Dacor DMT2420B User manual

DMT2420B
DMT2420R
DMT2420S
Intheinterestofuser-safetytheovenshouldberestoredtoitsoriginalconditionandonlypartsidenticaltothosespecifiedshould
be used.
WARNING TO SERVICE PERSONNEL: Microwave ovens contain circuitry capable of producing very high voltage
and current. Contact with the following parts may result in a severe, possibly fatal, electrical shock. (Inverter unit
that includes High Voltage Capacitor, High Voltage Power Transformer, High Voltage Rectifier and Heat sink etc.,
and Magnetron, High Voltage Harness etc..)
TABLE OF CONTENTS Page
PRECAUTIONSTOBEOBSERVEDBEFOREANDDURINGSERVICINGTO
AVOID POSSIBLE EXPOSURE TO EXCESSIVE MICROWAVE ENERGY ................... INSIDEFRONTCOVER
BEFORESERVICING ...................................................................................................... INSIDEFRONTCOVER
WARNINGTOSERVICEPERSONNEL ................................................................................................................1
MICROWAVEMEASUREMENTPROCEDURE.....................................................................................................2
FOREWORDANDWARNING................................................................................................................................3
PRODUCTSPECIFICATIONS...............................................................................................................................4
GENERAL INFORMATION ...................................................................................................................................5
OPERATION .........................................................................................................................................................6
TROUBLESHOOTINGGUIDE .............................................................................................................................10
TESTPROCEDURE ............................................................................................................................................11
TOUCHCONTROLPANELASSEMBLY .............................................................................................................26
COMPONENTREPLACEMENTANDADJUSTMENTPROCEDURE ..................................................................27
PICTORIALDIAGRAM ........................................................................................................................................33
POWERUNITCIRCUIT.......................................................................................................................................34
LSIUNITCIRCUIT...............................................................................................................................................35
PRINTEDWIRINGBOARD .................................................................................................................................36
PARTS LIST........................................................................................................................................................37
PACKINGANDACCESSORIES .........................................................................................................................41
S12M201DMT24E
DMT2420B
DMT2420R
DMT2420S
MICROWAVEOVEN
MODELS
SERVICE MANUAL
This document has been published to be used for after
sales service only.
The contents are subject to change without notice.
dis tinctive appliances

DMT2420B
DMT2420R
DMT2420S
PRECAUTIONS TO BE OBSERVED BEFORE AND
DURING SERVICING TO AVOID POSSIBLE
EXPOSURE TO EXCESSIVE MICROWAVE ENERGY
(a) Do not operate or allow the oven to be operated with the door open.
(b) Makethefollowingsafetychecksonallovenstobeservicedbeforeactivatingthemagnetronorothermicrowave
source, and make repairs as necessary: (1) interlock operation, (2) proper door closing, (3) seal and sealing
surfaces (arcing, wear, and other damage), (4) damage to or loosening of hinges and latches, (5) evidence of
dropping or abuse.
(c) Before turning on microwave power for any service test or inspection within the microwave generating
compartments,check themagnetron,waveguideor transmissionline, andcavityforproperalignment, integrity,
and connections.
(d) Any defective or misadjusted components in the interlock, monitor, door seal, and microwave generation and
transmissionsystemsshallberepaired,replaced,oradjustedbyproceduresdescribedinthismanualbeforethe
oven is released to the owner.
(e) A microwave leakage check to verify compliance with the Federal Performance Standard should be performed
on each oven prior to release to the owner.
BEFORE SERVICING
Before servicing an operative unit, perform a microwave emission check as per the Microwave Measure-
ment Procedure outlined in this service manual.
If microwave emissions level is in excess of the specified limit, contact DACOR immediately @
1-800-793-0093.
If the unit operates with the door open, service person should 1) tell the user not to operate the oven and
2) contact DACOR and Food and Drug Administration's Center for Devices and Radiological Health
immediately.
Servicepersonnel shouldinform DACORof anycertified unitfound withemissions inexcess of4mW/cm2.
Theowneroftheunitshouldbeinstructednottousetheunituntiltheovenhasbeenbroughtintocompliance.
DANGER CAUTION
HIGH VOLTAGE
Do not energize a microwave oven with the outer case cabinet removed, because a microwave oven
generates High Voltage in the circuit.
Ifyou intendtooperatetheovenemployingthe highfrequencyswitchingpowerconvertercircuit,you should
take special precautions to avoid an electrical shock hazard.
The high voltage transformer, high voltage capacitor and high voltage diode have energized high voltage
potential approx. 8 KV.
ThealuminiumheatsinkisconnectedtotheswitchingpowertransistorCollectorpole,andhasanenergized
high voltage potential approx. 650V peak.
DO NOT ACCESS THE HIGH VOLTAGE TRANSFORMER, HIGH VOLTAGE CAPACITOR, HIGH
VOLTAGEDIODEANDHEATSINKWHENTHEPOWERSUPPLYISCONNECTEDTOANELECTRICAL
OUTLET.

