Galanz WP700AP17 User manual

Galanz
MicrowaveOven
MODEL: WP700AP17, WP700AL17-K4
WP800AP20,WP800AL20-K4
Service Manuał

INTRODUCTION
ThisMicrowaveOven Service Manuałisprintedina loose-leafformat.Eachpartisdividedintosectionsrelating
toa generałgroupofcomponentsandeachsectionissubdividedinto various parts describinga particular
componentor service procedurę.
Thesubdividingofthesubjectmatterplusthelooseleafformwillfacilitatetheupdatingofthemanuałasnewor
revised componentsand service procedures arę introduced.
Eachpageofthis service manuałwillbeidentifiedinthe Iower righthandcornerand,asneworrevisedpages
arę published,itwillbeeasytokeepthemanuałupto datę byfollowingthe filing instructionsonthecoverletter.
This Service Manuałisa valuable service tool andcareshouldbetakentokeepitupto datę bypromptand
proper filling ofsubsequentpagesasthey arę issued.
CONTENTS
SAFETYPRECAUTIONS2
1THEHEATINGPRINCIPLEOFMICROWAVE3
2THE STRUCTURE AND WORKING PRINCIPLE OF MICROWWAVE OVEN4
2.1 HIGH VOLTAGERECTIFYINGCIRCUIT.4
2.2MICROWAVEGENERATER5
2.3COOLINGSYSTEM5
2.4ELECTRICCONTROLSYSTEM5
3TYPICALCIRCUITANALYASISOFMICROWAVEOVEN8
4 HOWTO ASSEMBLEANDDISASSEMBLEMICROWAVEOVENCOMPONENTS9
4.1THE GABINET 9
THEDOORCOMBINATION10
4.3THECONTROLPANELANDTHEDOORRELEASEMECHANISM11
4.4 THEMAGNETRON 11
4.5THETRANSFORMER12
4.6 THE FANMOTOR12
4.7 THECAPACITOR 13
4.8THEDIODĘ13
4.9 THETURNTABLECOMBINATIOM 14
4.10THEDOORSAFTYINTERLOCKS14
THECONTROLPANEL OF A TYPICAL MICROWAYE OVEN15
5 BREAKDOWN ANALYSIS AND THE MEANSOFOYERHAULING 16
5.1EXAMININGTHEBREAKDOWNCAUSES16
SPOTEXAMININGSTEPSOFTHEMICROWAVEOVEN 16
5.3REPAIRINGMETHODOFSEVERALBREAKDOWN19
5.4THECHARACTERS REOUIREMENTS OF MICROWAYE AFTERITHASBEENREPAIRED20
6CRITICALPARTS SERYICING 21
6.1IMPORTANTTHINGSTODO PRIOR TOCRITICALPARTSSERVICING:21
6.2InterlockAssemblyReplacementandAdjustment21
7COMMONBREAKDOWNOF MICROWAYE OVENANDMEANSOFREPAIRING......22

SAFETY PRECAUTIONS
PRECAUTIONSTOBEOBSERVEDBEFOREANDDURING
SERVICINGTOAVOIDPOSSIBLEEXPOSURETOEXCESSIVE
MICROWAYE ENERGY
A.Donotoperateor allow theoventobeoperatedwiththedooropen.
B. Mąkę thefollowingsafetycheckson all ovenstobe serviced beforeactivatingthemagnetronor
othermicrowavesource,and mąkę repairs as necessary.
(1). Interlockoperation
(2).Properdoorclosing
(3). Sealandsealing surfaces (arcing, wear, andotherdamage).
(4).Damagetoor loosening of hinges andlatches.
(5).Evidenceof dropping orabuse.
C.Beforeturningon microwave powerforany service testorinspection within themicrowave
generating compartments, checkthemagnetron,waveguideortransmission linę, andcavityfor
properalignment,integrity,andconnections.
D.Anydefectiveormisalignedcomponentsinthe interlock, monitor, door seal andmicrowave
generationandtransmissionsystems shall berepaired,replaced,oradjustedbyprocedures
describedinthismanuałbeforetheovenisreleasedtotheowner.
E.A microwave leakagechecktoverifycompliancewiththeFederal performance standardshouldbe
performed oneachovenpriortoreleasetotheowner.
THISMANUAŁ,ASWELLASTHEINFORMATIONCONTAINEDIN IT, ISTOBEUSEDONLYBY AŃ
AUTHORIZEDSERVICE TECHNICIAN FAMILIARWITHANDKNOWLEDGEABLEOFPROPER
SAFETYAND SERVICING PROCEDURESAND POSSESSING HIGH OUALITY TEST EOUIPMENT
ASSOCIATEDWITH MICROWAVEAND ELECTRICALAPPLIANCEREPAIR.
ALL INDMDUALS WHOATTEMPTREPAIRSBYIMPROPERMEANSORADJUSTMENTSUBJECT
THEMSELYES ANDOTHERSTOTHE RISK OFSERIOUSORFATALINJURY

1THEHEATINGPRINCIPLEOF MICROWAYE
Microwaveisonekindofradiowavewhose wavelength is very short, frequencyis very high.Therefore,itis
called ultrahigh frequencyelectromagneticwave.Microwavecanheatfoodmainlyresultinthe mutual affect of
thefoodinthemicrowave field andthemicrowave field itself.
Undertheaffectofmicrowavefield,thethermal effect mechanismproduced from themutualaffectofthe
microwaveandthefoodincludes two aspects.OneisDielectric loss ofpolarmolecule;theotheris conductive
loss ofion.
Usually,foodisconstitutedoforganism(plantandanimal).Theorganismisformedby all kindsofpolarwater
molecule, polarproteinmolecule,andall sorts ofsaltion.Thecenterofgravityofthepositiveandnegativecharge
inthemoleculeisnotcoinciding.Innormalcondition,themoleculeisinirregularorderduetoitsthermalaction,
thus thefooddonotappearpolarity. (FIG. 1-la). Undertheactionofouterelectric field, thepositiveendofthe
polarmoleculetrendtothenegativeelectricfield,thenegativeendofpolarmoleculetrendtothepositiveelectric
field,andsomewhatarrangeinorderthroughthedirectionoftheelectricfield(FIG. 1-1 c).Thisphenomenon
usuallyiscalled "TORGUE POLARITY".Whentheouterelectricfield apply fortheopposite polarity, thepolar
moleculethenarrangeanoppositedirectionorderaccordingly(FIG. 1-1 b). If thedirectionoftheouterelectricfield
changedrepeatedly,thepolarmolecule would repeatedlyswayaccordingly.Duringtheswaying,itis
understandingthatthepolarmoleculewouldproduceheatduetosomewhatsimilarfriction among them. When
theelectricfieldisappliedforultrahighfrequentmicrowavefieldfromtheoutside,itsdirectionwouldchangetens
billion times persecond,sodothemolecule.Thiskindofmoleculeswayingproducingsimilarfrictionalheatfrom
the interference andbłockoftheactionstrengthamongthemolecule,andchangedtomicroscopicmicrowave
heating. Microwave heatingnot only concernedthenaturęofthematter itself, but also closelyconnectedwiththe
electricstrengthandfrequency.WhenthefrequencyisIow,themoleculeswaying ratę andtheacutedegreeof
themutualfrictionamongthemoleculeisIow,andwouldproducemuchheat.Whenthefrequencyistoohigh,as
theswingofthepolarmoleculeiswithrotating inertia, it madę theswingdonotin linę withthechangingrhythm
oftheelectricfieldbecauseofthefriction drąg, thus,actually Iowed thepolarmoleculeswayingspeed.The
frictiondraggingdegreeisconcerningaboutthemagnelectricwavefrequency,polarmoleculeshape,andthe
matter's stickydegree.Todifferent matter's molecule,thereisdifferentspecialfrequency żonę. Thoseabsorbing
microwaveenergyfromthis żonę arę mostcapabletoturnmicrowaveenergytoheatenergy.
(a)
(b) (c)
Fig. 1-1
Apart fromtheabovesaid action, thereisanotheractionwhichiselectricionundertheactionof microwave field,
actfiercelyaccompaniedwiththeaccelerationofelectricfield.Thepositiveiontransfertothenegativepolarityof
thefield while thenegativeiondoesopposite.Accompanyingwiththechangingelectricfield,theelectricion
hangingaccordingly.Duringthetransferring,heatproducedwiththecrashamongtheion.Thiskindofaction
takesthe main effecttothosemicrowavesheatingofhighsaltmolecule.
Nomatteritisthepolarmoleculeswayingortheiontransferring,theyboth arę turningthemicrowaveenergy
whichtheheatingmattergotfromthemicrowavefieldtoheatenergy.Fromtheanalysisoftheory,wecandraw
such a conclusionthatthepowerwhicha unitofvolumematterabsorbedfromthemicrowavefieldasthe
followingformuła:

