6V
X9

325

354

5
6

3
4

325

FOR SPOOL GUN OPTION

9
10

1
2

FOR TIMER
OPTION

J11

1
2

9
10

555

SECONDARY VOLTAGES SHOWN
ARE NO LOAD RMS VALUES

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390

WIRE FEED
SPEED

267

Return to Section TOC

252

GAS
SOLENOID

324

5
6

ARC
VOLTAGE

11
R4

J11

J12

GUN
TRIGGER

13
2

Return to Section TOC

254
500

J10
10

550

254A

(NON-LEAD SIDE OF CONNECTOR)
9

353

CAVITY
NUMBERING SEQUENCE

J5
8

551
256

500

515

552

INDICATES CONNECTOR CAVITY NO.
6

550

CONDUCTOR STRAP AND WORK STUD.

251

FAN
MOTOR

OFF AND REVERSE LEAD CONNECTIONS AT CABLE

U - BLUE

551

252

"POSITIVE". TO CHANGE POLARITY, TURN THE UNIT

R - RED

253

N.B. THIS DIAGRAM SHOWS THE "ELECTRODE" POLARITY

B - BLACK

552

CONTROL BOARD
352

FUTURE APPLICATIONS.

W - WHITE
1
1

BOARD

CURRENT AND DUTY CYCLE OF IMMEDIATE AND

COLOR CODE:

(COMPONENT SIDE OF P.C. BOARD)

DISPLAY

CAVITY NUMBERING SEQUENCE

J10

N.A. WELDING CABLE MUST BE OF PROPER CAPACITY FOR THE

ELECTRICAL SYMBOLS PER E1537

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G-2

ELECTRICAL DIAGRAMS

Return to Section TOC

G-2

OUTPUT CHOKE
THERMOSTAT

SCI

325A

543
326

3
4
5

541A

SCI

8
515

206A

10
11
12

MOTOR/
GEARBOX

209
208

TO
WORK

206
206S
205

352
X9

3
4
5
6
7
8

354

325B

GND
320
206

1
2

207

11
12
13
14

206S

207

+
-

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POWER FACTOR
ENHANCEMENT
CHOKE

C3
+

C1 THRU C3
31,000 MFD
50V

G2
204

C2
+

X8
205

206B
C1

353

15 OHMS
100 W

X7
X6

204B

1
2
3

4
5
6

OUTPUT
CHOKE

R.F. FILTER

GND

2-23-2001A
L10979

NOTE: This diagram is for reference only. It may not be accurate for all machines covered by this manual. The wiring diagram specific to your code is pasted inside one of the enclosure panels of your machine.
POWER MIG 255

WIRING DIAGRAM - ENTIRE MACHINE - CODE 10583 - (L10980)

POWER MIG 255 (230/460/575V)
NOTES:

GENERAL INFORMATION

CAVITY NUMBERING SEQUENCE

256

J13

J12

253

254

251

390

WIRE FEED
SPEED

392

325

H2
H5

4
H4

9
10

204

208S
208

206B

J12
-

208R

209

209R

320

320B

28.4V
204S

325B

SCR HEATSINK

SCR HEATSINK
ASSEMBLY
THERMOSTAT

ASBLY

J13

SCR 2

515B

G2
209S

555

206B

POWER
TRANSFORMER

1
2
3
4

T
A
C
H

P.M.

392

208S

555

390

204S
209S

OUTPUT CHOKE
THERMOSTAT

7
8

1
2

SCI

325A

543

326

541A

SCI

5
J3

8
515

206A

10
11
12

209
208

TO
WORK

206
206S

205

1
2
3
4
5
6

352
X9
354
325B

206

11
12
13

207

+
-

POWER FACTOR
ENHANCEMENT
CHOKE

C3
+

C1 THRU C3
31,000 MFD
50V

14
15
16

205

206B
C1

8
9
10

320

X8
206S

GND

353

Return to Master TOC

MOTOR/
GEARBOX

TO GROUND PER
NATIONAL ELECTRICAL
CODE

Return to Section TOC

515B

325
324

H1
LINE
SWITCH
S1

X9
X5

208R

209R

D2
BAFFLE
MOUNTED
RECTIFIER
DIODE
BRIDGE

TO SINGLE PHASE
SUPPLY LINE

FOR TIMER
OPTION

R.F.
CHOKE
AS’BLY

28.4V

RECONNECT
PANEL
(SHOWN CONNECTED
FOR 230V)

