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ORDER NO.PAPMOSH1201015CE

Microwave Oven

NN-SD452W
NN-ST462M
NN-ST452W
BPQ (U.K.)
EPG (Continental Europe)

Microwave

Oven

NN-SD452W / NN-ST462M / NN-ST452W

CONTENTS
Page
1 SCHEMATIC DIAGRAM

2 DESCRIPTION OF OPERATING SEQUENCE

Page
5.1. Primary, Secondary Latch Switch interlocks & Power
Relay RY1

2.1. Variable power cooking control

5.2. Short Switch

2.2. Inverter power supply circuit

5.3. Magnetron

2.3. Turbo defrost, Auto cook

5.4. key board membrane (Membrane switch assembly)

2.4. Sensor cooking

5.5. Inverter power supply (U)

2.5. Steam sensor and digital programmer circuit

5.6. Temperature thermistor

3 CAUTIONS TO BE OBSERVED WHEN TROUBLESHOOTING 8
3.1. Check the grounding

3.2. Inverter warnings

3.3. Part replacement.

6 MEASUREMENTS AND ADJUSTMENTS

6.1. Adjustment of primary latch switch, secondary latch switch
and short switch.
6.2. Measurement of microwave output

3.4. When the 10A fuse is blown due to the malfunction of the

7 TROUBLESHOOTING GUIDE

short switch:

17
17
17
18

7.1. (Troubleshooting) Oven stops operation during cooking 18
7.2. (Troubleshooting) Other problems

7.3. Troubleshooting of inverter circuit (U) and magnetron

3.6. Verification after repair

7.4. Simple way of H.V. Inverter/magnetron troubleshooting 21

3.7. Sharp edges

7.5. How to check the semiconductors using an OHM meter 21

3.5. Avoid inserting nails, wire etc. through any holes in the
unit during operation.

4 DISASSEMBLY AND PARTS REPLACEMENT PROCEDURE 10
4.1. Magnetron

4.2. Digital programmer circuit (D.P.C)

7.6. H.V. INVERTER MAIN PARTS LIST (Z606YBA00QP)
8 EXPLODED VIEW AND PARTS LIST

22
23

8.1. EXPLODED VIEW

8.2. PARTS LIST

8.3. ESCUTCHEON BASE ASSEMBLY

4.4. Fan motor

8.4. DOOR ASSEMBLY

4.5. Door assembly

8.5. WIRING MATERIALS

4.6. Turntable motor

8.6. PACKING AND ACCESSORIES

4.7. Steam sensor

4.8. Inverter power supply

9.1. SCHEMATIC DIAGRAM (NN-SD452W)

9.2. SCHEMATIC DIAGRAM (NN-ST462M, ST452W)

4.3. Low voltage transformer and/or power relays (RY1, RY2)

5 COMPONENT TEST PROCEDURE

9 DIGITAL PROGRAMMER CIRCUIT

NN-SD452W / NN-ST462M / NN-ST452W

1 SCHEMATIC DIAGRAM

NN-SD452W / NN-ST462M / NN-ST452W

2 DESCRIPTION OF OPERATING SEQUENCE
2.1.

Variable power cooking
control

2.4.

Auto sensor cooking without setting a power level or selecting
a time. All that is necessary is to select an Auto Sensor
Program before starting to cook.

High Voltage Inverter Power Supply (U) controls output power
by the signal from Digital Programmer Circuit (DPC). Power
relay always stay on, but PWM (Pulse Width Modulation) signal
controls microwave output power.

Understanding Auto Sensor Cooking
As the food cooks, a certain amount of steam is produced.
If the food is covered, this steam builds up and eventually
escapes from the container. In Auto Sensor Cooking, a
carefully designed instrument, called the steam sensor
element, senses this escape of steam. Then, based upon
the Auto Sensor Program selected, the unit will
automatically determine the correct power level and the
proper length of time it will take to cook the food.

NOTE:
The ON/OFF time ratio does not correspond with the
percentage of microwave power since approximately 2
seconds are required for heating of magnetron
filament.
Variable Power Cooking
POWER SETTING
OUTPUT
MANUAL MICROWAVE
POWER(%)
DUTY
APPROX.
BPQ
EPG
ON(SEC)
OFF(SEC)
TURBO
1000W
100%
22
0
HIGH
—
90%
22
0
DEFROST
270W
25%
15
7
MEDIUM
600W
60%
22
0
LOW
440W
45%
22
0
SIMMER
300W
30%
22
0
WARM
100W
10%
8
14

2.2.

NOTE:
Auto Sensor Cooking is successful with the foods and
recipes found in the Auto Sensor Cooking Guide.
Because of the vast differences in food composition,
items not mentioned in the Cooking Guide should be
prepared in the microwave oven using power select
and time features. Please consult Variable Power
Microwave Cookbook for procedures.

Inverter power supply circuit

The Inverter Power Supply circuit powered from the line
voltage, 230V 50Hz AC input supplies 4,000V DC to the
magnetron tube, and functions in place of the H.V. transformer,
the H.V. capacitor and H.V. diode.
1. The AC input voltage 230V 50Hz is rectified to DC voltage
immediately.
2. DC voltage will be supplied to the switching devices called
IGBT. These devices are switched ON-OFF by the 20 to 40
kHz PWM (pulse width modulation) signal from the
microcomputer in the DPC.
3. This drives the High voltage transformer to increase voltage
up to 2,000V AC.
4. Then the half-wave doubler voltage rectifier circuit,
consisting of the H.V. diodes and capacitors, generates the
necessary 4,000V DC needed for the magnetron.
5. Output power of the magnetron tube is always monitored by
the signal output from the current transformer built into the
inverter circuit.
6. This signal is fed back to the microcomputer in the DPC to
determine operating conditions and output necessary to
control PWM signal to the Inverter Power Supply for control
of the output power.