Pa=KE fErtg 5
PaStandsforthepowertheheated matter adsorbed from themicrowave field.
KStandsfora constant
EStandsforthe microwave frequency.
fStandsforthemicrowave frequency.
tg6 Standsfor loss angle tangentoftheheatedmatter.
ErStandsforrelativedielectricconstantoftheheatedmatter.
High Voltage Rectifier
220V
r
2THESTRUCTUREAND WORKING PRINCIPLE OF MICROWWAVE
QVEN.
Microwaveovencanbeclassifiedto many kinds
accordingto various construction, volumeandcontrol
function.Butanyhow,the main electric parts arę all
composedofhighvoltage rectification, coolingsystem.
Microwavegenerator,electriccontrolsystemandheating
chamber (FIG.2-1). Its workingprocess arę asfollows:
220Vpowerfrequencyvoltagetransferredtotherectifier
throughelectriccontrol system, andthenbechangedto
4000Vdirectvolt-agebytherectifier,andbethen
transferredtothemicrowavegenerator,thegenerator
starsworkingtotransferthemicrowaveenergytothe
heatingchamberforheatingfoodthroughwaveguide
tubę. Atthesametime,theelectriccontrolsystemsetoff
thecoolingsystemto cool theworkingrectifierandthe
microwavegeneratortokeeptheovenworkingsteadily
froma toohightemperaturę. If somethingwrongwiththe
coolingsystemcausethetemperaturętoohigh,thecontrolsystemwouldcutoffthepowerautomaticallyto
preventmicrowavegeneratorbeingdamagedformthehightemperaturę. Nów, we'd like tointroducetheworking
principleofeach part ofthewidelyusedmodel,mechanicalcontrolandtouchcontrolmicrowaveoven.
2,1HIGH VOLTAGE RECIIFYING CIRCUIT.
Atpresent, home usemicrowaveovenadoptthishighvoltage rectifying circuitasshownatdiagram2-2.The
circuitisa singlephase,semi-wave,doublevoltagerectifyingcircuit.Thecircuithas only a highvoltagecapacitor,
ahighvoltagediodę,a magneticleakagetransformerbesidesthemagnetron,is very simple.
Theworkingprincipleofthecircuit:220Vpowerboostedthroughthetransformer,outputabout2000Valternating
highvoltagecurrentwhenthehighvoltagewindingisatthepositivehalf-circle,thehighvoltagewindingisatthe
negative half-circle, thediodęiscutoffandthemagnetronisconducted.The electricity chargedatthepositive
half-circleofthecapacitorisseriesconnectedwiththepositivephaseofthewinding voltage, andgota doubled,
about4000Vdirecthighvoltage,thentransferredto between thecathodeandtheanodęofthemagnetron.
Electric Control
220V
Fig. 2-2
Fig. 2-3

2.2 MICROWAYE GENERATER.
Microwavegeneratoristhe heart ofmicrowaveoven.Thequalityofa microwaveovenmostlydependsonthe
qualityofthemicrowavegenerator.A microwavegeneratorismainlycomposedofmagnetronanditspower
supply circuit, FIG.2-3 isthetypical circuit diagramofthepresentusedmicrowave oven's generator.Thepower
supplycircuitiscomposedofrectifyingcircuitandfilamentcircuit.
Usually,weadoptcontinuouswavemagnetron. It canturnthedirectenergywhichisappliedtothemagnetron
after beinghighvoltagerectifiedtomicrowaveenergy,thepowersupplycircuitsupplya direct high voltage
between thecathodeandanodęofthemagnetron,a filamentvoltagetothecathodefilamentofthemagnetron.
Theworkingprocessofthemagnetron:Whentheanodęvolt-agegraduallyrises from zero,theanodęcurrentis
approx.zero, thepoweris very smalias well. Whentheanodęvoltagerisesto "THRESHOLD" voltagevalue,the
magnetron starts oscillating,andtheanodęcurrent would increase obviously, providedtheanodęvoltagerisesa
little morę, theanodęcurrentwouldincreasea lot (FIG.2-4), andwouldreachthe ratę value guickly.
If theanodęvoltageis undulating, itwouldcausetheanodę
currentswingfiercely,even madę themagnetronstoposcillating.
Forkeepinga steadyoutput,thepowersupplycircuitofthe
oven must supplya steaddirectcurrentvoltage.Thefilament
voltageofthemagnetronmustbesuppliedbyanalternating
currentvoltage.For simplifying thecircuit,itwouldbesupplied
bythesameleakagemagnetictransformerwiththeanodę
power(highvoltagepower).Thefilamentofthemagnetron
whichthepresentusedmicrowaveovens arę all treatedthrough
some special technology, andall have the cold start character.
Butwhenincoldstart,there still isa verystrongsurgeelectric
field attached tothesurfaceoftheanodę,andwouldbeharmful
totheanodę.Inordertoreducethesurgevoltage,thefilament
ofthemagnetronmustbeconnectedastheFIG.2-3shown.In
thisfigurę,whentheanodęcurrentofthemagnetroncirculates,
thefilamentcurrentshould flow totheFAendfromthe Iower
end.
2.3 COOLING SYSTEM
4,OJ
100200300400
anodęcurrent
— Ib(mA)
Fig. 2-4
Intheworkingprocessofthemicrowaveoven,themagnetron often makestheanodętemperaturęrisedueto
anodę loss
causedbytheelectronicsstriketheovensurfaceandtheheatradiateofthecathode.Topreventtheanodę
temperaturęrisetoohigh,thus affect theworkingsteadyandits life span,itis necessary to cool themagnetron.
Accordingtothe different modelsand ratę outputofthemagnetron,compellingwindcoolingandflowing
water-cooling canbeadopted.Usually,the home usedmicrowaveovenadoptsthecompellingwindcooling
method, andall arę fixedwithcooling fin.
Coolingsystemincludesfan motor, air duet, airentrance,airventetc.Theflowingdirectionofthecoolingwind
should.Beparalleltothecoolingfinofthemagnetron. Generally, weadoptthemethodofair blast ratherthanair
absorb.Andallthecabinetoftheoveniswithairentranceandairvent,thehotwindblowingthroughthe
magnetronisguidedwithair tubę toimprovethecooling effect. Inthetechnicalparameterchartofthemagnetron,
itusuallywillgiveouttherequirementofcoolingwind.A shortage ofcoolingwindwoulddamagethecharacterof
themagnetron,evenburnoutthemagnetron.Theamountthatthefanblastedshouldnotbelessthanthe
requirement.Whenfixthefan, attention mustbepaidtopreventthecoolwindfromblowingdirectlytothe glass
part ofthemagnetrontoavoidblasting.
2.4 ELECTRIC CONTROL SYSTEM.
Tothosemechanicalcontrolmicrowave oven, electriccontrolsystemmainlycomposesofinterlockswitch,timer,
powerdistributorandthermalcutout,etc.Theelectriccontrolsystemofthosetoughcontrolmicrowaveovenis
mainlycomposedofinterlockswitch,computercontrollerandthermalcutout,etc.