SCR 1

6
7

BOARD

14.2V
X7

261

324

14.2V
X6

206B

SNUBBER

264

325

116.6V
X9

267

SECONDARY VOLTAGES SHOWN
ARE NO LOAD RMS VALUES

262

555

263

265

260

515B

J11

FOR SPOOL GUN OPTION

Return to Master TOC

252

GAS
SOLENOID

8
9
10
11
12

515

354

Return to Master TOC

254
500

ARC
VOLTAGE

324

5
6
7

J11
1

13
1

Return to Section TOC

256

254A

(NON-LEAD SIDE OF CONNECTOR)

J10

GUN
TRIGGER

550

** CAVITY
NUMBERING SEQUENCE
2

Return to Section TOC

500

515

251
552

353

252

551

INDICATES CONNECTOR CAVITY NO.

550

CONDUCTOR STRAP AND WORK STUD.

J2
12

FAN
MOTOR

OFF AND REVERSE LEAD CONNECTIONS AT CABLE

R - RED

551

253

"POSITIVE". TO CHANGE POLARITY, TURN THE UNIT

U - BLUE
6

CONTROL BOARD
352

N.B. THIS DIAGRAM SHOWS THE "ELECTRODE" POLARITY

W - WHITE

552

J7
5

J1
J9

1
1
2

BOARD

FUTURE APPLICATIONS.

B - BLACK

DISPLAY

CURRENT AND DUTY CYCLE OF IMMEDIATE AND

COLOR CODE:

(COMPONENT SIDE OF P.C. BOARD)

J10

N.A. WELDING CABLE MUST BE OF PROPER CAPACITY FOR THE

ELECTRICAL SYMBOLS PER E1537

Return to Master TOC

G-3

ELECTRICAL DIAGRAMS

Return to Section TOC

G-3

15 OHMS
100 W

204B

204

X6
X5

OUTPUT
CHOKE

R.F. FILTER

GND

2-23-2001A
L10980

POWER MIG 255 (230/460/575 V)
NOTES:

GENERAL INFORMATION

CAVITY NUMBERING SEQUENCE

COLOR CODE:

(COMPONENT SIDE OF P.C. BOARD)
3

J1
J9
J12

J6
4

J4
J7

J2
7

B - BLACK
W - WHITE
R - RED
U - BLUE
INDICATES CONNECTOR CAVITY NO.

(NON-LEAD SIDE OF CONNECTOR)

Return to Master TOC

3 4

254

252

251

390

WIRE FEED
SPEED

392

265
263
262
267
264
260
261

324

325

J11

J12

324

14.2V
X6

354
D2
BAFFLE
MOUNTED
RECTIFIER
DIODE
BRIDGE

H2
H5

H1
3

4
5
6
7
8

515B
555
206B

204
208S
208
208R
204S
209S
209
209R

1
2
3
4
5
6
7
8

B
W

X6
208S

320

28.4V

204S

320B
W

SCR HEATSINK
ASBLY

325B

B
SCR HEATSINK
ASSEMBLY
THERMOSTAT

SCR 2

R
U
B

G2
209S

POWER
TRANSFORMER

T
A
C
H

OUTPUT CHOKE
THERMOSTAT

206B
B

1
2
3

W
515B
555
325
324

4
5
6
7
8

390
392

1
2

SCI
325A
543
326

1
2
3

541A
SCI
515
206A

209
208
206
206S
205

TO
WORK

352
X9
354
325B
GND
320
207

TO GROUND PER
NATIONAL ELECTRICAL
CODE

206

353
X8
206S 205

207

G2
204
G1
X7
X6
X5

206B
C2

C1
+

POWER FACTOR
ENHANCEMENT
CHOKE

C3
+

Return to Master TOC

+
-

Return to Section TOC

4
5
6
7
8
9
10
11
12

WIRE
DRIVE
MOTOR/
GEARBOX

W
TO SINGLE PHASE
SUPPLY LINE

B
W

1
2
3

28.4V

LINE
SWITCH
S1

208R

209R

RECONNECT
PANEL
(SHOWN CONNECTED
FOR 230V)

