NiCOM USA NA501FP05 BROADCAST AMPLIFIER User Manual users manual
NiCOM USA BROADCAST AMPLIFIER users manual
users manual
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| Date Submitted | 2005-07-28 00:00:00 |
| Date Available | 2005-07-22 00:00:00 |
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- NA 501 - 00W FMPO ER AND MAINTENANCE MANUAL CONTENTS GENERALDESCRIPTION" b) TECHNICAL FEATURES 2.1 FRONT PANEL COMZMANDS AND SIGNALLING.. 2.2 THE REAR PANEL AND THE CONNECTIONS . 2.3 TECHNICAL SPECIFICATIONS . 2.4 1/0 REMOTE CONTROL SPECIFI INSTALLATION AND USE 3.1 FOREWORDTO INSTALLATION 3.2 PLACING THE UNIT 3.3 WIRING INTO THE MAINS 3.4 ANTENNA CONNECTION 3.5 LF CONNECTION .. 3.6 OTHERRECOMME A ONS 3.7 OPERATION... 3.8 POSSIBLE MALFUNCTIONS . SERVICEANDMAINTENANCE - ..’... SERVICE MANUAL............ 6.1 SYSTEM DESCRIPTIO 6.2 INTERNALDESCRIPT IO REPAIRAND REPLACEMENT OF DAMAGED MODULES 21 DRAWINGS A.1 NA 501 amplifier front& top internal view (D1067) . NA 501 amplifier, rear and bottom internal view (D1068B) . A.2 NA 501, general electric diagram, ver. 220-240Vac (EOS93) NA 501, wiring diagrameO895) NA 501, power supply front—end (E1003) ..... . ..................................................... SRFB lKOAL2, RF control display, RF controls & measures board andcomponent layout (E0894) .............................................................................. SRFB1K5ALM, 48V/40A SMPS regulatormodule diagram and layoutpower and controlsection ......................................................................... .. NA 501, 500W RF amplifier assemblyelecn-ic diagram (E0857) .. SRFB lKOlN, 2-portRF input splitter diagram and layout (E0858) . .. SRFB l KOPB, 2-port RF output combiner & LPF diagram and layout (E0859) SRFBSOOW, 500Wamplifiermodule diagram and layout (150764) SRFBSOOW, 500W amplifiermodule - component layout ........... PAGE 2 NA 501 500W FM POWER AMPLIFIER 1 GENERAL DESCRIPTION The NA 501 isahighlyintegrated broadband solid-state Mos-Pet FM amplifier of 500Wrated power, fittedina4unit 19" rack, whichdo notrequire anyspecific calibrationto operate inthe87.5 + 108 MHzfi-equencyrange. Its compact size, high efficiency, wide mains range acceptance, low maintenance requirements and broadband construction, make this amplifier ideal inmedium power repeaters, inunattended posts, in N+l systems and as a reserve. Its sturdy, modular mechanical and electrical construction guarantees a high MTBF and an easy maintenance. The modulesareeasily identifiable and inspectable with few interconnections each with the other, through multi-pole connectors. The nominal RF output power is obtained over the full FM range with amere SW drive and is particularly stableagainsttime,temperawreandfiequencyvariationsbeingALC regulated, withafront panel adjustment. Theoutputpower maybe variedfromaminimum levelto thenominal levelandthe frequency varied overthefull PM range,withoutretouching the drivepoweror anyotheradjuslment than the ALC control. The output stage has a reverse interrnodulation figure, which is lower than standard bipolar construction, due to the all Mos-Fet design and approaches that of tube equipment. A simple metering and alarm section completes the amplifier, permitting an easy check of the functioning with few, unambiguous readings. Power readings and control are externally available on a remote I/O port, for an external controller. A suitable one may be supplied on requesttopermitfullremotecontroloftheUnitfromthe studiooranotherservicecentre. The whole assembly is designed in accordance with the _CCIR, FCC and fighter international norms and conforms to the recent, strict“ requirements for EMI susceptance and emission. This equipment complies in particular to ETSI EN300.384 and EN 300.447 Broadcast and EMI/EMC standards, EN60065 and EN60215 safety standards and FCC parts 73 & 74. PAGE 3 2 TECHNICAL FEATURES 2.1 FRONT PANEL COMMANDS AND SIGNALLING © © © © © _‘ © 33g3:ozzzai \ 1 m. © © © . © The front control panel carries the power on switch, the control meter, some alarm warning led‘s and aRF monitor connector. On the bottom side, a gn'dding on the panel permits the output of the ventilation air. At the RF monitor output, BNC type, a sample of the output power is available which is attmuatedSAdBtypicallyfirefiGdBm @500Woutput). Eveniftl'iisomputisfairlyflatvs fi'equency, itis not suggested tousethis foraccurate harmonicaanalysis. The switchable meter permits the reading of the most important operating parameters, Le. theforwardandreflected power(500Wf.s‘) andtheregulatedandunregulatedpowersupplyvohage (300Vdc f.s.). The 2 led's light only in case of failure. The meaning of these led is summarised on the following table: ~ LED 1 WANING VSWR WWMW9MW) mm MMMMMMMMW u-fxilueofthevulilalmsym Table 1: ~ warning led meaning