fuse main latchswitch
—-—f
Si
pilot switch\ §3
S2
doorclosedassistantlatchswitch
(a)
Fig.2-5
doorhook
latchswitch
pilotswitch
2.4.1 DOORINTERLOCK SWITCH
Drawing2-5(a) is thecircuitandconstructiondiagram
ofthedoorinterlockswitchofbrand, EMN-109
microwaveoven. It mainlyconsistsof latch switch (S1,
S2),pilotswitch (S3), door hook and starting
mechanism ofthedoorinterlockswitch.
Therefixedhooksontheoven door, andopened two
rectangleholeatthe corresponding placeattherightof
theovenandthehook. Inside eachrectanglehole,
therefixeda micro switch.Whentheovendoorclosed,
thetwohookonit would insert intotherectanglehole,
andjustpushdownseveralmicroswitches.Atthat time,
S1, S2 arę closed, S3iscut off, andthemicrowave
ovenisunder preparation of working. Tothat
mechanicalcontrolmicrowaveoven,nosooneryou
turn thetimeswitchtosettheheatingtimethanthe
powerwouldbe supplied tothebacktostarttheoven.
Tothosetouchcontrolmicrowaveoven,hardlydoyou
settheheatingtimeandpower,andtouchthestart
button whenthepowerwouldsuppliedtothebackto
starttheoven.Whenpressdownthedoorrelease
button, S1, S2 arę cutoff,S3isclosed,andthe
microwave ovenwouldstopoperating immediately.
Provideddueto some mań - madę ortheappliance
itselfreasons,whenthedoorisopen,S1,S2 arę
closed,duetothepilotswitch(S3) still atconducted
conditionwould mąkę the220Vvoltage short-circuited
andfusedthefuse,andwillnever let themicrowave
ovenworkingwhenthedoorisopen. From thiswecan
understandthefunctionoftheinterlockswitchiswhen
thedoorisunclosed,theovenwouldn'twork,whenthe
doorisopenedwhentheovenisworking,itwouldstop
theworkingimmediately(FIG.2-5b).
2.4.2 TIME ANDPOWER DISTRIBUTOR
Timeandpowerdistributorismainlycomposedoftimer
motorandtwosetsofgearswitchS4andS5.When
thetimerisatzero position, thegearswitches arę cut
off,whentheheatingtimeissettled,thegearswitchis
closed.When started theoven,thetimemotor starts
working.Whenitreachesthesettledtime,itwouldcut
offthegearswitch(s4)tosteptheovenworking.The
gearswitch(S5)isdesignedforcontrollingtheoutput
ofthemicrowaveoven,actuallyforcontrollingthe
outputofthemagnetron.Itmainlybythemethodwhich
mąkę themagnetronworkinginternallyatthesame
workingpointtochangetheoutputofthemagnetron.
Thismethodwascalled "CONDUCTION RATIO
CONTROL".Butthereisanothermethodwhichis
called"ELECTRICLEVELCONTROL"whichis
throughchangingtheworkingpoint(suchasanodę
voltageormagnetic field) tochangetheoutputofthe
Fig
2-6
magnetron.Becauseofconductionratiocontrol
methodisIowcost,highfunctionandhigh reliability, itiswidelyusedforthose microwave ovenwhichhavethe
doorreleasebutton
Fig. 2-5(b)
timer& powermotor
l
220V
transformer
6