2.3.

Sensor cooking

Turbo defrost, Auto cook

When the Auto Control feature is selected and the Start pad is
tapped:
1. The digital programer circuit determines the power level and
cooking time to complete cooking and indicates the
operating state in the display window.
2. When cooking time in the display window has elapsed, the
oven turns off automatically by a control signal from the
digital programmer circuit.

NN-SD452W / NN-ST462M / NN-ST452W

Explanation of the Auto Sensor Cooking process
1. During the first 10 second period there is no microwave
activity. When calculating the T2 time by using the
formula below make sure this 10 seconds is subtracted
from the T1 time. In other words, T1 time starts at the
end of the 10 second period.
2. T1 time The total amount of time it takes the microwave
oven to switch to T2 time after the 10second period.
3. T2 time When the steam escapes from the cooking
container placed in the oven, the steam sensor detects
it and the microprocessor calculates the balance of
cooking time. This T2 time is then shown in the display
and begins counting down.
Balance of cooking time (T2 time)
The balance of cooking time which is called T2 time,
can be calculated by the following formula.
T2 time (in sec.) = T1 time X K factor
NOTE:
Remember, the T1 time starts after the 10 second
period. The coefficient K is programmed into the
microprocessor memory and they are listed in the
following tables along with the P1 and P2 powers.
NOTE:
When "More" or "Less" pad is selected, the K factor
varies resulting in T2 time to be increased or decreased.
Example of calculating the T2 time
Example 1: If the T1 time is measured to be 2 minutes and
40 seconds after the 10 second period.
T2 = T1 × K
= 2 min. and 40 sec. × 0.1
= 160sec. × 0.1
= 16 sec.
Category
BPQ
EPG

2.5.

Fresh
Vegetable

P1
Power
900W
1000W

P2
Power
900W
1000W

K Factor
Standard
0.5
0.5

Steam sensor and digital
programmer circuit

In order to determine if the steam sensor function of the digital
programmer circuit is working, do the following test.
1. Place a water load (150 cc) in the oven.
2. Tap Sensor Reheat pad.
3. Tap Start pad.
4. Steam Sensor detects steam about 1.5 to 4 minutes after
the Start pad is tapped.
5. T1 time cooking automatically switches to remaining time
for cooking (T2).
6. The remaining cooking time (T2) appears in display
window. If the following cooking time appears, Steam
Sensor function is normal.
T1 TIME
50 Sec. ~ 12 Min.

T2 TIME (Remainingcooking time)
0 Sec. ~ 10 Min.42 Sec.

NN-SD452W / NN-ST462M / NN-ST452W

3 CAUTIONS TO BE OBSERVED WHEN
TROUBLESHOOTING
Unlike many other appliances, the microwave oven is a high
voltage, high current device. It is free from danger in ordinary
use, though extreme care should be taken during repair.
CAUTION
Servicemen should remove their watches & rings whenever
working close to or replacing the magnetron.

3.1.

Check the grounding

Do not operate on a two wire extension cord. The microwave
oven is designed to be grounded when used. It is imperative,
therefore, to ensure the appliance is properly grounded before
beginning repair work.

3.2.

Inverter warnings

WARNING HIGH VOLTAGE AND HIGHTEMPERATURE
(HOT/LIVE) OF THE INVERTERPOWER SUPPLY (U)
The High Voltage Inverter Power Supply generates very
high voltage and current for the magnetron tube. Though it
is free from danger in ordinary use, extreme care should be
taken during repair.

Grounding of the inverter circuit board
WARNING
CAPACITORS

DISCHARGE

THE

HIGH

VOLATGE

For about 30 seconds after the oven is turned off, an
electric charge remains in the high voltage capacitors of the
Inverter Power Supply circuit board.

The aluminum heat sink is also energized with high voltage
(HOT), do not touch when the AC input terminals are
energized. The power device Collector is directly connected
to the aluminum heat sink.

When replacing or checking parts, remove the power plug
from the outlet and short the inverter output terminal of the
magnetron filament terminals to the chassis ground with an
insulated handle screwdriver to discharge. Please be sure
to contact the chassis ground side first and then short to the
output terminal.

The aluminum heat sink may be HOT due to heat energy,
therefore, extreme care should be taken during servicing.

H.V. Inverter warning
WARNING FOR INVERTER POWER SUPPLY (U)
GROUNDING
Check the High Voltage Inverter Power Supply circuit
grounding. The high voltage inverter power supply circuit
board must have a proper chassis ground. The inverter
grounding plate must be connected to the chassis. If the
inverter board is not grounded it will expose the user to very
high voltages and cause extreme DANGER! Be sure that
the inverter circuit is properly grounded via the inverter
grounding plate.

NN-SD452W / NN-ST462M / NN-ST452W

3.6.

Discharging the high voltage capacitors
WARNING

1. After repair or replacement of parts, make sure that the
screws of the oven, etc. are neither loosen or missing.
Microwave energy might leak if screws are not properly
tightened.

There is high voltage present with high current capabilities
in the circuits of the primary and secondary windings, choke
coil and heat sink of the inverter. It is extremely dangerous
to work on or near these circuits with the oven energized.
DO NOT measure the voltage in the high voltage circuit
including the filament voltage of the magnetron.