PAGE 4 2.2 THE REAR PANEL AND THE CONNECTIONS The rear panel allocates theRF powerandthe I/Oports in additionto the mains powercord and fuse, the earthling screw and an auxiliary mains socket on some models. The power cord is not removable. If it is requiredalongercablethanthatpmvidedinthe factory (roughlyz meters lorig),a . suitable 3x 1.5 mmsqi powercordmayeasilyreplaoe theoriginal one. Thefusehasadifi‘erentrating for 115 or230Vac operation: be sure to adopt therighttype for your mains network The Antenna output is brought out on a type "N" connector, the input connector is also a "N" type. Aremote I/O port is available on aSUBD 25 poles, female connector. The exhaust air output opening must not be obstructed during operation: wide room must be provided during installation to permit a substained ventilation air flux. It is not permitted to insert the equipment inaclosedrackwithoutasuitable external airextraction system. An auxiliary IEC-320 female type mains outlet is provided, which is powered only when the amplifier is on, to supply the exciter. No fuses other than the general fuses (16A) are inserted on this line. Limit the power absorption from this outlet to low levels, i.e. lOOW/ 1A max. Setting the mains voltage for 115 or 230V operation requires to gain access to the inner of the equipment, removing the top cover. Be sure to remove the power cord from mains to avoid direct exposure to hazardous mains voltage; which are always present on the fuses and the input board, even with power on switch in the off position. PAGE 5 2.3 TECHNICAL SPECIFICATIONS @ lkW RF output if not otherwise specified - Frequency range: 87.5 + 108 MHz - RFinputpower 8W mm, 10 W max - RFoutputpower 500 W 10.5 dB - RF input/output impedance: 50 Q - RF input connector: N - RFoutputconnector: N - RF monitor connector: BNC - Harmonic and spurious emissions: < -70 dBc - RF monitor attenuation: 54 dB, typ. - Max total current handling capability on ‘ ~ ~ the auxiliary socket: 1A @ 230 Vac, lOOWmax, not fused - Mainssupplyrequirements: 115 / 230 Vac 50/60 Hz <950W (1250 VA) - Operatingtemperamremnge: 0 + +35 °C recommended, -10 + +50 °C max ~ Dimensions, not including the handles: 483 x. 177 x 535 mm (W x H x L) See drawings - Weight approx. 66Lbs (30 kg). 2.4 U0 REMOTE CONTROL SPECIFICATIONS Aremote l/O DB25 female connector, located on the rear panel, makes available 3 analog lines to permit remote control and surveillance of the equipment as detailed: Pin Line Range/use 1,3,21 ground common 9 ReflectedPower 0+5V vs. 0+550Wout Zo=10kn (4 V typ. @ 500W) 10 Forward Power 0+5V vs. 0+550Wout Zo=10kQ (4 V typ. @ 500W) 13 Powercontrol ExtemalRFoutput control. 0-5Vto full scale, low impedance The term V0 signal and control : DB25 female connector, ontherear e o o e e e o 9 panel . PAGE 6 3 INSTALLATIONANDUSE 3.1 FOREWORD T0 INSTALLATION Although inmostcases no special instruments are required,have skilled personnel inshllthe Unit. To make best use of the Unit’s capabilities and prevent damage to the unit, comply with the recommendations throughoutthis manual. Whenindoubt, orifanytechnical problems should ariseduringthe installation prooedure,Nioom strongly recommend the Unitnot to betamperedwithinany waybyunskilled personnel andwillbe gladto supply qualifiedafier-sale service. As arule, the user should nothave accessto the inside of the Unit fornormal installationand use. Tampering withthe factorysettingsmakesthewarranty voidandmiglrtalso afi'ectUnit’ performance, causing costlydamage. w WARNING! NO ADJUSTMENT OR INTERNAL PRESETTING IS REQUIRED FOR NORMAL OPERATIONS. THE UNIT SHALL BE PROPERLY GROUNDED AND BE OPERATED WITH ALL THE COVERS CLOSED TO PREVENT ELECTRICAL HAZARDS l'N OPERATION AND FULLY COMPLY WITH CE EMI AND SAFETY REQUIREMENTS. NEVER TOUCH THE INSIDE OF THE UNIT WITHOUT FIRST DISCONNECTING IT FROM TI-HE MAINS. DANGEROUS AC, DC AND RADIO-FREQUENCY VOLTAGES ARE PRESENT INSIDE AND BECOME ACCESSIBLE WHEN THE COVERS AREREMOVED. PAGE 7 3 .2 PLACINGTHE UNIT InstallUnitinadi—y,shelteredbutwell-ventflatedtoomawayfmmdustmoisnuejnsectsandvermin (mice). PlaceUnit as closeas possibleto the antennato prevent excessive povmloss in the cables. Ifthis is notfeasible, use antennacables of suitable cross-section. Room sizeshallbe suchthattheUnitcanbeplacedinanuprightpositionandmattechnicalpersonnel caneasilycanyomroutineorextraordinarymaintenance.Theminimumrecommendedsizeistm x 2m, aud2i2m high when there is no otherbroadcasting or support equipmentnearby. The roommust be ventilatedto ensure that the inside temperature never exceeds 3 5°C. Even if 45 °C is the max. allowedtemperature: it is anyway suggested notto approachto this limit. This condition cannot generally be metwhenthe exhaustcooling air is notpushed ontside and is fed back into theroom. This is eventruer