powercontrol function.
FIG.3-1 isthepowercontrolcircuitdiagramofbrandmicrowaveoven,WP700.Thisisa typicalinstanceof
conduction ratiocontrol.Thisovenadopt time andpowercontrollerasa whole. Whena 220V,50Hzalternating
currentis inputted, thetimeandpowermotorisalwaysatworkingcondition.Atthe FIG.2-7, S5isalways
conducted. Madę theS5working30secondsasa circle,theconducttimecanbesuccessivelyadjusted from 5
secondsto30seconds.Whenpowerselectswitchissetat "HIGH", S5isalways conducted, theoutputofthe
microwaveovenis 700W(full power)whenthepowerselectswitchissetatdefrostposition,S5 would conductfor
14.4seconds,andcut off for 15.5 seconds, andtheaverageoutputoftheovenis336W.
2.4.3THERMAL CUTOUT
Thermalcutoutactuallyisa thermalsensorswitch,usually,itisfixedonthe shell ofthemagnetron,andseries
connected with the primary circuitofthemagnetrontocontrolthepowerinput.At normal condition,thethermal
cutoutisalwaysconducted (FIG.2-8). Whensomethingwrongwiththecoolingsystemthatcausesomeabnormal
conditions,suchasmoldingorthermalbreakdown, which madę thetemperaturęofthemagnetronreachthelimit
value.Then,thethermalcutoutwouldworktoturnoffthepowertopreventthemagnetronfrom being damaged.
2.4.4HEATING CHAMBER
Heatingchamberistheplacewherethemicrowaveandthefood affect mutually. There arę lots kinds ofchamber.
Accord-ingtotheworkingcharacters,itcanbeclassifiedto carton type,cavitytype,radiationtype, słów type
(surface wavetype),etc.Thepresentadoptchamberforfood cooking microwaveovenisthetypicalcartontype
heating.(FIG.2-8).Theheatingchamberismainlycomposedofovendoorandovencavity.Fromthemicrowave
theory, itisa microwaveresonantcavitythatcancontain many kindsofoscillatingmodels simultaneously.
Microwaveentersintotheoven cavity throughthewave guide andthecoupling appliance, andmostofitsenergy
isabsorbedbythefood after itisreflectedinthe cavity repeatedly, thosewhich haven't beenabsorbedwillbe
reflecttothemagnetron.A gooddesignedovencavityshouldhavea goodimpedancematchingwiththe
magnetron,theenergyshouldbelessreflect,anddistributeevenlyintheovencavity,improvetheheating
efficiency. Generally,atthesameinputpower,thelargerthecavity,thelesstheenergydensitya unitvolume
would have intheoven,andthe morę energyontheinside wali ofthecavitywould lose, thence,itwould certainly
słów downtheheatingspeed,Iowtheheatingefficiency. Moreover, toobigofthe cavity wouldeitherwastethe
materiałorappears very heavy.Themateriałfor cavity usuallyusenon- magneticstainless steel orzinc- plating
steel, andhavenohighrequirementsfortheconducting ratę. Theinside coating ofthecavity reguires beautifulin
look, durablewhenuse(shouldberesistantagainst damp, heat,acidandalkali),itshould also complywiththe
foodhealthrequirements.
1. Safetyinterlockswitch
2.Door window
3.Airvent
4.Roller Shaft
5.Turntable supporter
6. Glass tray
7.controlpanel
Toimprovetheheatingevennessthere often fixeda turntable glass trayatthebottomofthe cavity (FIG.2-8).Itis
throughchangingtherelativeplaceofthemicrowaveandtheheating matter toimprovetheheatingevenness.
Theturntabletrayisusually madę ofheat- resistant glass, theglasscontainssomedielectric loss, itcan,
somewhat,protectthemagnetronwhenthecavityloadingless.
Thereoftenfixeda dust- proof, Iow- lossandheat- resistantdielectriccover(suchas mica sheet). Sometimes,
animpedancematchingmetalstickwasfixednearthecouplingorinthewaveguide.
Thedoorisdesignedfor inspecting, takingand placing theheatingfood,itisalsoonesideofthecavity(FIG.2-
l

current-resi stant
constructure
8).Itisthemostliableplacewheremicrowaveleakageoccurs.Especially,aftera longtime using, themicrowave
leakage would enlargeatthehingeandthehook. Anyway, mechanicdamage would also cause large amountof
microwaveleakage. Therefore, themainmethodsdesignedforpreventingmicrowaveleakageofthedoor arę as
follows:
1) Assemblea layerof steel filamentora thinmetalpiątewithmanyholesatthemiddleofthewindowto madę it
ispossibleto observe theheatingas well asshieldingthemicrowave.
2)Thewidelyused seal measurementatpresent
istoassemblea current- resistantconstruct
between thedoorandthe doorframe. FIG.2-9 is
thetypicalconstructionfigofthedoor.Itwas
designedaccordingtothetheoryof
"THETRANSFERING LINĘ ONE-FOURTHWAYE
LENGTHIMPEDANCE CHANGER". Although
thereisnoconnectingpoint from a mechanical
point.Itissealedatthe seam fromthepointof
electricity, soitiscalled "CURRENT-RESISTANT".
Recently,withtheinstallationofnoisefilterinthe
currentresistanttrough,the effect torestrainthe
microwaveleakage(includehighsubharmonic) - Pig 2-9
havebeenmuch improved.
frontdoorpiątenoisefilter
ovendoor
3TYPICALCIRCUITANALYASISOF MICROWAYE OVEN
Wehaveintroducedthestructureandtheworkingprincipleofthemicrowaveovenpreviously.We shall analyze
thecompletesetcircuitofthemicrowaveoven link withthepracticalcircuitatthischapter.
SCHEMATICDIAGRA
Unii \snot operated
Fig. 4-1
Fig.3-1 isthepracticalcircuitdiagramofa brandmicrowaveoven. Its correspondingworkingconditions arę as
follows:Thedoorclosed,SW1andSW2turnedon,SW3closed,powercontrol relay hasnopower, R1, R2iscut
8

off.Whencooking,touchthestartingswitchtopowerthetimerandthepowerrelay. RY1, RY2closedthepower
supplytotheanodęofthemagnetronandthefilament,changingthepowerfrequencyelectricenergyto
microwaveenergy,themicrowaveenergythentransferredtotheheatingchamberforfoodheating.Atthesame
time, thelampturnedon,thefanmotorbeginsto cool themagnetron.Theturntablemotorsetofftodrivethefood
aroundandmakingthefoodheatedevenly.Themicrocomputerbeginsreckonthetime,whenitreachedthesets
time, powerrelay arę cut off, thepowerofthelamp, all themotorandthemagnetron arę cutoff,thefood-
heatingprocessended.Duringtheheating,ifthedoorwasopened,theinterlock S1, S2willcutoff,S3will close,
allthemotorsandthemagnetronwill also becutoff,thelampwillturnon,theovenstopheatingimmediately.If
heatingneedgoon, just pushdownthestartingbuttonandclosedthedoor,theovenwillcontinueitsworking.
Whensomethingwrongwiththefanmotorortheairventwasblockedthatbreakdownthecoolingsystem,the
magnetrontemperaturę would risehigh very quickly.Whenthetemperaturęreachedtheworkingpointofthe
thermalcutout(S6),S6willbecutoffimmediatelytocutoffthepowersupplytothemagnetronandthe
magnetronwillstopsworkingrightaway.ThePCboardiscutofftopreventthemagnetronfrombeingdamaged
byoverheating.Whenthethermalcutoutiscutoff,themagnetron,motorsandthelampwouldstopworking
simultaneously.Moreover,thethermalcutouthasthe self - resumingcharacter,whenthetemperaturęIowered,it
willresumetoclosecondition.
Circuitdiagramofcomputercontrolledmicrowaveovens:
Circuitdiagramformechanicalcontrolledmicrowaveovens:
4 HOW TO ASSEMBLE AND DISASSEMBLE MICROWAVE OVEN
COMPONENTS
Inthefollowingpages,wewillintroducethewaysin which thevarious parts ofa typicalmicrowaveovencanbe
disassembledandassembled.
4.1THEGABINET
Todisassemblethecabinet
Puli outthepower pług.
Loosenthefourscrewsatthebackoftheovenwitha "+"- screwdriver. (FIG.4-1 a)
Pushthecabinetback25mmaccordingtothearrowdirectionshownat FIG.4-1 (b),andthecabinetcanbetaken
off.
(a)
Fig. 4-1
Toassemblethecabinet
1. Putthecabinetontheoven,andpushit fuli ahead.
2.Checkwhethertheup,rightand left troughshavebeen inserted withthe curved withthe curved rimofthe
oven(FIG.4-1 (b)). Ifthecabinetandtheoven arę nottalliedexactly,thenitshouldbereassembledorthose
untalliedpartsshouldbesmoothed.