2. Make sure that all electrical connections are tight before
inserting the plug into the wall outlet.
3. Check for microwave energy leakage.

WARNING

CAUTION OF MICROWAVE RADIATION LEAKAGE

Never touch any circuit wiring with your hand or with an
insulated tool during operation.

3.3.

USE CAUTION NOT TO BECOME EXPOSED TO
RADIATION FROM THE MICROWAVE MAGNETRON OR
OTHER PARTS CONDUCTING MICROWAVE ENERGY.

Part replacement.

IMPORTANT NOTICE

When troubleshooting any part or component is to be replaced,
always ensure that the power cord is unplugged from the wall
outlet.

3.4.

1. The following components have potentials above 2000V
while the appliance is operated.
• Magnetron

When the 10A fuse is blown
due to the malfunction of the
short switch:

• High voltage transformer (Located on inverter (U))
• High voltage diodes (Located on inverter (U))
• High voltage capacitors (Located on inverter (U))
Pay special attention to these areas.

WARNING

2. When the appliance is operated with the door hinges or
magnetron installed incorrectly, the microwave leakage
can exceed more than 5mW/cm 2. After repair or
exchange, it is very important to check if the magnetron
and the door hinges are correctly installed.

When the 10A 250V fuse is blown due to the malfunction of
the short switch, replace all of the components (primary
latch switch, short switch and power relay RY1).
1. This is mandatory. Refer to “measurements and
adjustments” for the location of these switches.

3.7.

2. When replacing the fuse, confirm that it has the
appropriate rating for these models.

Sharp edges

CAUTION

3. When replacing faulty switches, be sure the mounting
tabs are not bent, broken or deficient in their ability to
hold the switches.

3.5.

Verification after repair

Please use caution when disassembling or reassembling
internal parts. Some exposed edges may be sharp to the
touch and can cause injury if not handled with care.

Avoid inserting nails, wire etc.
through any holes in the unit
during operation.

Never insert a wire, nail or any other metal object through the
lamp holes on the cavity or any holes or gaps, because such
objects may work as an antenna and cause microwave
leakage.

NN-SD452W / NN-ST462M / NN-ST452W

4 DISASSEMBLY AND PARTS REPLACEMENT
PROCEDURE
4.1.

Magnetron

1. Discharge the high voltage capacitor.
2. Remove 1 screw holding air guide A on the magnetron.
3. Remove 1 screw holding air guide A on cavity top plate.
4. Remove 1 screws holding thermistor on the magnetron.

NOTE:
After replacement of the magnetron, tighten mounting
screws properly, making sure there is no gap between
the waveguide and the magnetron to prevent
microwave leakage.
CAUTION
When replacing the magnetron, be sure the antenna gasket is in
place.

5. Remove 1 screw holding air guide A on the wave guide,
then remove the air guide A.

4.2.

Digital programmer circuit
(D.P.C)

CAUTION:
Be sure to ground any static electric charge built up in
your body before handling the DPC.
1. Disconnect connector CN701 on H.V. Inverter board.
2. Remove 1 screw holding escutcheon base and slide the
escutcheon base upward slightly.
3. Remove all screws holding D.P.C. board on escutcheon
base.
4. Separate D.P.C board from tabs on the escutcheon base
and remove D.P.C board.
To replace membrane key board
5. Use tools such as kinfe etc. to lift the edge of escutcheon
sheet and peel off escutcheon sheet & key board
membrane completely from escutcheon base.

6. Remove 4 screws holding the magnetron.

NOTE:
1. The membrane key board is attached to the
escutcheon base with double faced adhesive tape.
Therefore, applying hot air such as using a hair
dryer is recommended for smoother removal.
2. When installing the new key board membrane, make
sure that the surface of escutcheon base is clean to
prevent a malfunction or shorted contacts.

NN-SD452W / NN-ST462M / NN-ST452W

4.5.

Door assembly

1. Support the door, remove 3 screws holding hinge A.

4.3.

Low voltage transformer
and/or power relays (RY1,
RY2)

CAUTION:

2. Open the door, remove door(U) and hinge A from cavity.

Be sure to ground any static electric charge built up in
your body before handling the DPC.

NOTE:
Support the door before opening.

1. Replace D.P.C. board.
(A) Using solder wick or a desoldering tool and 30W
soldering iron carefully remove all solder from the terminal
pins of the low voltage transformer and/or power relays.
CAUTION:
Do not use a soldering iron or desoldering tool of
more than 30 watts on D.P.C. contacts.
(B) With all the terminal pins cleaned and separated from
D.P.C. contacts, remove the defective transformer/power
relays, Replace components making sure all terminal pins
are inserted completely resolder all terminal contacts
carefully.

4.4.

Fan motor

1. Disconnect 2 lead wires from fan motor terminals.
2. Remove 2 screws at location on oven attaching orifice
assembly.
3. Remove orifice assembly from oven assembly.

3. Remove door C from door A (U) & door E by carefully
pulling outward starting from upper right hand corner using
a flat blade screwdriver.

4. Remove fan blade from the fan motor shaft by pulling it
straight out.

4. Separate door E from tabs on door A (U) and remove door
A (U).

5. Remove 2 screws holding fan motor to orifice.

5. Remove door key and door key spring from door E.

NN-SD452W / NN-ST462M / NN-ST452W

9. Tighten 2 mounting screws.

6. Replace other components.
To re-install components:
NOTE:
After replacement of the defective component parts
of the door, reassemble it properly and adjustment
so as to prevent an excessive microwave leakage.
Adjustment of the door assembly (Refer page 17).
7. Place the hole of hinge A into the door’s upper hinge pin.