ifmore than one Unit is installed in the same location An efficientventilationsystemisthusrequired inthemom Airexchangeinthe roomshall have aminimum flow-rate of 500 metres cubed per hour ormore. If the Unit is fitted in a rack system, the back door of therack cannot usuallybe fixed inplace. If aoompletelyclosedassemblyisneeded, asuitable ventilationextractionmitmustequipthe system. Toaid air ducting, anoptional flangemaybe retrofitted on the ventilation outletto which aduct can be attached to conveyhot air outside. Inthis case remember that the NA 501 internal fans are low- pressure units: some sortof external air-extraction bloweris than imperative onthe exhaustairduct. Vents in the walls and any otheropeningsshall be fitted with ametal grating to keep rodents out, and with a dust filter. Make absolutely certain thatno water can seep through the vents or the air exhaustductor antenna-cable grommet, andthat the floor cannot be floodedduringheavyrainfall. If notimpeditedbyproper airfiltering, insects insomelocationmaybe oonveyedinti'ieintemal heatsink, accumulating onitand finally obstmctingit, causingovertemperature alarm. Evenmoistureand/ordustwhenoontainedintheairorintheroominexcessivequamity,maycause condensationbuild-up intheamplifier. Whenthesystem is periodically switchedon and ofl',thiscan triggerdestructiveelectricarcsandshortcimfitsandtbuscausedamagethatisnotcoveredbythe guarantee. PAGE 8 3.3 WIRING INTO THE MAINS TheNA 501 is powered by a single-phase line. Mains capacity must be at least 2kVA and the nominal voltage is 230Vac. In some countries, where 1 1 SVac is the norm, this voltage must be internally set inthe factoryorby sldlledpeoplebefore installation. While the power supplyregulatoraccepts awide input voltage (1 90 + 250 Vac), operation near the lower inputvoltage onhigh impedancelines must be avoided: iftheline dropsmorethan 10 volt atfull load, the lowline sensecircuitrymaytfiggeranoscillatingtum-on/tum-ofi‘cwle, which is very dangerous In this cases adopt an external line stabiliser. The nominal mains inputrange(190 ~:— 250 Vac) is achieved when the primary side of the main transformer is wiredto the230 V tap. Two othertaps, the firstone slightly lower (20 V), the second higher (240 V), are available to adjust the input voltage range oft l OV, lncountries were a stable 240V is the norm, it is important to set thistap onthe transformer. Inthis case the allowed voltage rangewindowmust be shifiedhigherto avoidnuisance trip at occasional highermainsvoltagez See propersection in the service sectionof this manual‘ To ensure properoperationandcomplywiththesafetyregulations,eficiem earthlingisrequired. Usetheyellow/gleenleadinthepowercable.Thecable’sneutralleadisblue.Neverconnecttheearth to themains’ neutral lead. The cable connectingtheNA 50] mains inputterminal blockto the extemalboardshould consist of leads of adequate cross-section. Recommended values are 1.5 to 2.5 mm squared. Do never switchthe Unit on without antennaconnection, evenwhennoRFdn've is on. 3.4 ANTENNA CONNECTION An "N" outputconnector isfittedat thebackoftheamplifiermodule. ltisveryimportamto check that the antenna, the connecting cables andthe connectors are suitable for 500W. The antennacouplertoo, should be capable of adequate power; its input connectorshallbe "N" PAGE 9 3.5 LFCONNECI‘ION To maximallyavoidearthloops, wirethe modulationsignal line directlyonthe exciter,withhigh quality shielded and preferablybalanoed cable. Ground the shield only onthe exciter LF input 3.6 OTHERRECOMMEN'DATIONS Theambienttemperatureshallrangebetween-5°Cand+30°C(35°Crnax. peak). Itisadvisable to hangamimmax thermometeronthewall to displayany variation. Airconditioningat20+25°CWOuld obviouslybethebest solution, but installation and operating costs are generallyexeessive. Thermal isolationand efflcientventilationwith athermostat—cona'olled blowerare generallythe most advantageous solution. Mains fluctuationandelecu-ic discharges duetothe weather or nearby industrial machinery may cause significanttrouble, especiallyinmountainareas and inplaces close to industrial areas. Insuch cases, it is advisable if not indispensable, to install aprotector, and insulating transformer or possibly an electromechanicalmains voltage regulator.NICOM can provide allthese accessorieson request Since the total oost of the plant, inclusive of broadcasting equipment, antenna system and installation, is ratherhigh, acertain percentage of the budget should be estimated forbuying and installing suitableprotectionandoonditioningfacilitiesasdmribed above Dependingonlocation,theshareoftotalcostshouldbearound20+30%;withthis expenditure, however, themachinerywill opemteunderoptimumconditionsjtsusefirl lifespanwill increase and, aboveall,the incidenceofaccidentalbreakdownsduetoambientorrnainstroublewillbereduced. PAGE 