3.Tightenthosefourscrews,please mąkę surę thatoneofthescrewsshouldhavea plumblossom shape
washertokeepa good earth.
4.2THE DOOR COMBENATION
Todisassemble,
1. Puli outthepower pług.
2.Take off thecabinet.
3.Loosenthe two six -angle screwsof left hinge(up)
witha socketwrench(FIG.4- 2).
4.Pushthedoorreleasebuttontohavethehookout
(FIG.4-3).
5. Puli thehingewiththedooroutoftheoven
together,andtakeoffthewasherofthehinge(Iow)
shaft (FIG.4- 2).
6.Pickuptheteninversehookswhicharoundthe
coverwitha smaliscrewdriver
carefully(ATTENTION:thecoveris madę of
plastics,andis very liabletobebroken),andtake
outthecover.
7.Takeoffthetwoscrewsatthedoorside
witha "+"-screwdriver
8.Takeoffthehinge(up)(FIG.4-2).
9. Apart the doorframe from thedoorplate
(FIG.4-2).
dc
10.Takeoffthehookspringwitha pointed
plier, thenthehookcombination.
11. Clamp thewindowpiątewithhand,pushit
downaccordingtothearrow direction,
andtakeitoff.
six~angle screw
hinge(up)
oven
Fig. 4-2
l atch swtch holder
pilot swtch
l atchswtch hol der
l atchswtch
l otswtch
(b)
Toassemblethedoorcombination(seesketch
4-2 to 4-5)Fig. 4-3
1. Apply propersilicongreaseorlubricating
greaseonthe "*" mark ofthehook first, thenfixthehookontheovendoor,andthespringonitsplace
(FIG.4- 5),checkwhetherthehookisoperatinginnormal.
2.Applypropersilicongreaseorlubricatinggreaseonthe "*" markofthehinge(UP),installthehinge(UP)in
theholeatrightaboveofthedoorasFIG.4- 2, theninstallthewindowonthedoorasFIG.4 -1, mąkę surę
thehookwon'tout.Thentighteneachhookonthewindowtothetroughofthedoor. After assembled,check
whetherthedoorhookisworkinginnormal.
Fig. 4-4
Fig. 4-5
10

3.Tearoffthebackprotectivepaperofthe window, thenthesidesofadhesivetapeasFIG.4- 1, andstickiton
thewindow,Tearthreerightsidesprotectivepaperabout10mm,andfixthewindowinthe doorframe as
FIG.4-1.
4.TearofftheadhesiveprotectivepaperoftheliningandstickitonthedoorasFIG.4- 1, slipthehookonthe
doorframe,andfixthedoorframeonthedoor,tightenitwith "+" - screws. After assembled,check whether
thehookworkinginnormalandwhetherthehinge(UP)isitsposition.
5.AccordingtotheFIG.4 -4 shown, pastętheinnerlininginsidethe doorframe, mąkę surę itispasted
smoothly,andshouldhavenoair bubble.
6.Slipthewasherinthehinge shaft, then put thehinge shaft inthehingeholeonthebottomoftheoven,the
hingeintherectangleholeonthe left above,andhookeditwiththedoorhook.
7.Placea 0.15mm thinpaperbetweenthedoorandtheoven,levelthedoorandtheoven,thenpushthedoor
close totheoven,andtightenthe two screwsofthehinge(UP)andpaintthem.
4.3THE CONTROL PANELANDTHE DOOR RELEASE WECHANISM.
Puli outthepower pług.
Takeoffthecabinet.
Dischargebetweenoneendofthecapacitorandthebaseboardwitha
screwdriver.
To disassemble
1. Puli outtheterminal pług ofthetimeandpowerdistributor.
2.Takeoffthescrewwhichfixthecontrolpanelwitha "+" - screwdriver
(FIG.4- 6)
3.Takeoffthecontrolpanel.
Toassemble,
(1)Placethetwobucklesunderthecontrolpanelintothetworectangle
holes undertheovenasFIG.4- 6,then mąkę closeofthecontrolpaneland
theovenwithbeingfixedwitha screw. Pług intheterminal pług.
Fig.4-6
4.4THE MAGNETRON.
Firstly,doas 1,2,3, stepsatIIIofthis part.
To disassemble,
1. Takeoffthescrewbesidetheovenlamp(FIG.4- 8).
2.Takeoutthefourscrewswhichfixedthemagnetron,andtakethemagnetronoff(FIG.4- 7).
magnetron
screwe
thermal cutout
magnetronholder magnetron holder
lampshade
Fig. 4-7
Toassemblethemagnetron,
1.Checkwhetherthecopperfilamentweavedwasherofthemagnetronantennahasbeenplaced well. It
shouldnotbefixedifthereisnocopperfilamentweavedwasher,forit may causethemagnetronandthe
ovencan't earth well,andcause large amountofmicrowaveleakage.Attention: Whena newovenmatches
11

amagnetron,the meatl lustreat "*" mark should bepolishedwitha sandpaper(FIG.4-7).
2. Aim the head ofthemagnetronantennatotheholeofthewave guide housing,tightenthefourscrewsofthe
magnetron vertically, and also tightenthescrewsofthelampshade(FIG.4- 8).
3. Pług inthe two terminalsofthemagnetronfilamentandthethermalcutout.
4.5THE TRANSFORMER.
Firstly,doasthe1,2,3,stepsatIIIofthis part.
Dismantlingstepsforthetransformer:(asFIG.4-9).
1. Puli out all theterminalofthetransformer.
2.Turnthemicrowaveover.
3.Take off therightbaseboardwiththetransformer after loosenedthefour screws, whichfixtheboardonthe
oven. (4-10).
Takeoffthefourscrews,a,b, c, d with a"+"- screwdriver. 4.
5.Takeofftherightbaseboard,theseatandtherubberspace between thetransformerandtheoven.
baseboard
transformer
Fig.4-10
Fig. 4-9
tomountthetransformer,
1.PlacethetransformerastheFIG.4- 9,tearofftheprotectivepaperoftherubberliningtape,stickitonthe
transformerasshownonthefigurę.Thenputontheseatandtherightbaseboard, mąkę surę thescrew
hole arę tallied,thentightenthefourscrewsforthehighvoltagewindingis earthing here.
2.Fixthetransformerontheovenas FIG.4-10.tear offtheprotectpaperoftherubber spacer, setitbetweenthe
transformerandtheoven, mąkę surę theadhesivesideisstickedontheoven.
3. Pług inalltheterminalsofthetransformerprecisely.
4.6 THEFAN MOTOR.
Firstly,doasthe1,2,3,stepsofIIIofthispart.
To disassemble,
1. Puli outthetwoterminalofthefanmotor(FIG. 4-11).
2.AccordingtotheFIG.4-12, puli outthe lead pług which
marked"A"and"C"fromthethermalcutoutandthefuse
housingseparately,andtakeofftheearthingscrewwhich
marked"B" (FIG.4-12).
3.Takeoutthepowersupplycordfromthetroughasthe
figuręshows.
4.LoosenthescrewsshownontheFIG.4-13witha "+" -
screwdriver,andtakeoffthefanholder.
/ YU
/power supplycord
Fig.4-11
12