14.2V
X7
X1

X8
X9
X5

R
U
B

SNUBBER
BOARD

SCR 1

4
5
6
7
8
9
10

116.6V
X9
X5

4
5
6
7
8
9
10

325

1
2
3

6
7
8
9
10
11
12
13
14

1
2
3

FOR TIMER
OPTION

1
2
3
4
5

GAS
SOLENOID

GUN
TRIGGER

550
254
500

ARC
VOLTAGE

SECONDARY VOLTAGES SHOWN
ARE NO LOAD RMS VALUES

Return to Master TOC

253

Return to Section TOC

FAN
MOTOR

515
256

J11

253
252
251
552
551
256

254A
R4

1 2

J10

CONTROL BOARD
352

353

N.B. THIS DIAGRAM SHOWS THE "ELECTRODE" POLARITY
"POSITIVE". TO CHANGE POLARITY, TURN THE UNIT
OFF AND REVERSE LEAD CONNECTIONS AT CABLE
CONDUCTOR STRAP AND WORK STUD.

CAVITY
NUMBERING SEQUENCE

DISPLAY
BOARD

500
515
550
551
552

J10

N.A. WELDING CABLE MUST BE OF PROPER CAPACITY FOR THE
CURRENT AND DUTY CYCLE OF IMMEDIATE AND
FUTURE APPLICATIONS.

ELECTRICAL SYMBOLS PER E1537

FOR SPOOL GUN OPTION

Return to Master TOC

WIRING DIAGRAM - ENTIRE MACHINE - CODE 10986 - (L11980)

Return to Section TOC

G-4

ELECTRICAL DIAGRAMS

8
7
6
5
4
3
2

Return to Section TOC

G-4

C1 THRU C3
31,000 MFD
50V

15 OHMS
100 W

204B

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1
2
3
4
5
6

OUTPUT
CHOKE

R.F. FILTER

GND

A
L11980

POWER MIG 255 (208/230 V)
NOTES:

GENERAL INFORMATION

CAVITY NUMBERING SEQUENCE

COLOR CODE:

(COMPONENT SIDE OF P.C. BOARD)
3

J1
J9
J12

J6
4

J4
J7

J2
14

N.B. THIS DIAGRAM SHOWS THE "ELECTRODE" POLARITY
"POSITIVE". TO CHANGE POLARITY, TURN THE UNIT
OFF AND REVERSE LEAD CONNECTIONS AT CABLE
CONDUCTOR STRAP AND WORK STUD.

B - BLACK
W - WHITE
R - RED
U - BLUE
INDICATES CONNECTOR CAVITY NO.