10 !! WARNING ! Q‘ OPERATION WITHOUT THE ANTENNA OR WITH A FAULTY ANTENNA CONNECTION MAY CAUSE DEGRADATION AND POSSIBLE DESTRUCTION OFTHE FINAL STAGE. THIS FAILURE IS NOT COVERED BY THE WARRANTY. AVOID TO USE TOO POWERFUL EXCITERS. AN INPUT POWER HIGHER THAN 12W MAY PERMANENTLY DAMAGE THE RF TRANSISTOR CAUSING A COSTLY DAMAGE, WHICH IS NOT COVEREDBYTHE WARRANTY. A STABLEANDPROPERLY REGULATED 20+25WEXCITER, LHCE NICOM‘SNTZOor NT30ARETHE BEST CHOICE. NA 501 drivenbyatypimlNICOM exciter generates averyclean RF output. Neverthless if any strongRFsigml,comingfi'omnerbyu'ansmittersisooupledtotbeantennntmaycauseintermodulation inthe output transistors and generate spurias. In this case a tuned output filter may be required to remove the problem. It is mandatory to provide adequate ventilation to the Unit to maintain its internal temperature as low as possible, in the recommended range 5 2— 25°C. Even if the Unit may sustain 45°C, and occasionallyslightlyhighertemperaturesmis lifeexpectancywillbeimpaired byhightempemture. As general rule the life expectancy may be halved by each 10°C increase in ambient temperature, over 30°C. PAGE 1 1 3.7 OPERATION Checkthatthe antenngthe subsequentpoweramplifierora suitable dummy load is connectedto the amplifierRF output lftheNA 501 drives atunedtube amplifier, checkthat the inputof the power amplifier is already tuned on the wanted frequency. Control that the power cords are correctly connectedto the amplifier and its driverandboththe Unitareofi'. Beforeoonnectingto the amplifier, control thatthe exciter power is set at zero ora verylow level (<1 W) and the frequencyis correctly set‘ Checkthatthe exciter output signal is fedto amplifierinput, then: 1) Switch-on the power-on switch on theNA 501: - the switchwill glowred. - Intemalblowers will start. - No led should lighten. - No RF output power should be present. 2) ProperlypositionthemeterswitchtoobservetheRFoutputincreasingonthe amplifier. 3) Switch-on the power-on switch onthe exciter 4) Slowly raise the drive power to the required level, i.e. 8 + 10W. - The RF output power should rise fromzem to the nominal 500 Watt, if the output power adjustmentis set is to maximum ontheamplifierfi‘ontpahel. - No led should lighten. - As a general rule, the inputpowermustbe 20%higherthanthe minimum level required to the full output power (i.e. 8W if 10 W are enough to obtain 500W on the output). 5) Control andnoteforfuturereferencethecorrectreadingoftheoperatingparametersthroughthe intemalinsmnnentation, whichrnustindicatethefollowingvalues: ~ FORWARD POWER: up to 500W - REFLECTEDPOWER: < 50 W, typl 0 + 20W - REGULATED VOLTAGE: 48V (300V meter range) ~ UNREGULATED VOLTAGE: 140V 11 5% Some amplifiersdo notpermittoreadtheregulatedandiuuegulatedvoltage onthe intemalmeter. The installationof the amplifier is thereby completed. A spectrumanalysis is nowadvisableto assureno spurious productsdueto intemalorextemal causesaemeverseinterrnodulationonthefinal stage) are generated. Nicom wishes you success in your work andremindyouthat they are always available forfurther informationotto tackle anyspecific problem. PAGE 12 3.8 POSSIBLE MALFUNCIONS Noledalannmustbeonduringregtflarfimcfioning:followingisalistofpossiblemalfimcfionscausesi "VSWR" led on Thisledtums onwhenthereflemedoutputpowerexceedsthe40-50Wfl1resholdiInthiscase,do not operate the system and check antenna, relevant wiring and connectors. WhentheUnitisoonnectedtoasuocessiveamplifier,re—nmemelaner‘sinpmtoobtainfliemallm reflectedpower. This light should nevertumon; it mighthowever flashbriefly at lowpowerwhen firsflytuning the input of an NA 501 -driventube amplifier or a cavityband— -pass1 filter "Temperature"led on Thisledtumsonwhenthemtemaltemperatmeisexoessivexedueeenvimnmemtemperamreand increase room ventilation lnthis case, itis importantthat the hogairreleased bythe Unitbe exhausted. Contohegularfimcfioningoffliemtemalvenfilationfansandcleananyextmiallyapplieddustfiltet, ifany. PAGE 13 4 SERVICEAND MAINTENANCE Sincethe NA 501 is cooled by air, it is subject to clogging bydust. Because ofthe high-quality materials usedintheirmanufacture, ifit is installed asset forthunder“lI\ISTAI.LATIONAND USE,” itwill notrequire special maintenance forquite some time. Aregularserviceroutine,mainlytoremoveintemaldustissuggestedoverafimonthtoayearrate. Take present that 90% oftheaircirculation isrestrictedtothemalnintemal ventilationchannel and do notaffectthecomponents. Regularlychange the venfilafionfanespeciallyinhighertemperature mvimnmentsAZ—yearratemaybeprudenfial:alwaysusethesamehighquality,ballbearingfimtype. Afierafew years of continuous service, it is recommended that the Unit be overhauled in the factoxyorinaspecialisedlaboratory,wherethecharacteristicscanbecheckedagainsttheinitialones and