5.Take off thefanfromthefanmotor shaft asFIG.4-14,thenthefan motor,
to mount thefanmotor,
1.AssemblethefanmotorasFIG.4- 14.Dripthe glue on
the "* " placeofthefanmotorshaft,and f ixthefanonthe
motor, mąkę surę it must befixedtothebottomofthe
shaft.Attention:Thefanmotorshaftshouldnotbe curved,
thefanshouldhavenoabnormalstickup. After assembled,
checkwhethertherunningfan would knockthefanholder.
2.AssemblethefanholderasFIG.4- 13,Thenconnectthe
powersupplycordwiththe two wiresofthefan motor, and
tightenthescrewsasFIG.4- 11 andFIG.4- 12.
screw
earthingscrew
Fig.4-12
fan motor ^ack
b^ard
Fig.4-14
Fig.4-13
4.7 THE CAPACITOR.
Firstly,doasthe 1,2,3, stepsofIIIofthis part.
Todisassemble,
1. Puli thewiresofthecapacitorout (4-15).
2.Loosenandtakeoutthescrewwhichfixthecapacitor clip
witha "+" - screwdriver, andtakeouttheclipandthe
capacitor.(4-15).
Toassemble,
1.Placethecapacitor in thecapacitorclipwiththeendwhich
havethreefootnearthediodę (4-16).
2. Insert oneendoftheclipinthefanholdertrough (FIG.4-15).
3.Tightenthescrew,whichfixthecapacitorclip.
4. Pług in all the plugs ofthecapacitor.
capacitox
fanholder
Fig.4-15
4.8THEDIODĘ.
Firstly, doasthe 1, 2,3,stepsofIIIofthispart.
Todisassemble,
1. Puli outthediodę pług, whichpluggedinthe
capacitor.
2.Loosenthe screw, whichfixedthediodę,and
magnetron
capacitor
transformer
Fig.4-16

takethediodę off.
Toassemble,
1. Insert oneendofthediodętoonefeetofthecapacitor'sconnectpiece.
2.Fixthediodęwithonescrew(payattentiontothepolarityofthediodę,refertoFIG.4 -16).
4.9THETURNTABLE COMBINATIOM.
Firstly, doasthe 1,2,3, stopsofIIIof this part.
Todisassemble,
1.Turnthemicrowaveovenover(FIG. 4-17).
2.Takeoffthe two screws which fixthemiddlebaseboardwitha
"+" - screwdriverandtakeoffthemiddlecover(FIG.4 -18).
3.Loosenoutthetwoscrewsofturntablemotorwitha "+"-
screwdriver,takeouttheturntablemotorand puli outthetwo
wires(4-17).
Assemblingsteps:
1.Putthemotor shaft intoitsconnecting hole, andfixthemotor
withtwoscrews(FIG.4 -17).
2. Pług inthetwowires.
3.Assembleandfixthemiddlebaseboardwithtwoscrews
(FIG.4-18).
4.Turntheovenback.
5.AstheFIG.4- 19shown,fixintheturntableshaft supporter,
theplaceintherollerringandthe glass trayasFIG.4- 20.
Fig.4-17
Fig.4-18
turntableshaftsupporter
rollerring
Fig.4-19
©©
o©
& <s>
©s©
4.10THEDOOR SAFTY INTERLOCKS.
Firstly,doasthesamewith1, 2, 3,stepsofIIIofthispart.
Stepsfordismantling:
(1) Puli outtheterminal plugs oftheinterlockswitchandthepilotswitch.
(2)Loosenoutthetwoscrewswhichfixedtheswitchholderwitha "+"- screwdriver, andtaketheswitch holder
off.
(3)Takeofftheinterlockswitchandthepilotswitch from theholder.
(4)Takeofftheswitchconnectinglever arm andtheworkingleverfromtheholder.
Assemblingsteps:
14

latch switch hołd
rontdoor pl
(1) Slip ontheconnectinglever arm andtheworkingleverintotheswitchholder.
(2)Assembletheinterlockswitchandpilotswitchtotheswitchholder, mąkę surę they arę assembledcorrectly.
(3) Tightly fixtheholderwith two screws.
(4)Checkthepositionofthehookandtheswitchholder.
screw
Close thedoor,pushand puli theIowandup part ofthe
doortocheckwhetherthedoorisflexible. If itdoes,back
andfrontpositionoftheholdershouldbeadjusted.
Providedtheuphookis loose, thedoorshouldbepushed
morę closelytothe oven, and puli theholderinsideclosely
after loosenthescrew which fixthe holder, then,tightenthe
screwandcheckwhetheritis still loose.Ifitisnotorthe
looseisminor,it would beOK.Openthedoor,then close it
lightly, checkwhetherthehookisinposition,ifnot,
readjustmentisneeded.Ifthelooseisat Iower partofthe
door,theadjustmethodsisthesamewiththeabovesaid
stepsbutthescrewistheone below (FIG.4- 21).
4.11 THE CONTROL PANELOF A TYPICAL WICROWAYE OVEN
Puli outthepower pług.
Takeoffthe cabinet.
Discharge between oneendofthecapacitorandthe
lighttoughswitch
controlpanel
Fig.4-22
lighttoughswitch
controlpanel
baseboardwitha screwdriver.
MeansofdismantlingthePCboardanddoorrelease
mechanism:
(1) Puli out all theterminal pług ofthePCboard.
(2)Loosenoutthetwoscrewswhichfixthecontrolpanel
witha "+"- screwdriver(FIG.4-6).
(3)Takeoffthecontrolpanel.
(4)Takeoffthethree "+"- screwswhichfixthePCboard
astheFIG.4- 22.
(5)Takeofftherangęterminal plugs asFIG.4- 24shown,
thatispressthetwoplacesaccordingtothearrow
directionatthefigurę, while puli itupabout2mm,thenoff
the rów plasticboard.
(6)TakeoffthePCframe.
(7)Tearofftheundriedglueofthelighttouchswitch(FIG.4
-23).
toassemblethePCboardanddoorreleasemechanism,
(1) Tearofftheundriedgluepatchofthelighttoughswitch
(1)and(2)asthe Fig.shown, andplacethemintothe
rectangleholeofthe surface oftheplasticboard.
(2)Afteruprightedthelighttoughswitch,tearoffthe
protectivepaperontheback,andstickitontheplastic
boardsmoothly.
(3)Tearofftheprotectivepaperofthelighttouchswitch(2),andsticktheswitchonthebackoftheplasticboard
smoothly.
(4)AssembleinthePCframeandPCboardasFIG.4 -22,
andfixthemwiththree "+"- screwes.
(5)Fixtherangęwiresas FIG.4-24, themeans arę: Insert
therangęwiresfirst, mąkę surę thatitsnotchistalliedwith
theflangeofthe rów seat,then,pressitdowntoitsnormal
15
Fig.4-23
Fig.4-24