Be sure the gap between door E and cavity front plate will
be 0.3~0.7mm.
NOTE:
Always perform the microwave leakage measurement
test after installation and adjustment of door assembly.

8. Use your left index finger to support the door’s lower hinge
pin while guiding the door’s hinge A into the cavity slot.
Then lower your finger to seat the door onto the hinge.

NOTE:
Door alignment is crucial. If door is misaligned,
apply pressure until alignment is achieved.
NOTE:
Adjust so that the upper portion of the door will
touch firmly to the oven cavity front plate, without
pushing the door. If the door assembly is not
mounted properly, microwave power may leak from
the clearance between the door and oven.

NN-SD452W / NN-ST462M / NN-ST452W

4.6.

Turntable motor

4.7.

1. Remove the motor cover by breaking off at the 8 spots
indicated by arrows with a cutter or the like.

Steam sensor

1. Disconnect connector CN2 from digital programmer circuit
board.
2. Disengage catch hooks on sensor cover C from orifice.

NOTE:
After removing the motor cover, be sure that cut
portions are properly trimmed or bent to the inside
so that no sharp edges will be exposed to outside.

3. Remove steam sensor from orifice.

2. Disconnect 2 lead wires connected to the turntable motor.

NOTE:

3. Remove the turntable motor by removing screw.

When installing the steam sensor, make sure that
the direction of steam sensor is as shown in figure.

NOTE:
After reinstalling the new turntable motor and
reconnecting the 2 lead wires, reinstall the motor
cover by rotating it around 180, tucking the 2 tabs
under the base in the 2 provided slots, then screw
the single tab to the base using a 4mm × 6mm
screw.

NN-SD452W / NN-ST462M / NN-ST452W

4.8.

Inverter power supply

6. Remove 1 screw holding H.V.Inverter to Inverter bracket.

CAUTIONS
1. Always leave the grounding plate in place.
2. Always securely tighten the ground screw through the bottom of the
chassis (base).
3. Securely connect 3 lead wire connectors.
4. Make sure the heat sink has enough space (gap) from the oven.
Take special care not to dress any lead wire over the aluminum heat
sink because it is hot.

1. Discharge high voltage charge.
2. Remove the H.V.lead wire from magnetron terminals.
3. Disconnect 2 connectors from CN701 & CN702 on
H.V.Inverter(U).
4. Remove 1 screw holding grounding plate to the base.

7. Remove 1 screw holding grounding plate to H.V. Inverter.

5. Press 1 encircled locking tab and then slide 4 locking tabs
of Inverter bracket at the bottom of the base in direction of
arrows.
8. Seperate H.V. Inverter from Inverter bracket by freeing 3
catch hooks on the Inverter bracket.

NN-SD452W / NN-ST462M / NN-ST452W

5 COMPONENT TEST PROCEDURE
5.3.

WARNING
1. High voltage is present at the output terminals of the High Voltage
Inverter (U) including aluminum heat sink during any cook cycle.
2. It is neither necessary nor advisable to attempt measurement of the
high voltage.
3. Before touching any oven components, or wiring, always unplug
the power cord and discharge the high voltage capacitors (see page
8).

5.1.

Magnetron

Continuity checks can only indicate an open filament or a
shorted magnetron. To diagnose for an open filament or
shorted magnetron.
1. Isolate magnetron from the circuit by disconnecting the
leads.
2. A continuity check across magnetron filament terminals
should indicate one ohm or less.

Primary, Secondary Latch
Switch interlocks & Power
Relay RY1

3. A continuity check between each filament terminal and
magnetron case should read open.

1. Unplug lead connectors to Power Relay RY1 and verify
open circuit of the Power Relay RY1 1-2 terminals.
2. Unplug lead connectors to Primary Latch Switch and
Secondary Latch Switch.
3. Test the continuity of switches at door opened and closed
positions with ohm meter (low scale).
Normal continuity readings should be as follows.
Primary Latch Switch
Secondary Latch Switch
Power Relay RY1

5.2.

Door Closed
0Ω (Close)
0Ω (Close)
Ω (Open)

Door Opened
Ω(Open)
Ω(Open)
Ω(Open)

Short Switch

1. Unplug lead wires from Inverter Power Supply (U) primary
terminals.

5.4.

2. Connect test probes of ohm meter to the disconnected
leads that were connected to Inverter Power Supply (U).
3. Test the continuity of short switch with door opened and
closed positions using lowest scale of the ohm meter.

Check continuity between switch terminals, by tapping an
appropriate pad on the key board. The contacts assignment of
the respective pads on the key board is as shown in digital
programmer circuit.

Normal continuity readings should be as follows.
Door Opened
0Ω (Close)

key board membrane
(Membrane switch assembly)

Door Closed
Ω (Open)

NN-SD452W / NN-ST462M / NN-ST452W

5.5.

Inverter power supply (U)

3. Plug in the oven’s AC power supply cord into outlet.
4. Program DPC.

DO NOT try to REPAIR H.V. Inverter power supply
(U).Replace complete H.V. Inverter(U) Unit.

For SD452W model
a. Press Clock button once.
b. Press Timer button once.
c. Press Start button once.
d. Press 1000W/600W

button once.

For ST462M & ST452W models
a. Press Timer pad twice.
b. Press Start pad once.
c. Press Micro Power pad once.
5. Program oven at High power for 1 minute and press [Start]
pad.
a. After approximately 3 seconds, oven stops operating.
b. During oven operation,
approximately 0.4A.
Unplug CN701

the

INPUT CURRENT
0.4A

input

current

FAILURE CODE
Oven stops in 3
seconds after started.