recalibration can be made whenneeded. It is also especially importantthat the power supplybe over-hauled whemheUnithasbeenworking at high temperatures, over 30 -1- 35°C. Never change orcausethe original settingsto be changed whenthenecessary, complex testing equipment and standard calibration procedure are notavailabler 5 WARRANTY Like all NICOM's solid state equipment, the NA 501 carries a 2-year Warranty on all its oomponentswiththeexclusionofthefinalRFpowermodule,whichmaybedamagedbyfiaultyoutput connections. ‘ Thiswarranty isnullaudvoidiftheUnitistamperedwithoriffailureisdueto irnproperuse, wrong mstallationorextemal causes, suchasmains overvoltage. This warranty covers work done exclusively in our laboratories and in those of our agreed representatives. ' \ The goods shall be delivered carriage prepaid to the laboratory and shall be returned freight forward. This warranty does notcover any consequential damage dueto non-operation or fiasulty operation PAGE 14 6 SERVICE MANUAL 6.1 SYSTEM DESCRIPTION 3 basic sections compose the NA 501: the RF amplifier box, the power supply and the control and metering section . TheRFsectioncomprises 1x500Wamplifiermodulesoonnectedthroughsnip-llnecombiners. All theRFtransistorsare Mos-Fet type. Alow-pass filter with directional coupleroompletes the section, whichiscompletelyscreenedbyametalbox,tooomplywithEM]requirementsAfirllyplanardesign permitsanimmediateawessandinspectiontotheZintemalmodules. The power supply comprises a mains transformer, whose output is rectified and filtered and a highly efficient Switch-Mode Power Supply regulator. The RF control section is built on one small board. It performs RF AGC arid protection control; providing metering and an interface to the external I/O port. Bothdirect and reflected power are displayed and provided as proportional analog signal atthe Remote l/O port. Through this port is possible aswellto commandthe RF output power, overcomingthe internal front panel regulation. 6.2 INTERNALDESCRIPTION 2:5".- m... k ”a 14mm 0mm emlmr m- m.» n: mm m. e - - r 9 Amman MODULE mm m / m we.» mum m. .. "w. M,“ . ”mm “mm ‘ _ "M rum m- m... , mm. m. mam (m. m m MW. “an, vnlw m. um. r w-Hw «Mm . m n... no»; Nut “my Quin; bu- vowsn sumv r. CONTROL NA 501 : Block diagram PAGE 15 The NA 501 amplifier comprises 6 internal different modules/boards plus some spare mp0nents,ascanbeseeninfl1edrawingoftheinnercontentsandinfl1e"Generalwifingdiagmm"; both comprised in this manual: -The power supply transfonner, rectifier and capacitor -The Switch Mode Power Supply regulator -The RF control and measure board -The input RF power splitter -T'he SOOWRF power amplifier module -The output RF combiner, Low-Pass Filter and coupler For the detailed description of each module on the following pages, always refer to the corresponding electrical diagram, in the relevant section of the manual. “ THIS SECTION IS ONLY AIMED TO GENERAL KNOWLEDGE OF THE UNIT AND FOR SERVICE PURPOSE BY SKILLED PERSONNEL. AS EXPLAINED IN THE PREVIOUS SECTIONS, INTERNAL ADJUSTMENTS ARE NOT REQUIRED DURING NORMAL OPERATION. TAMPERING WITH INTERNAL SETTINGS VOIDS Tl-HE WARRANTY, MAY HARM THE UNIT AND JEOPARDIZE THE GUARANTEED PERFORMANCE. IN ADDITION, MANY MODULES ARE TOO MUCH SPECIALIZED AND ‘DIFFICULT TO REPAIR EVEN BY SKILLED TECHNICIANS AND MUST BE REPLACED IN CASE OF NEED BY BRAND NEW ONES AND POSSIBLY RETURNED BACK TO FACTORY TO VERIFY IF THEY CAN BE REPAIRED. ANY ISPECTION ON THE MODULES DESCRIBED ABOVE MUST BE EXECUTED WITH THE TOP COVER REMOVED AND OFTEN WITH THE OPERATING UNIT CONNECTED TO THE MAINS. ALTHOUGH MOSTLY OF THE PARTS UNDER VOLTAGE ARE INSULATED AND ARE NOT EASILY ACCESSIBLE, THIS EXPOSES TO THE RISK OF ACCIDENTAL CONTACT WITH THE MAINS VOLTAGE. TO AVOID IT, ALWAYS USE INSULATED TOOLS AND NEVER TOUCH THE SUPPLY TRANSFORMER, THE MAINS SWITCH OR THE MAINS SOCKET WITH MADIS CONNECTED. NEVER OPERATE THE EQUIPMENT WITH THE COVERS REMOVED. REMOVAL OF THE BOTTOM RF COVER MAY LEAD TO lMPROPER FUNCTIONING OF ANY ELECTRONIC MEASURING METER DUE TO HIGH RF FELD. — MAINS VOLTAQE MAY KILL! — PAGE 16 6.3 The pgwersupply components The power supply components, other than the boards below described, are very few: mainly the power transformer with a power relay, a bridge rectifier and a power capacitor, which delivers the raw rectified dc power to the SNIPS regulator module. The unregulated dc voltage, nominally 140 Vdc, may range 120 + 170 V. The primary tap on the power transformer is factory set on the 230V input, allowing a mains range approximately 200 + 250 Vac. Should the mains voltage be 240Vac nominally, it is suggested to change the transformer tap to that voltage. If the mains voltage is a stable 215 + 225 Vac, the transformer tap may be lefi as factory set. Only if there are fi'equent occasional drops of mains