position.
(6)Fixthecontrolpanelontheoven (FIG.4-6).
(7) Pług intheterminal plugs ofthePCboard.
5 BREAKDOWN ANALYSIS ANDTHE MEANS OF OVERHAULIHG
Beforeoverhaulinga microwave oven, youshouldjudgethebreakdownandthecause correctly, thenyoucan
repairitwithcorrespondingways.Theoverhauling must beproceedinorder,anyhasty conclusion isnot
recommendable, otherwise over-working would bedonewhenrepair.Themicrowaveovenmayoccur compound
breakdowndueto all kindsof different reasons, thus,whenoverhaul,they all shouldbetakenintoconsideration.
Specialattentionmustbegiventothemicrowaveleakageandtheelectricinsulationwhenexaminebecausethey
maydoharmfultotherepairing staff.
5.1 EXANHNING THEBREAKDOWNCAUSES.
Howtoexaminea microwaveovenwithbreakdown?A better means which demonstratedinpracticaloperating
arę throughinspectingandlistening.Onthebasisof large amountsofperceptual knowledge, youcanjudgeand
analysiethebreakdownquicklyandcorrectly.
5.1.1INSPECTION.
Inspectwhethertheovenshapeisdisorderedandwhereisthedisordered position, If any.Itisnormalifthe
cabinetdisordereda little, butabnormaliftheoven,thedoordisordered,thedoorhookbroken,thedoorcrooked,
orthere arę toomuchlooseness between thedoorandtheoven after thedoorisclosed.
5.1.2LISTENING.
Listeningtothesoundoftheovenoperatingandthenoiseofthefan.Minor"wenwen"noise, cycling"kala"noise
and "shishi" noiseshouldbeconsideredasnormal.Butitisabnormalifthefollowingnoisesoccur:
(1)Sound"wenwen " noise.
(2)Longtime"shishi"noise.
(3)Strikesound like "Pipapipa"
5.2SPOT EXAMINING STEPSOFTHE MICROWAVE
OVEN
5.2.1 EKAMINE THE MICROWAVE INSULATING RESISTANCE
Measure theinsulatingresistancewitha avometerora
megaohmmeterthevalueshouldnotbelessthan2 megaohms.
Otherwise, part examinationshouldbetakenatonce.Suchas
checkingwhetherthemotor,thethermalcutout,thetransformeror
thecapacitor arę electricity leaking.
5.2.2 EXAMINATION OFTHERESISTANCEVALUEOFTHE
MICROWAYE OVEN.
Close thedoor,setthetime(theovenisatoperatingconditionbut
thepower pług haven'tbeenpluggedin),measurethe two feet(L-
N)ofthepower pług with Rxi gradeofanavometer,theresistancevalueshouldbeabout2.5 ohm. Ifopencircuit
occurs,thenyoumustcheckwhetherthe8Afuseis broken> the primary windingofthetransformerisopen
circuit > thethermalcutoutisopencircuitor not, youmustcheckwhethertheinterlockdeviceisputthroughorall
theplugs arę connected well. If short circuitoccurredorthe
resistancelessthan1.5 ohms, youshouldcheckwhetherthe
primarywindingofthepowertransformerisshort- circuitedorpart
short-circuited.
5.2.3 EXAMINATION OF MICROWAVE LEAKAGE.
Measurethemicrowaveleakagewitha microwaveleakagemeasure.
16
Fig. 5-1

primary winding
transformer
Placea graduateof275mlwateratthemiddleofthe glass tray
oftheoven(FIG.5- 1). Close thedoor,powersethigh, time set
to3 minutes, pressthe starting button tooperatetheoven. After
rectifiedthemicrowaveleakage measure, measurearoundthe
doorcrack,thoseholepositionofthewindowandtheairventat
foursidesoftheovenwiththepróbęofthemeasure.When
measure, themovingspeedofthepróbęshouldnotexceed
25mmpersecond,andthemeasuringdirectionshouldbethe
samewiththeoutingdirectionofthepróbęshouldnotexceed
25mmpersecond,andthemeasuringdirectionshouldbethe
samewiththeoutingdirectionofthe microwave leakage(FIG.5-
2)..
Whenmeasuringtheultimatevalueofmicrowaveleakageofallthemeasurepositionshouldnotexceed1
milliwatt/cm2, ofshouldbeconsideredasabnormal.
5.2.4 EXAMINE WHENTHEOVENAT OPERATING, BUTTHEFOOD CANT BEHEATED.
(1)Examinewhenthelampison,theglasstrayiscycling,the
Fig. 5-3
fanoperating in normal:
Take off thecabinet,startingtheoven,measurethe pług ofthe
transformerwithanavometertoseewhetheritisenoughto
220V. If itisenoughto220V,thenthe secondary highvoltageof
thetransformershouldbeexaminedasFIG.5- 3.
Measureitwiththe2500V-alternatinggradeofmodel500
avometer.Onerodoftheavometerconnectstheiron córę ofthe
transformer,theotherrodconnectsthesecondaryhighvoltage
pług (FIG.5- 4).Theavometerreadingshouldbeabout 2100V
(whenmeasure,becarefulwiththehighvoltage).Ifnovoltage
atall,itindicatesthatthetransformerhasbroken,andshouldbe
replacedbya newone.Ifitisenoughto 2100V, thencheckthe
filamentvoltageofthetransformerwithalternating 10V gradeof
an avometer, thevalueshouldbeabout3.4V(FIG.5- 5).
Ifthereisnovoltageatall,itindicatesthetransformerhas
broken,andshouldbereplacedbya newone.Ifitisenoughto
3.4V,checkthefilamentresistanceofthemagnetron,measure
thefilament pług withthe R*1 gradeofa avometer(FIG.5- 6).If
itisopen- circuited, itindicatesthemagnetronhasbroken,and
shouldbereplacedbya newone.Itisnormaliftheresistance
very smali.Thencheckwhetherthemagnetron steel hasbroken,
ifbroken,replacewitha newmagnetron.
Ifthereisnoproblemwiththe magnetron, checkthehigh
voltagediodęthen.Measurethediodęwith RxiOK gradeofan
avometer,the "+" rodendoftheavometerconnectthecathode
ofthediodę,the "-" rodendoftheavometerconnecttheanodę
of thediodę (FIG.5-7).
Theavometerreadingshouldbeabout150thousandohms.
Thechangetherodto different electrode,thereadingshouldbe
"°°" . Ifthereadingis very smali,andnearto short circuit, it
indicatesthehighvoltagediodęhasbeenpunctured,and
shouldbereplacedbya newone.
Ifthehighvoltagediodęis OK, thencheckthe forwarding pług
ofthetransformertoseewhetheritisenoughto220V.Ifitisnot
enough,checkthe micro - switchofthetimeandpower
distributor.Connectthetworodsoftheavometertothe1,2place
ofthetimerwith RxiK grade.Itisnormalifthereadingis"O"
whenatcutoffcondition.Ifthereadingis "°°" , itindicatesthe
11
transformer
secondarywinding
Fig.5-4
filament wingding
Fig.5-5
magnetron