Return to Master TOC

254

252

251

ARC
VOLTAGE

324

325

J11

390

WIRE FEED
SPEED

392

265
263
262
267
264
260

J12

324

116.6V
X9
X5
14.2V
X6

L1
H2

14.2V
X7
X1

X8
X9
X5

230V 208V
W

RECONNECT
PANEL

4
5
6
7
8

B
W

320

204S

320B
W

SCR HEATSINK
ASBLY

325B

B
SCR HEATSINK
ASSEMBLY
THERMOSTAT

SCR 2

OUTPUT CHOKE
THERMOSTAT

R
U
B

G2
209S

H3
POWER
TRANSFORMER

TO GROUND PER
NATIONAL ELECTRICAL
CODE

T
A
C
H

206B
B

1
2
3

W
515B
555
325
324

4
5
6
7
8

390
392

1
2

SCI
325A
543
326

1
2
3

541A
SCI
515
206A

209
208
206
206S
205

TO
WORK

352
X9
354
325B
GND
320
207
353
X8

206S 205
+
-

207

G2
204
G1
X7
X6
X5

206B
C2

C1
+

POWER FACTOR
ENHANCEMENT
CHOKE

C3
+

Return to Master TOC

4
5
6
7
8
9
10
11
12

WIRE
DRIVE
MOTOR/
GEARBOX

206

Return to Section TOC

28.4V
H1

LINE
SWITCH
S1

515B
555
206B

204
208S
208
208R
204S
209S
209
209R

1
2
3

208S

28.4V

4
5
6
7
8

SCR 1

B
W

1
2
3

SNUBBER
BOARD

TO SINGLE PHASE
SUPPLY LINE

4
5
6
7
8
9
10

208R

209R

D2
BAFFLE
MOUNTED
RECTIFIER
DIODE
BRIDGE

R
U
B

SECONDARY VOLTAGES SHOWN
ARE NO LOAD RMS VALUES

4
5
6
7
8
9
10

325

1
2
3

FOR TIMER
OPTION

**
2

6
7
8
9
10
11
12
13
14

1
2
3

1
2
3
4
5

261

354

Return to Master TOC

253

GAS
SOLENOID

GUN
TRIGGER

550
254
500

515
256

J11
3 4

Return to Section TOC

FAN
MOTOR

(NON-LEAD SIDE OF CONNECTOR)

253
252
251
552
551
256

254A

1 2

J10

CONTROL BOARD
352

353

CAVITY
NUMBERING SEQUENCE

J5
8

DISPLAY
BOARD

500
515
550
551
552

J10

N.A. WELDING CABLE MUST BE OF PROPER CAPACITY FOR THE
CURRENT AND DUTY CYCLE OF IMMEDIATE AND
FUTURE APPLICATIONS.

ELECTRICAL SYMBOLS PER E1537

FOR SPOOL GUN OPTION

Return to Master TOC

WIRING DIAGRAM - ENTIRE MACHINE - CODE 10990 - (L11979)

Return to Section TOC

G-5

ELECTRICAL DIAGRAMS

8
7
6
5
4
3
2

Return to Section TOC

G-5

C1 THRU C3
31,000 MFD
50V

15 OHMS
100 W

204B

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1
2
3
4
5
6

OUTPUT
CHOKE

R.F. FILTER

GND

A
L11979

Return to Master TOC

ELECTRICAL DIAGRAMS

G-6

CONTROL PC BOARD SCHEMATIC - (G3520-1D1)

Return to Master TOC
Return to Master TOC

Return to Master TOC

Return to Section TOC
Return to Section TOC

Return to Section TOC

G-6

NOTE:

Lincoln Electric assumes no responsibility for liablilities resulting from board level troubleshooting. PC Board repairs will invalidate your factory warranty. Individual Printed Circuit Board Components are not available
from Lincoln Electric. This information is provided for reference only. Lincoln Electric discourages board level troubleshooting and repair since it may compromise the quality of the design and may result in danger to the
Machine Operator or Technician. Improper PC board repairs could result in damage to the machine.

POWER MIG 255

CONTROL PC BOARD ASSEMBLY - (G3521-1)
3521-1

Return to Master TOC

G-7

ELECTRICAL DIAGRAMS
G

Return to Section TOC

G-7

ITEM

REQ’D

PART NO.