input below 195V and consequent system stops, it is suggested to lower the input tap to 220V. To do that, the power cord must be disconnected from the mains, the top cover must be removed and the transformer voltage terminals may be accessed. An USA version is provided with a someway different transformer and general wiring (see the appropriate electrical diagram and internal layout) In this version, some jumpers must be preset on the equipment s internal terminal board ”FBI to provide 1 15 or 230Vac operation, if not factory wired. In details these settings are: 220 Vac l/P3 to 3/P4 115 Vac 3IP3 to 3/P4 and l/P3 to lIP4 6 .4 The Switch Mode PgwerSupply regulator This module performs an efficient regulation of the raw dc input, nominally 140V :l:15% to a lower 48V il%. Being is efficiency veryhigh, vm'y little heat is produced inthe regulation process The nominal current capability of the regulator is much higher than requested, and approaches 40A @ 48V. A control I/O connector on an upper daughter board pemrits a remote control of the regulator NA 501: Positioning of the power supply internal terminal board ' PAGE 17 by the Unit controller, i.e. output on/stand-by, crurent and voltage monitoring, status prompting and alert. A fast 80A semiconductor-grade protection fuse is screwed on the board: it may be fused by the crowbar protection in case of switching transistor damage. If this happens a first attempt to replace the fuse may be accomplished, afier having verified the integrity of the power transistors Usually something is broken so causing the fuse blow-up. Reparation of this module in the field is very difficult if any component other than the fuse and/ or a power transistor failed. It is suggested to substitute the module with a new one and send back the damaged unit to the factory for inspection and possible reparation. 6.5 TheRF control and measug board This small board canies all the circuitry to control and protect the RF amplifier mge. Let us consider its various loops. Two identical bufiers, lC4aand IC3a, insulate and amplifythe directand reflected signal detected on the RF output coupler, with difi'erent gain The main direct power regulator loop is built around the subsequent IC4d op-amp, which compares the sensed signal with the preset power level on RT5. Adjusting this trimmer, the RF output power may be varied to values different from that factory preset. Never exceed a safe 500W on RF output, even ifthe amplifier is usually able to easily threpass this limit, to have some safety margin The output of [04d consumes the AGC line, which is buffered by IC5 to drive the RF transistor gates. Both the two sections of ICS are in parallel to increase the current capability of the external AGC line. The reflected power protection is managed by IC3c, which compares the reflected sensed signal to a fixed threshold, which is set to 40/50W, as determined by R35 and R36. The output of IC3 adds on the internal AGC line though D14. The action of this circuit is proportional: i.e. the output power is continuously decreased till the fraction which is reflected back no more exceeds the safe maximum level. There is no RF complete switch off even with severe load mismatch. Both direct and reflected signal lines are conveyed to the remote connector through insulating lOkohm resistors The temperature protection on the output stage is performed by IC4b, which hips when the temperature sense line crosses its preset threshold, completely disabling the RF output The tem- perature sensor is mounted on the heatsink, near the RF transistors, and is constitued by a precise PTC resistors, which varies its resistance accordingly to the temperature. PAGE 18 On this board a small negative rectifier and a regulator (TR5) provides the negative bias to completely disable the RF power, if needed. The positive regulator TR4 derives the positive 1 1 .3V board supply fi'om the +48V regulated line. 6.6 TheinputRFpowersplitte: The purpose of this simple board is mainly to divide the input RF drive power in two identical signals, one for each power amplifier module, providing a good insulation between each output port (>20 dB, typ. 23 dB minimum on the whole FM band) This is done by a Wilkinson type printed coupler, followed by the balancing resistor array R21 + R24. A directional coupler senses the input RF level and RT1 is regulated to provide the overdrive protection circuit trip at the right maximum input level. The board supports also the direct (or forward) and reflected detector sensitivity trimmers, whose input comes hour the output board. Two additional lines support the RF module bias (or AGC) line and the temperature sensing PTC thermistor. 6 . 