WARNING: HIGH VOLTAGE

If both a and b check OK, the Inverter Power Supply (U) can be
determined to be OK.

Test if failure codes H95, H97 or H98 appear when performing
the following procedure. It is recommended to use an AC line
input current ammeter for testing.

5.6.

The thermistor that is attached to the magnetron detects the
temperature of the magnetron and will stop magnetron
operation when overheating is detected. A normal thermistor´s
resistance is 35KΩ to 110KΩ for an ambient temperature range
of 10-30 degree C.

Test 1
1. With the oven unit’s AC power supply cord is unplugged
from the wall outlet, unplug the 2 pin H.V. connector CN703
from the magnetron tube.
2. Place 1 liter of water load into oven cavity.

If the resistance reading is out of the range stated here, the
thermistor is detective and must be replaced.

3. Plug in the oven’s AC power supply cord into outlet.

It is also possible to display thermistor level by taking the
following steps.

4. Program DPC.
For SD452W model

For SD452W model

a. Press Clock button once.

1. Program the DPC into TEST MODE (Plug-in oven → press
Clock button once → press Timer button once → press
Start button once → press 1000W/600W button once).

b. Press Timer button once.
c. Press Start button once.
d. Press 1000W/600W

button once.

2. Program oven at Standing Time for 1 minute and press
[Start] button.

For ST462M & ST452W models
a. Press Timer pad twice.

3. Press Sensor Reheat once, the thermistor level reading
will shown on the display.

b. Press Start pad once.

The normal reading should be in the range of 16-230.

c. Press Micro Power pad once.

For ST462M & ST452W models

5. Program oven at High power for 1 minute and press [Start]
pad.

1. Program the DPC into TEST MODE (Plug-in oven → press
Timer pad twice → press Start pad once → press
Micro Power pad once).

a. After approximately 23 seconds, oven stops operating.
b. During oven operation, the input current is
approximately 0.5 to 1A. If both a and b are OK,
proceed to test 2.
Unplug CN703

Temperature thermistor

INPUT CURRENT
0.5 to 1A

2. Program oven at Standing Time for 1 minute and press
[Start] pad.
3. Press Reheat twice, the thermistor level reading will
shown on the display.

FAILURE CODE
Oven stops in 23
seconds after started.

The normal reading should be in the range of 16-230.

Test 2
Continued from Test 1
1. Unplug the oven’s AC power supply cord from outlet.
2. Unplug 3 pin connector CN701. CN703 remains unplugged.

NN-SD452W / NN-ST462M / NN-ST452W

6 MEASUREMENTS AND ADJUSTMENTS
6.1.

Adjustment of primary latch
switch, secondary latch switch
and short switch.

6.2.

Measurement of microwave
output

The output power of the magnetron can be determined by
performing IEC standard test procedures. However,due to the
complexity of IEC test procedures, it is recommended to test
the magnetron using the simple method outlined below.

1. Mount the Primary latch switch, the Secondary latch switch
and the Short switch to the door hook assembly as shown
in illustration.

Necessary Equipment:

NOTE:

• 1 liter beaker

No
specific
individual
adjustments
during
installation of the Primary latch switch, Secondary
latch switch or Short switch to the door hook are
required.

• Glass thermometer
• Wrist watch or stopwatch
NOTE:

2. When mounting the door hook assembly to the oven
assembly, adjust the door hook assembly by moving it in
the direction of the arrows in the illustration so that the oven
door will not have any play in it. Check for play in the door
by pulling the door assembly. Make sure that the latch keys
move smoothly after adjustment is completed. Completely
tighten the screws holding the door hook assembly to the
oven assembly.

Check the line voltage under load. Low voltage will
lower the magnetron output. Take the temperature
readings and heating time as accurately as possible.
1. Fill the beaker with exactly one liter of tap water.Stir the
water using the thermometer and record the water’s
temperature. (recorded as T1).
2. Place the beaker on the center of glass tray.
Set the oven for High power and heat it for exactly one
minute.

3. Reconnect the short switch and check the continuity of the
monitor circuit and all latch switches again by following the
component test procedures.

3. Stir the water again and read the temperature of the water.
(recorded as T2).
4. The normal temperature rise at High power level for each
model is as shown in table.
TABLE (1L-1min. test)
RATED OUTPUT
TEMPERATURE RISE
1000W
Min. 8.5°C

NN-SD452W / NN-ST462M / NN-ST452W

7 TROUBLESHOOTING GUIDE
DANGER: HIGH VOLTAGES
1. DO NOT RE-ADJUST PRESET CONTROL on the H.V.Inverter (U). It is very dangerous to repair or adjust without proper test equipment
because this circuit generates very large current and high voltage. Operating a misaligned inverter circuit is dangerous.
2. Ensure proper grounding before troubleshooting.
3. Be careful of the high voltage circuitry, taking necessary precautions when troubleshooting.
4. Discharge high voltage remaining in the H.V.Inverter (U).
5. When checking the continuity of the switches or the H.V.Inverter, disconnect one lead wire from these parts and then check continuity with the
AC plug removed. Doing otherwise may result in a false reading or damage to your meter. When disconnecting a plastic connector from a
terminal, you must hold the plastic connector instead of the lead wire and then disconnect it, otherwise lead wire may be damaged or the
connector cannot be removed.
6. Do not touch any parts of the circuitry on the digital programmer circuit, since static electric discharge may damage this control panel. Always
touch ground while working on this panel to discharge any static charge in your body.
7. 230-240V AC is present on the digital programmer circuit (Terminals of power relay’s and primary circuit of Digital Programmer Circuit). When
troubleshooting, be cautious of possible electrical shock hazard.