IDENTIFICATION

S16668-5

C1,C2,C8,C9,C14,C20,C29

.022/50

C36,C37,C38,C39,C43,C44
C48,C52,C53,C55,C56
C3,C4,C11

C5,C6,C18,C19,C35,C51,C54

C10,C22,C23,C24,C25,C30

S13490-42

1.0/35

T11577-52

.0047 OR .005/1400

S13490-73

20/50

S16668-11

.1/50

C31,C32,C33,C34,C40,C41
C45,C46,C57,C58

~.04

C12,C13

C15

C16

C17,C28

C26

C27

C47

C49

C50

C59

D1,D2,D3,D31

S16668-1

39/10

S13490-92

3300/50

S13490-39

18/15
.22/100

T11577-28
S13490-118

2200/63V

S16668-7
S13490-76

820pF/50
.001/400

S13490-102

.047/100

S24833-1

0.27/63V

T12199-2

1N4007

T12199-1

D4,D5,D6,D7,D8,D9,D10,D11,D12,D13,D14, 31

6.00

22pF/100

S13490-30

1N4004

D15,D16,D17,D18,D19,D20,D21,D22,D24
D25,D26,D27,D28,D29,D30

Return to Master TOC

C4
R20

R117

CONTROL G3521-1

R25

R64

R59

R66

R67

R49

C26

R114

R18

D11

R26

R14

R23

OCI1

D10

R27

R15

R80

R24

R94

R13

R22

OCI2

D37

Q4
R81

L1,L2,L3,L4

OCI1,OCI2

OCI3

Q1,Q2,Q3,Q6,Q11

Q5,Q9

Q7,Q10

R1,R2,R6,R41,R42,R65,R75

R3,R7,R25,R26,R114,R117

R4,R51

R5,R9,R12,R30,R35,R45,R70

R10,R11,R62,R63,R76,R77

R18,R20,R24,R80

R108

R19,R21,R58,R83

R109

R28,R46,R61

C52

R29,R100,R110

R31,R106

R32

R33,R37,R38

R96

TRI1

R97

1N4735

T12702-45

1N4746A

S18248-8

HEADER

S18248-14

HEADER

S18248-12

HEADER

S24020-10

HEADER,VERTICAL

S18248-16

HEADER

S18248-6

HEADER

S18248-2T

HEADER

T12218-7

330uH

S15000-30

OPTOCOUPLER TRIAC DRIVER 800V

S15000-31

OPTOCOUPLER,TRIACDRV,RANDOM,800V

T12704-68

2N4401

S18105-4

HEATSINK ASBLY

T12704-35

NPN TRANSISTOR

T12704-88

TRANSISTOR,NMF,T220,45A,100V(SS)

T12704-69

2N4403

S19400-1002

10K 1/4W

S24002-1200

120 2.5W

S19400-1502

15K 1/4W

S19400-4751

4.75K

S19400-1211

7/16W

1.21K 1/4W

S19400-1000

100 1/4W
1.21K 1/4W

TP2

TP1

C51
C54

C35

TP7

TP3

C18 C19

9.00

~.04

8.80

Ch’ge. Sht. No.

R34,R40

R36

R39,R68,R71,R72,R91,R92

XE-RW

R43

R44,R109

R47

R48

R49,R50

R52,R98

R53

R54

R55,R56

R57,R108

R59,R66,R69,R73,R74,R86,R87

R60

R64,R67

R81

R88,R89

R96,R103

R97

R99

R101,R102

R104

R107

R116

TP1,TP2

TP3,TP4

TP7

TRI1

X4,X5

X10,X11

X12

11-16-2001D
A

3-12-99

S19400-6810

681 1/4W

S19400-15R0

15 1/4W

S19400-5620

562 1/4W

S19400-2211

2.21K 1/4W

S19400-6811

6.81K 1/4W

S19400-1501

1.5K 1/4W

S19400-5621

5.62K 1/4W

S19400-2672

26.7K 1/4W

S19400-2212

22.1K 1/4W

S19400-33R2

33.2 1/4W

S19400-2671

2.67K 1/4W

S19400-3321

3.32K 1/4W

S19400-1004

1M 1/4W

S19400-1001

1K 1/4W

S19400-1301

1.3K 1/4W

S19400-2801

2.8K 1/4W

T14648-22

50 5W

3.01K 1/4W
.25 OHM, 7W RESISTOR

S19400-5111
T12300-75

5.11K 1/4W

S19400-26R7

26.7 1/4W

S19400-2670

267 1/4W

S19400-4422

44.2K 1/4W

S19400-2432

24.3K 1/4W

S19400-5110

511 1/4W

T14648-5

3.3K 5W

S19400-1622

16.2K 1/4W

S19400-4752

47.5K 1/4W

T14648-19

1K 5W

S19400-1652

16.5K 1/4W

S19400-1372

13.7K 1/4W

S19400-7500

750 1/4W

S19400-4750

475 1/4W

S19400-2802

28.0K 1/4W

T13640-15

15J

T13640-9

20J

T13640-18

MOV,120J

S15161-27

T2500D
ROM ASSEMBLY (SS)