7 The RF power amplifier module This module is built around a couple of "Gemini type" Mos-fet transistors each one forming a 300W push-pull amplifier. Discrete Wilkinsonvtype couplers equip both the input and the output module section, doing the job of dividing and recombining the input and output signals, providing a suitable insulation between the transistors. A small balancing resistor R1 is mounted on the input splitter, while a much bigger resistor R14 is mounted in the output combiner. A group of C, R and L RF decoupler and dampening components are mounted on the positi- ve supply line of each amplifier, plus a small value mismr, R12 and R13, for possible separate current detection of each supply leg \ The gate bias is separately adjusted through R15 and R16 on each section. Do not tamper the factory bias preset values! The full power output of the whole module exceeds 600W, to provide some room for coupling losses on the combining stages of higher power amplifiers, likethe sameNA 501. PAGE 19 6 .8 The ougutRF powereombiner, LPF and coupler This module is symmetric to the input power splitter and is another printed Wilkinson coupler, whose power management capability is obviously much higher than the input board‘ In this case the power balancing resistors are high power devices, whose centre connection is referred to ground through an inductor, which discharges any static electricity on the antenna up to a relevant amount of powerr The power combiner is followed by a printed low-pass filter, which attenuates the harmonic products generated by the amplifiers. 3 directional sample lines derive two rectified voltages proportional to the direct and reflected output power and a RF signal for external monitoring purposes. PAGE 20 7 REPAIR AND REPLACEMENT OF DAMAGED MODULES The NA 501 is a high reliability Unit, as much effort was done in the design and development stage to assure the maximum reasonable working margin for each part, Nevertheless, as all Unit which works 24 hours a day for years, some failures are possible, especially in those environments which over-stress the Unit, like hot or dusty or moist places, or subjected to wide mains fluctuations or static discharges and things like that. In the event of any failure an appropriate analysis must be done to avoid subsequent failures due to faulty ambient conditions. A ofien underestimate cause of failure is simply a too high ambient temperature or insuflicient ventilation. Improving the ambient and system ventilation as suggested inthe installation paragraph of this manual, usually fix the problem. Other obvious causes may be dust clogging and ventilator fan failure, A regular service and maintenance routine will avoid these sources of problems and it is suggested to change the ventilator each two years, even if no damage is still visible, eSpecially at high ambient temperature . No air pipe must be attached to the ventilator fan output for air ducting, If an external extacting fan rs not installed m that system In any case, if the amplifier fails, some work must be done on the Unit to fix the problem. With the appropriate spare parts, most of repairing work may be done on site, without need of special tools and ofien without need of any solder joint Not much needs to be said about the general boards and components changing: virtually all of them may be changed in few minutes, without retouching the adjustments. Most of them are immediately accessible or needs a minimum of dislocation of other components and plates. Only the RF boards need a deeper look. RF boards are delicate modules, which contains some parts as flanged power transistors and resistors which must separately be screwed on the supporting heatsink and may be easily damaged by improper handling. These boards are the 500 W power amplifier modules and the RF output combiner. Repairs ofthese modules are usually made inthe factory or in a specialised laboratory, if possible at all. If the pc board is damaged perhaps only the costly RF active devices may be recovered. Nevertheless, very ofien this is worthless because, in case of major damages, these parts are internally electrically damaged or degraded Repair of the RF modules requires too, at the end of the rcparation, a full check of the module's working parameters in a dummy fixture or in a test assembly which are not available even in most specialised laboratories For these reasons repairs of the modules, specially the higher power amplifiers, is discouraged at the most and the broken one must be replaced by new parts with the PAGE 21 same identical characteristics, fullytested at the factory. To replace the modules avoiding as much as possible to damage the new part or the old transistors, if not already broken, carefirlly follow the subsequent steps: 1) Remove the amplifier cabinet from the rack, alter having disconnected fiom its rear connectors the RF input and output cables, the power supply and the control cables. Disconnect also the ground cable from its screw. 