micro switch has broken,andthe timer shouldbereplacedbya newone.If all theaboveexaminationshows
normal ,then checkwhethertheterminal pług ofthemagnetronandthecapacitorhaveloosened,ifitisloosened,
pinchittightlywitha pliers.
5.2.5 EXAMINE THE STARTING ANDTHE8A FUSE OF
THE MICROWAVE OVEN.
Puli outthepower pług, take off thecabinet,dischargethe
capacitor, measuretheresistancevalueofthe primary
windingandthesecondarywindingofthetransformerwithan
avometer(FIG.5- 10andFIG.5- 9).Theresistancevalueof
theprimarywindingshouldbeabout2.2ohms,thesecondary
windingshouldbeabout 130 ohms. Otherwise, itindicatesthe
transformerhasbroken,andshouldbereplacedbya new
one.
Ifthetransformerisnormal,thenthehighvoltagecapacitorFig.5-8
shouldbechecked. Puli outtheconnecting pług ofthe
capacitor, andmeasureitwith R*1 gradeofanavometer,the
tworodsoftheavometerconnectthetwopolarityofthecapacitor.Whentheyjustconnected,thereadingofthe
avometershouldbezero,thenincreasestoninemegaohm
slowly.Changetherodto different polarity,thereadingrepeat
fromzerotoninemegaohm(FIG.5- 11),itmeansthe
capacitorisnormal.Ifthe indicator oftheavometercan'tpoint
outfromzerotoninemegaohms,itindicatesthehighvoltage
capacitorhasbroken,andshouldbereplacedbya newone.
Ifitisnormal between thetwopoleofthecapacitor,thenthe
insulationbetweenthecapacitorpoleandthecabinetshould
bemeasuredwith RxlOK gradeofanavometer.The
resistancevalueshouldbe "°°" (FIG.5- 12).Ifitis short
circuitedorhavea numberreading,itindicatesthatthe
capacitorhasbeenpuncturedorelectricityleaked,andshould
bereplacedbya samemodel,samecapacityone.
secondarywinding
Fig.5-9
transformer
primarywinding
Fig.5-10Fig.5-12
magnetron
Iftheresistancevalueofthecapacitor'stwopole arę "°°" , thecapacitorisnormal.Thencheckthe earth ofthe
magnetron'stwofilamentstoseewhetherthey arę short-
circuited(FIG.5- 13).Ifthey arę short- circuitedandthe
filamentstrikesthe shell ofthemagnetron,itindicatesthe
magnetronhasbroken,andshouldbereplacedbya new,
samemodelone.
Ifthemagnetronis also normal, thentestthepilotswitch.
Puli outthetwo plugs oftheswitch.Measureitwiththe R*1
gradeofavometer,thetworodconnectthe pług ofthe
switch, theresistancevalueshould be"°°" (FIG.5- 8).
Thenpressdownthepilotswitchwitha screwdriver,ifthe
readingoftheavometerpointedtozero,itindicatesthepilot
switchhasbroken,andshouldreplaceitwitha new,same
18
Fig.5-13

modelone.
5.3 REPA1RING METHOD OF SEYERAL BREAKDOWN
1.Repairwhenthereoccurred large amountsmicrowave
leakage.There arę manyfactorswhichmaycausemicrowave
leaking. Followingmentionedmaybethe main causesof
microwaveleakage:
(1)Thedoordeformed,thehingeloosedordamagedthat
causedthedoorcannot close tightly.
(2)Thedoorpressingcoverorthe embed piecedamagedor
come off.
(3)Obviousdamageorunevenoftheoven.
(4)There arę filth betweenthedoorandtheoven.
(5)Thedoorandtheoven arę serious loosed after thedoor
closed.
doorhinge(up)
doorhinge (Iow)
Fig.5-14
(6)Thecrackofthedoorshieldingnetcover.
Before repairing, checkwhethertheabovelistedpoint arę
existed, ifnot,canyoustartthemicrowaveoven.Placea graduateofabout275mlwateratthemiddleofthe
glass tray,closethe door, time setat3 minutes,powerathigh, mąkę theovenoperatinginnormal. Rectify the
microwaveleakagemeasure,measuretheamountofthemicrowaveleakagearoundtheovenwithitspróbę.If
there arę placeswhichtheleakageexceedsthestandardrequirement,thenrepairthemaccordingly.Ifthe
leakageamountexceeds1 milliwatt/cm2 atthe left doorcrack,
then puli outthepower pług, takedownthecabinet,adjustthe
screwsofthehinge(upandIow)as figure5-14 tolessthegap
betweenthedoorandtheoven.Thenmeasureagain,the
leakageamountshouldbelessthan1 milliwatt/cm2. Generally,
itshouldbecontrolled below 0.75 milliwatt/cm2 withsome
allowance.
Iftheleakageoccurredattherightdoorcrack,adjustthe
screwswhich fix theinterlockholderandthehook.Ifthe
leakageisthelargersideattheright- aboveoftheoven,then
adjusttheupperscrewasFIG.5- 15.Loosenoutthescrew,
pushthedoorclosetotheoventohookthedoorhookwiththe
plastic parts, thentightentheScrewagain.Iftheleakageis
largerattheright- below,thenadjustthe Iower screwasFIG.5
door pushing,
part at —
right above
doorpushing,
part at —
rightbelow
screw
micro switch
screw
Fig.5-15
-15.Loosenthescrew,pushthedoorclosetotheoventohookthedoorhookwiththeswitchholdertightly,then
tightenthescrewagain,andopenandclosethedoorrepeatedly,tocheckwhetherthedoorcanoperateflexibly,
whetherthehookandtheswitch arę intheirnormalposition.Ifitisnotin position, thenadjustthedoorhookand
theswitchholderrepeatedlyto mąkę themtonormalposition,toputthroughtheinterlocks,tocutoffthepilot
switch,tolesstheloosebetweenthedoorandtheoven,thenmeasuretheleakagewithmicrowavemeasure
again.
Iftheleakage still exceedsstandardrequirement,theninspectwhethertherightovenisevenornot,ifnot,
smooth it.Thenadjustthedoorandtheovento eliminate theirloosetotheultimate.
Iftherestillexistmicrowave leakage, measurenearthe
magnetronwiththepróbęofthemicrowaveleakage mea-sure. If
theleakageislarger,theovenshouldbeturnedoffandcheck
whetherthefourscrewswhichfixthemagnetronhavebeen
loosed,ifloosed, twist themtightlywithsocketwrench.Ifthefour
screws arę fixed,thenthemagnetronshouldbetakendownto
checkthecopperfilamentweavedwasherofthemagnetronhas
beenplaced well orwhetherthewaveguidehousingcoupling
hasbeen oxidized orhave lacguer onit.Ifdohave,scrapethe
oxidized layer orthe lacguer off.Whenfixthemagnetron,the
19