S24392-4
M15102-3

IC,S8054HN,CMOS,UNDERVOT-SENSING(SS)

S17900-8

14 PINI.C.(SS)

S15128-11

14 PIN QUAD COMPARATOR

S15128-16

IC,LT1014,LINEAR INTEGRATED CIRCUIT

S23060-1

IC,SWITCH,LO-SIDE(SS)

S15018-4

MC14584(SS)

S15018-6

DIGITAL INTEGRATED CIRCUIT(SS)

S15128-10

IC,431,VOLTAGE REF.

S15128-5

+5V REG.

S16665-5

8.0 MHZ

EQUIP.

POWER MIG 255

TYPE

CLEVELAND, OHIO U.S.A.
SCALE

7-28-2000J
10-5-2001C

S19400-3011

THE LINCOLN ELECTRIC CO.

7-9-99H

NOTE:

1N5818

T12702-40

4.75K

R8,R115

R14,R15,R23,R27

C45

TP4

C27
R8

R115

T12705-23

R78,R82,R95,R105

D28

R13,R22,R93,R94

Return to Section TOC

DZ2,DZ3,DZ4

R90

R10

R11

C50

C24

R98

R71

R74

C25

R72

D27

R73

C29

R83

DZ4

3.20

DZ1

R79,R84,R112,R113

.20

D23,D37

R111

C48

R105

DZ3

R54
J2

D26

R78
R88

R76

R92

R87
R89

D30

Q10

C47

C46

D33

D35

R101

C23

R68

R69

C43

R95

D34

R100
R75

D22

D21

R70

C22

C31
R91

Q1
Q2
R50

X11

D25

X10
C1

R107

D36

D32

R82

C41
C30

R77

R79

D23
R48

C53

R99

R86

Q11

C28

DZ1

D15

R55

R56

R51

R52

DZ2

C16

R53

R111

XXXXXXXXXXXXXXXX
C40

R110

R12

.20

R93

R21

C56

C57

C58

D14

X
XXXXXXXXXXXXXX

R90

R45

R44

C10

C14

D18

R61

X12

XXXXXXXXXXXXXXX

Return to Master TOC

C55

D29

D13
D17

R63

R58

C20

D19

D20

R62

XXXXXXXXXXXXX

R35

C13

R113

R65

R116
R60

D16

C34

C32

R33

X5
C8

R29

R30

R39

C11

R46

R28

R106

R43

C12

R84

D24
R41

C33

C49
X9

R103

R102

C38

C37

C39

R42

D12

R31

R32

R1
C2

C44

R57

R36
D31

C15

C17

R37

R47

Return to Master TOC

Return to Section TOC

R104

C36

Return to Section TOC

R40

OCI3

R38

R34

R19
R112

D32,D33,D34,D35,D36

5.80

DR C.S./

SUBJECT

FULL

DATE 12-18-98

CHK

REF.

CONTROL P.C. BOARD ASSEMBLY
G2803-1

SHT.
SUP’S’D’G

NO.

3521-1

POWER MIG 255

G-8

ELECTRICAL DIAGRAMS

/ENABLE
DATA OUT

7
9

DISP1

R11

L 10951
SHT.
NO.
SUP’S’D’G.

POWERMIG 255

SCHEMATIC, DISPLAY PCB

EARTH GROUND CONNECTION

COMMON CONNECTION

FRAME CONNECTION

VOLTAGE NET

POWER SUPPLY SOURCE POINT

CHK.

1.50K

DR.

MC14489

SUPPLY

DISP- 7

LED- 3
10

D-

C-

6
DISP2

NONE

CLOCK

DISP3

2/20/98

Vss

DATE

Return to Master TOC

Return to Section TOC

DATA IN

GENERAL INFORMATION

SCALE

TYPE

BANK5

3
1

SUBJECT

BANK1

CLEVELAND, OHIO U.S.A.

THE LINCOLN ELECTRIC CO.

EQUIP.