2) To investigateonthe damagedpan‘s ortotestthereparation, itmayberequiredto externally connect the removed cables and the RF output load to the amplifier assembly in manner to permit inner inspection of the top and bottom of the Unit. Ifthe latter is placed on a small stand aside of the main rack, the internal cables are usually long enough to permit the connections, avoiding extension cables 3) Open the bottom cover of the cabinet and remove the screen from the damaged module(s), if any. 4) If the damage is not immediately visible, it may be helpful to measure the currents sunk by each 300W sub-module amplifier. To this aim a low ohmic value shunt resistor is inserted in series to the 48V power supply of the module's subsections (R12 and R13, 10mg). To measure the current sunk, the amplifier assembly must be completely connected and powered with and without RF. A sensitive, RF proof, digital voltmeter must be used to measure the voltage across the shunt resistors, which vary from nearly 1 mV at no load to 100 mV at full power. T__ake care: most of low quality digital or analog meters are not able to do this reading, because they are afi'ected bythe high RF field and their reading rs completely meaningless! WARNING. great care must be paid not to accidentally short-circuit the resistor leads to the ground with the voltmeter probe tips, dming the measurements! 5) When properly functioning at full power, each module 300W subsection will sink 8 + 10 Amperes, i.e. 80 + 100 mV across the shunt resistor. The absorption must be balanced i10% around the mean value on each amplifier. A lower or higher value may mean a module failure 6) Remove the power supply cable screwed on a centre terminal in the board and the small bias cable. 7) Unscrew the input and output RF connections, at the module opposite sides. 8) Carefully unscrew the RF transistor flanges fromthe heatsink base-plate. This operation, if not properly done, may mechanically over-stress the transistor, cracking the internal de- licate beryllium-oxide ceramic which supports the active silicon dies and determine unrecoverable PAGE 22 damage of the device. CAUTION: beryllium-oxide is toxic and must not be thrown with domestic refitse but in specialised toxic material disposals. No special handling precaution must be paid when the transistors or power resistors are not mechanically broken, apart those deriving from the handling of mechanically fragile (and very costly) devices. Ifthe transistor or resistor flange is broken, avoid to get in touch with it and the brittle white exposed internal ceramic or inhaling dust of it Dispose the transistor or the entire broken module as previously described. 9) Make a note of the position and the length and remove the threaded screen spacers and the board fixing screws. 10) Remove the broken module and clean the supporting heatsink base-plate before mounting the new one. 1 1) Smear thin heat—conductive silicon grease below the flanges of the power transistors and resistors of the new module, before mounting it. 12) Position the new module, placing the threaded spacers and screws over the p.c. board avoiding to tighten them. When all the screws are placed, control the correct alignment of the transistors and resistors fixing holes and tighten the screws and spacers. 13) Insert the proper screws and washers, if any, across the transistors and resistors and carefully tighten them in several, alternate steps. 14) Reconnect the power supply and bias cables to the module. 15) Tum-on the whole amplifier fully connected to the supporting power and control rack without RF power, with RF load connected and driver exciter off. Enable the equipment, with the exciter still off 16)Measure the bias current of the two transistors on the module, as explained on previous paragraphs 4 and 5. They were factory adjusted to 100 mA (lmV). 17)I.fthe mil-rents are ofi'the range 50 200 mA (0. 5-1- 2 mV), carefully retouch the bias trimmers on the board. A small clockwise rotation increases the bias current. 18) Reduce the output set power to a low value, acting on the front panel power set trimmer and turn on the exciter power. 19) Slowly increase the power-set and measure the balance of the current drained by each module at halflevel and at full power. Verify the limits written in paragraph 5. PAGE 23 20)Turn off the equipment, reassemble the screening covers and the bottom panel of the Unit and reposition it in its working location with full connections. 21) Perform a limited period of test at fixll power, i.e. 500 + 550 W and then reduce power at maximum nominal working level, is. no more than 500 W. PAGE 24
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