Before troubleshooting, operate the microwave oven following the correct operating procedures in the instruction manual in order
to find the exact cause of any trouble, since operator error may be mistaken for the oven’s malfunction.

7.1.

(Troubleshooting) Oven stops operation during cooking

SYMPTOM
CAUSE
CORRECTIONS
1. Oven stops in 3 seconds after No input AC is supplied to H.V.Inverter (U) 1. Latch Switch
. pressing [Start] button.
CN702 terminals
2. Power relay RY1
3. Loose lead wire connector CN701, CN702
4. H.V. Inverter (U)
Oven stops in 23 seconds after H.V.Inverter (U) operates by the control signals 1. Magnetron
pressing [Start] button.
from DPC but magnetron is not oscillating
2. Loose lead wire connector CN703
3. H.V. Inverter (U)
Oven stops in 10 seconds after Steam sensor circuit is not functioning
1. Steam sensor
pressing [Start] button.
2. DPC
(Auto sensor cooking)
3. Open or loose wiring of sensor terminal from
connector CN2 on DPC
2. No display and no operation at all. Most probably loose connection of connectors, or 1. Align door, Door Latch Switches
Fuse is blown.
door latch mechanism is not adjusted properly
2. Loose wiring connectors

NN-SD452W / NN-ST462M / NN-ST452W

7.2.

(Troubleshooting) Other problems

SYMPTOM
1. Oven is dead.
Fuse is OK.
No display and no operation at all.
2. No display and no operation at all.
Fuse is blown.

3. Oven does not accept key input
(Program)

4. Fan motor turns on when oven is
plugged in with door closed.

5. Timer starts count down but no
microwave oscillation.
(No heat while oven lamp and fan
motor turn on)

1.
2.
3.
4.
1.
2.
3.
4.

1.
2.
3.
4.
1.
2.
3.
1.
2.

6. Oven can program but timer does not
start countdown.
7. Microwave output is low. Oven takes
longer time to cook food.

8. Fan motor turns on and turntable
motor rotates when door is opened.
9. Oven does not operate and return to
plugged in mode as soon as [Start]
button is pressed.
10. Loud buzzing noise can be heard.
11. Oven stops operation during cooking.

4.
5.
6.
1.
2.
3.
1.
2.
3.
1.

CAUSE
CORRECTIONS
Open or loose lead wire harness
Open thermal cutout / thermistor
Check thermal cutout is defective.
Open low voltage transformer
Defective DPC
Shorted lead wire harness
Check adjustment of primary, secondary latch
switch and short switch including door.
Defective primary latch switch (NOTE 1)
Defective short switch (NOTE 1)
Defective Inverter Power Supply (U)
NOTE 1:
All of these switches must be replaced at the same time.
Check continuity of power relay RY1 contacts (between 1 and 2) and if it has continuity, replace
power relay RY1 also.
Key input is not in proper sequence
Refer to operation procedure.
Open or loose connection of membrane key
button to DPC (Flat cable)
Shorted or open membrane key board
Defective DPC
Refer to DPC troubleshooting.
Misadjustment or loose wiring of secondary
Adjust door and latch switches.
latch switch
Defective secondary latch switch
Door switch CN12
Off-alignment of primary latch switch
Adjust door and latch switches.
Open or loose connection of high voltage
circuit especially magnetron filament circuit
NOTE:
Large contact resistance will cause lower
magnetron filament voltage and cause
magnetron to have lower output and/or be
intermittent.
Defective high voltage component
Check high voltage component according to
H.V. Inverter Power Supply (U)
component test procedure and replace if it is
Magnetron
defective.
Open or loose wiring of power relay RY1
Defective primary latch switch
Defective DPC or power relay RY1
Refer to DPC troubleshooting
Open or loose wiring of secondary latch switch
Off-alignment of secondary latch switch
Defective secondary latch switch
Decrease in power source voltage
Consult electrician
Open or loose wiring of magnetron filament
circuit.(Intermittent oscillation)
Aging change of magnetron
Low voltage transformer on DPC.

1. Defective DPC

Check grounding connector on escutcheon
base.

1. Loose fan and fan motor
1. Open or loose wiring of primary and
secondary latch switch
2. Operation of thermal cutout

Adjust door and latch switches.

NN-SD452W / NN-ST462M / NN-ST452W

7.3.

Troubleshooting of inverter circuit (U) and magnetron

This oven is programmed with a self diagnostics failure code system which will help for troubleshooting. H95, H97, H98 and H99
are the provided failure codes to indicate magnetron and inverter circuit problem areas. This section explains failure codes of H95,
H97, H98 and H99. First, you must program the DPC into TEST MODE, For SD452W model: press Clock button once → press
Timer button once → press Start button once → press 1000W/600W button once, For ST462M & ST452W model: press
Timer pad twice → press Start pad once → press Micro Power pad once. Program unit for operation. H95, H97, H98, H99
appears in display window a short time after [Start] pad is pressed and there is no microwave oscillation.

Alternate way to troubleshoot oven with AC Ampere meter used
H95, H97, H98, H99 appears in display window a short time after [Start] button is pressed and no microwave oscillation with AC
Ampere meter used for troubleshooting.

NN-SD452W / NN-ST462M / NN-ST452W

7.4.

Simple way of H.V. Inverter/magnetron troubleshooting

Purpose:
Simple way (3/23 seconds rule) of identifying whether it’s Magnetron, Inverter, or others.
Set-up:
The unit under question is connected through the Ammeter as shown below.