FILENAME: L10951-1AB

BANK2

(UNLESS OTHERWISE SPECIFIED)

3
1

1A, 400V

DIODES =

UNLESS OTHERWISE SPECIFIED)

Vdd

1/4W

MFD ( .022/50V

CAPACITORS =

BANK3

ELECTRICAL SYMBOLS PER E1537

BANK4

RESISTORS = Ohms (

500

UNLESS OTHERWISE SPECIFIED)

LABELS

R-

X- 5

DISPLAY PC BOARD SCHEMATIC - (L10951)

LAST NO. USED

Return to Master TOC

Return to Section TOC

G-8

50V
500

Return to Master TOC

SCK

R9
475

500

.0047
50V

J10

MOSI

10K

475

C7
.0047
50V

BANK4

BANK3

Vdd

3
1
2

BANK2

BANK1

BANK5

DATA IN

/ENABLE

500

Vss

CLOCK

5
6
7
9

DATA OUT

DISP7

7
9
10

DISP6

7
9

VOLTS
LED3

DISP5

NOTES :

500

Return to Section TOC

J10
5

MC14489

N.A.

.0047

SINCE COMPONENTS OR CIRCUITRY ON A PRINTED CIRCUIT BOARD MAY CHANGE

3-12-99

475

Ch’ge.Sht.No.

R10

NUMBER.

LATCH

NOT SHOW THE EXACT COMPONENTS OR CIRCUITRY OF CONTROLS HAVING A COMMON CODE

J10
4

WITHOUT AFFECTING THE INTERCHANGEABILITY OF A COMPLETE BOARD, THIS DIAGRAM MAY

500

R12

1.50K

500

R1
221
500

R2
221
R13

+5VA

221
D1

Return to Master TOC

515

Vdd

221
X1

R14

221
C1
4.7
35V

L 10951

Return to Section TOC

221

J10

7805

C10

OUT

50V

0.1

0.1
MC14489

GND

MC14489

50V

HEXINV

0.1

50V

C2
18
15V

Vss

J10

500

NOTE:

POWER MIG 255

4.7/35

S13490-39

18/15

C3,C4,C10

S16668-11

.1/50

C7,C8,C9

S16668-6

4700pF/50

T12199-1

1N4004

DISP1,DISP2,DISP3,DISP5

S17395-2

DISPLAY

J10

S20380-8

RT ANGLE HEADER

LED3

T13657-6

RED LED

R1,R2,R3,R4,R13,R14

S19400-2210

221 1/4W

R5,R6,R7

S19400-1002

10K 1/4W

R8,R9,R10

S19400-4750

475 1/4W

R11,R12

S19400-1501

1.5K 1/4W

S15128-5

+5V REG.

X3,X4

S20496-1

IC,MC14489,CMOS,DRIVER,LED,CC,MCU(SS)

S17900-8

14 PIN I.C. (SS)

DISP3

DISP2

DISPLAY
L10952-1

1.44

DISP1

10952-1
REF.

SUP’S’D’G

NO.

SHT.

STANDARD DISPLAY P.C. BD. ASSEMBLY

CHK

TYPE

4-28-2000D

C10

DISP5

J10

LED3

R11

R10

R13

R14

.49

DISP6

R12

C8
R9
R6

DISP7

Return to Master TOC

1.64

Ch’ge. Sht. No.

DISP6,DISP7

~.04

Return to Section TOC

DATE 5-20-98

S13490-25

DR R.T.

IDENTIFICATION

PART NO.

FULL

SCALE

EQUIP.

REQ’D

THE LINCOLN ELECTRIC CO.

ITEM
C1

SUBJECT

POWER MIG 255

DISPLAY PC BOARD ASSEMBLY - (L10952-1)

CLEVELAND, OHIO U.S.A.

Return to Master TOC
Return to Master TOC

G-9

ELECTRICAL DIAGRAMS

3-12-99

Return to Section TOC
Return to Section TOC

G-9

0
~.04

5.80

Return to Master TOC

.20

2.90

5.60

L 10952-1

Return to Section TOC

NOTE:

POWER MIG 255

204

208S

208

208R

400V

5W
10

204S

209S

5W
10

J1
7

C2
.68
400V

209R

Return to Master TOC

Return to Section TOC

C1
.68

Return to Master TOC

Return to Section TOC

SNUBBER PC BOARD SCHEMATIC - (S24374)

209

NOTES :

LABELS

GENERAL INFORMATION
N.A.

SINCE COMPONENTS OR CIRCUITRY ON
CIRCUIT BOARD

MAY CHANGE

THE INTERCHANGEABILITY

Return to Master TOC

THIS DIAGRAM MAY NOT

Return to Section TOC

G-10

ELECTRICAL DIAGRAMS
S 24374

Return to Section TOC

G-10

OR CIRCUITRY OF

A PRINTED
ELECTRICAL SYMBOLS PER E1537

WITHOUT AFFECTING

OF A COMPLETE

BOARD.

SHOW THE EXACT COMPONENTS

CONTROLS HAVING A COMMON

CODE NUMBER.

Ch’ge.Sht.No.

XB-RW
3-12-99

CAPACITORS =

MFD ( .022/50V

RESISTORS = Ohms (
DIODES =

1A, 400V

1/4W

SUPPLY

POWER SUPPLY SOURCE POINT

UNLESS OTHERWISE SPECIFIED)

EARTH GROUND CONNECTION

(UNLESS OTHERWISE SPECIFIED)

COMMON CONNECTION

EQUIP.

THE LINCOLN ELECTRIC CO.

TYPE

CLEVELAND, OHIO U.S.A.
SCALE
DR.

NOTE:

FRAME CONNECTION

VOLTAGE NET

UNLESS OTHERWISE SPECIFIED)

MAB

DATE

SUBJECT

POWERMIG 255
SNUBBER BOARD

NONE

5-12-98

CHK.

SUP’S’D’G.

SHT.
NO.

S 24374

POWER MIG 255

Return to Master TOC

G-11

ELECTRICAL DIAGRAMS

SNUBBER PC BOARD ASSEMBLY - (M19248-1)

M 19248-1

Return to Section TOC

G-11

.20

4.00

REQ’D

ITEM

1.80

IDENTIFICATION

PART NO.

C1,C2

T11577-68

S18248-8

0.68 MFD /400 WVDC CAPACITOR
HEADER

R1,R2

T14648-25

10 5W

~.04

3.80
SNUBBER

Return to Master TOC

CAPACITORS = MFD/VOLTS

Return to Master TOC

Return to Section TOC

M19248-1

.20
Return to Master TOC

Return to Section TOC

0
0

2.00

~.04
Ch’ge. Sht. No.
XB
3-12-99

THE LINCOLN ELECTRIC CO.

SUBJECT
SCALE

NOTE:

SP WELDERS

TYPE

CLEVELAND, OHIO U.S.A.

1-12-2001D

EQUIP.

DR R.T.

SNUBBER P.C. BOARD AS’BLY

FULL

DATE 5-13-98

SHT.
CHK

REF. M16647-1

SUP’S’D’G

NO.

M 19248-1
POWER MIG 255

We need to know if there are errors in our manuals. We also value any suggestions as to
additional tests or procedures that would make this SVM a better tool for you.
If you discover new or different “Problems or Symptoms” that are not covered in the three column troubleshooting chart, please share this information with us. Please include the
machine’s code number and how the problem was resolved.

Thank You,
Technical Services Group
Lincoln Electric Co.
22801 St. Clair Ave.
Cleveland, Ohio 44117-1199

Return to Master TOC

SVM ERROR REPORTING FORM

FAX 216-481-2309

SVM Number ___________________________
Page Number if necessary__________________

Return to Master TOC

Your Company__________________________
Your Name_____________________________

Please give detailed description below:
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________

SD287 04/06

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Modify Date                     : 2009:11:05 13:10:54-05:00
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Format                          : application/pdf
Creator                         : Rita Wood
Title                           : SVM144.PDF
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Page Count                      : 108

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Lincoln Electric Power Mig 255 Svm144 B Users Manual

SVM144-B to the manual 4004c637-834f-4269-b98d-a225789a81fc

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