Procedure:
Follow the matrix table below to identify the problem source.
Note:
Do not replace both Inverter board and Magnetron simultaneously and automatically without going through this
procedure.
Power will:
Ammeter reading is:
Shut off in 23 seconds 1. Between 0.5A and 1.0A.
after “Start”.
2. Between 1.0A and 2.0A.

To do:
Remedy:
Check and repair open magnetron circuit Open magnetron wiring between Inverter
and magnetron terminal.
Check continuity of D702 in Inverter PCB.

1. D702 shorted

Shut off in 3 seconds 1. Less than 0.5A
after “Start”

7.5.

Replace H.V.Inverter
(Z606YBA00QP)
2. D702 is OK
Replace magnetron
Check open circuit: Latch Switch, DPC, Replace defective component(s), or
Power Relay and CN701
correct switch, cables and connectors.

How to check the semiconductors using an OHM meter

NN-SD452W / NN-ST462M / NN-ST452W

7.6.

H.V. INVERTER MAIN PARTS LIST (Z606YBA00QP)

Ref. No.
Q701
C701
C702
DB701
L701
R702
T701
D701,D702
C706
C707

Part No.
Z1JAEV000003
ZCWHC3B104JA
ZCWF4305N851
Z0FBBQ000006
Z5020W100AP
Z0CM562JA002
Z609ABA00GP
Z0FBAZ000003
Z0C3F562A002
Z0C3F822A002

Part Name & Description
IGBT
FILM CAPACITOR
FILM CAPACITOR
RECTIFIER BRIDGE
CHOKE COIL
SAND BAR RESISTOR
TRANSFORMER
DIODE
FILM CAPACITOR
FILM CAPACITOR

Pcs/Set
1
1
1
1
1
1
1
2
1
1

Remarks
0.1µF,1000VDC
3µF,250VDC

(INCLUDING D701,D702,C706,C707)
5600PF/3KV
8200PF/3KV

NN-SD452W / NN-ST462M / NN-ST452W

8 EXPLODED VIEW AND PARTS LIST
8.1.

EXPLODED VIEW

NN-SD452W / NN-ST462M / NN-ST452W

8.2.

PARTS LIST

NOTE:
1. When ordering replacement part(s), please use part number(s) shown in this part list.
Do not use description of the part.
2. Important safety notice:
Components identified by

mark have special characteristics important for safety.

When replacing any of these components, use only manufacture’s specified parts.
Ref. No.
1
1
2
4
5

Part No.
Z00064080BP
Z00069000EP
Z21559Y10QP
Z10019Y00AP
Z10089W40HPS

Part Name & Description
CAUTION LABEL
CAUTION LABEL
OVEN STICKY PAPER
BASE
RUBBER FOOT

Pcs/Set
1
BPQ
1
EPG
1
1
2

6
6
7
8
9

Z10099Y00SAP
Z10099Y00HAP
Z200A9Y00SQP
Z20559Y00AP
Z21319Y00AP

CABINET BODY (U)
CABINET BODY (U)
OVEN (U)
COVER
PULLY SHAFT

1
1
1
1
1

11
12
13

Z290D6W50XP
Z30209X70EP
Z11619Y00AP

ROLLER RING (U)
DOOR HOOK
REINFORCEMENT BRACKET

1
1
1

17
18
19
20

Z400A9Y00QP
Z40089Y00AP
Z40259Y00AP
Z41449Y10QP

FAN MOTOR
FAN BLADE
AIR GUIDE A
ORIFICE

1
1
1
1

21
22
24
25

Z607S4T00AP
Z64499Y00AP
Z64508660AP
Z65439Y00AP

STEAM SENSOR
SENSOR COVER A
SENSOR COVER B
SENSOR COVER C

1
1
1
1

26
27
28
29
30

Z61425U30XN
Z61415U30XN
Z61459V00XP
Z612E9C30BP
Z61785U30XN

MICRO SWITCH
MICRO SWITCH
THERMAL CUTOUT
INCANDESCENT LAMP (U)
MICRO SWITCH

1
1
1
1
1

31
32
33
35

Z606YBA00QP
Z2M261-M39R
Z62309W40HP
Z66629Y00AP

H.V.INVERTER (U)
MAGNETRON
FUSE
GROUNDING PLATE

1
1
1
1

36
37
37
38
40

Z63266S30XP
Z900C9Y10KT
Z900C9Y10PT
Z607X9Y60BP
Z30069Y00AP

TURNTABLE MOTOR
AC CORD W/PLUG
AC CORD W/PLUG
NOISE FILTER
HINGE A

1
1
1
1
1

41
43
44
45

ZTWFL4+12T
ZTWFA4+12D
ZTWFA4+12LR
Z65859Y00AP

SCREW
SCREW
SCREW
INVERTER BRACKET

4
4
3
1

55
56
57

Z31389X70EP
Z31369X70EP
Z31379X70EP

HOOK LEVER C
HOOK LEVER A
HOOK LEVER B

1
1
1

Remarks

ST462M
SD452W,ST452W

(PRIMARY LATCH SWITCH)
(SECONDARY LATCH SWITCH)

(SHORT SWITCH)

(10A)

BPQ
EPG

FOR MAGNETRON
FOR CABINET BODY
FOR HINGE A

NN-SD452W / NN-ST462M / NN-ST452W

8.3.
8.3.1.

ESCUTCHEON BASE ASSEMBLY
NN-SD452W

Ref. No.
E1
E2
E3
E4
E5

Part No.
Z603L9Y70EP
Z603Y9Y70EP
Z80349Y70HEP
Z891P9Y00HAP
Z83379Y70HEP

Part Name & Description
D.P.CIRCUIT (AU)
D.P.CIRCUIT (DU)
ESCUTCHEON BASE
DOOR OPENING BUTTON (U)
MEMBRANE SHEET

Pcs/Set
1
1
1
1
1

E6
E7
E8
E9
E10

Z82569Y00AP
Z80375K00AP
Z803G9M60HBP
Z80189Y40AP
Z82989Y40HAP

DOOR OPENING LEVER
COOK BUTTON SPRING
POP-OUT DIAL (U)
DIAL SUPPORT
BUTTON

1
1
1
1
1

SD452W EPG
SD452W EPG
SD452W EPG

E11
E13
E14
E15

Z82989Y90HAP
Z66167D00AP
Z81279Y40AP
Z00079Y70HEP

BUTTON B
FLAT CABLE
BACK PANEL
NAME PLATE

1
1
1
1

SD452W
SD452W
SD452W
SD452W

E16

Z81269Y70BEP

DISPLAY WINDOW

SD452W EPG

Remarks
SD452W
SD452W
SD452W
SD452W
SD452W

EPG
EPG
EPG
EPG
EPG

EPG
EPG
EPG
EPG

NN-SD452W / NN-ST462M / NN-ST452W

8.3.2.

NN-ST462M, ST452W

Ref. No.
E21
E23
E23
E24
E24
E25
E25

Part No.
Z603L9Y60BP
Z80349Y10SHP
Z80349Y10HAP
Z891P9Y60SBP
Z891P9Y00HAP
Z630Y9Y60SBP
Z630Y9Y60HBP

Part Name & Description
D.P.CIRCUIT (AU)
ESCUTCHEON BASE
ESCUTCHEON BASE
DOOR OPENING BUTTON (U)
DOOR OPENING BUTTON (U)
MEMBRANE SWITCH (U)
MEMBRANE SWITCH (U)

Pcs/Set
1
1
1
1
1
1
1

E26
E27
E28
E29

Z82569Y00AP
Z80375K00AP
Z81279Y00AP
Z66139Y20AP

DOOR OPENING LEVER
COOK BUTTON SPRING
BACK PANEL
BACKSTOP

1
1
1
1

ST462M BPQ,ST452W BPQ
ST462M BPQ,ST452W BPQ

E35
E35

Z00079Y60SBP
Z00079Y60HBP

NAME PLATE
NAME PLATE

1
1

ST462M BPQ
ST452W BPQ

Remarks
ST462M
ST462M
ST452W
ST462M
ST452W
ST462M
ST452W

BPQ,ST452W BPQ
BPQ
BPQ
BPQ
BPQ
BPQ
BPQ

NN-SD452W / NN-ST462M / NN-ST452W

8.4.

DOOR ASSEMBLY

Ref. No.
D1
D2
D2
D2
D3
D4
D5

Part No.
Z30189Y00AP
Z302A9Y70HEP
Z302A9Y60SBP
Z302A9Y60HBP
Z302K9Y00AP
Z30215G10XN
Z30859Y00AP

Part Name & Description
DOOR KEY A
DOOR A (U)
DOOR A (U)
DOOR A (U)
DOOR E (U)
DOOR KEY SPRING
DOOR C

Z31459Y00AP

DOOR SCREEN A

Pcs/Set
1
1
SD452W EPG
1
ST462M BPQ
1
ST452W BPQ
1
1
1
1

Remarks

NN-SD452W / NN-ST462M / NN-ST452W

8.5.

Ref. No.
W1
W2

WIRING MATERIALS

Part No.
Z030A9Y60BP
Z030E9Y10QP

Part Name & Description
LEAD WIRE HARNESS
H.V.LEAD WIRE

Pcs/Set
Remarks
1
(INCLUDING MAGNETRON THERMISTOR)
1

NN-SD452W / NN-ST462M / NN-ST452W

8.6.

PACKING AND ACCESSORIES

Ref. No.
P1
P1
P2
P2
P2
P3
P4
P5

Part No.
Z00039Y60BP
Z00039Y70EP
Z01029Y70HEP
Z01029Y60SBP
Z01029Y60HBP
Z01049Y00AP
Z01059Y00AP
Z01068100XN

Part Name & Description
INSTRUCTION MANUAL
INSTRUCTION MANUAL
PACKING CASE,PAPER
PACKING CASE,PAPER
PACKING CASE,PAPER
UPPER FILLER
LOWER FILLER
P.E.BAG

P6
P8
P9
P10

Z01078J00XN
Z06014N30BP
Z01099Y00AP
Z000B9Y70EP

DOOR SHEET
COOKING TRAY
SHEET
COOK BOOK

Pcs/Set
1
1
1
1
1
1
1
1
1
1
1
1

Remarks
ST462M
SD452W
SD452W
ST462M
ST452W

BPQ,ST452W BPQ
EPG
EPG
BPQ
BPQ

ST462M BPQ
EPQ

NN-SD452W / NN-ST462M / NN-ST452W

9 DIGITAL PROGRAMMER CIRCUIT
9.1.

SCHEMATIC DIAGRAM (NN-SD452W)

NN-SD452W / NN-ST462M / NN-ST452W

9.2.

SCHEMATIC DIAGRAM (NN-ST462M, ST452W)

NN-SD452W / NN-ST462M / NN-ST452W

01/12
S-9Y6, S-9Y7
Printed in China

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