1
DMT2420B
DMT2420R
DMT2420S
WARNINGTO SERVICE PERSONNEL
Microwave ovens contain circuitry capable of pro-
ducing very high voltage and current, contact with
following parts
may result in a severe, possibly
fatal, electrical shock.
(Example)
HighVoltageCapacitor,HighVoltagePowerTrans-
former,Magnetron,HighVoltageRectifierAssem-
bly, High Voltage Harness etc..
Read the Service Manual carefully and follow all
instructions.
Before Servicing
1. Disconnect the power supply cord , and then
remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
WARNING:RISK OF ELECTRIC SHOCK.
DISCHARGE THE HIGH-VOLTAGE
CAPACITOR BEFORE SERVICING.
The high-voltage capacitor remains charged about 60
secondsaftertheovenhasbeenswitchedoff.Waitfor60
secondsandthenshort-circuittheconnectionofthehigh-
voltagecapacitor(that is theconnectingleadof the high-
voltage rectifier) against the chassis with the use of an
insulated screwdriver.
Whenever troubleshooting is performed the power supply
mustbedisconnected.Itmay,insomecases,benecessary
to connect the power supply after the outer case has been
removed, in this event,
1. Disconnect the power supply cord, and then remove
outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Disconnect the leads to the primary of the power
transformer.
5. Ensure that the leads remain isolated from other
components and oven chassis by using insulation tape.
6. After that procedure, reconnect the power supply cord.
When the testing is completed,
1. Disconnect the power supply cord, and then remove
outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Reconnect the leads to the primary of the power
transformer.
5. Reinstall the outer case (cabinet).
6. Reconnect thepowersupplycordaftertheoutercase is
installed.
7. Run the oven and check all functions.
After repairing
1. Reconnect all leads removed from components during
testing.
2. Reinstall the outer case (cabinet).
3. Reconnect thepowersupplycordaftertheoutercase is
installed.
4. Run the oven and check all functions.
Microwave ovens should not be run empty. To test for the
presence of microwave energy within a cavity, place a cup
of cold water on the oven turntable, close the door and set
the power to HIGH and set the microwave timer for two (2)
minutes.Whenthetwominuteshaselapsed(timeratzero)
carefully check that the water is now hot. If the water
remainscoldcarryoutBeforeServicing procedureandre-
examine the connections to the component being tested.
When all service work is completed and the oven is fully
assembled,themicrowavepoweroutputshouldbechecked
and a microwave leakage test should be carried out.
Don't Touch !
Danger High Voltage

2
DMT2420B
DMT2420R
DMT2420S
MICROWAVE MEASUREMENT PROCEDURE
A. Requirements:
1) Microwave leakage limit (Power density limit): The power density of microwave radiation emitted by a microwave oven
shouldnotexceed1mW/cm2atanypoint5cmormorefromtheexternalsurfaceoftheoven,measuredpriortoacquisition
bya purchaser,andthereafter (throughtheuseful lifeofthe oven),5mW/cm2at anypoint5cm ormorefrom theexternal
surface of the oven.
2) Safety interlock switches Primary interlock relay and door sensing switch shall prevent microwave radiation emission in
excess of the requirement as above mentioned, secondary interlock switch shall prevent microwave radiation emission
in excess of 5 mW/cm2at any point 5cm or more from the external surface of the oven.
B. Preparation for testing:
Before beginning the actual measurement of leakage, proceed as follows:
1) Make sure that the actual instrument is operating normally as specified in its instruction booklet.
Important:
Survey instruments that comply with the requirement for instrumentation as prescribed by the performance standard for
microwave ovens, 21 CFR 1030.10(c)(3)(i), must be used for testing.
2) Place the oven tray in the oven cavity.
3) Place the load of 275±15 ml (9.8 oz) of tap water initially at 20±5½C (68½F) in the center of the oven cavity.
The water container shall be a low form of 600 ml (20 oz) beaker with an inside diameter of approx. 8.5 cm (3-1/2 in.)
and made of an electrically nonconductive material such as glass or plastic.
Theplacingofthisstandardloadintheovenisimportantnotonlytoprotect the oven, but also to insure that any leakage
is measured accurately.
4) Set the cooking control on Full Power Cooking Mode.
5) Close the door and select a cook cycle of several minutes. If the water begins to boil before the survey is completed,
replace it with 275 ml of cool water.
C. Leakage test:
Closed-door leakage test (microwave measurement)
1) Grasptheprobeofthesurveyinstrumentandholditperpendiculartothegapbetweenthedoorandthebodyoftheoven.
2) Move the probe slowly, not faster than 1 in./sec. (2.5 cm/sec.) along the gap, watching for the maximum indication on
the meter.
3) Checkforleakageatthedoorscreen,sheetmetalseamsandotheraccessiblepositionswherethecontinuityofthemetal
has been breached (eg., around the switches, indicator, and vents).
Whiletestingforleakagearoundthedoorpullthedoorawayfromthefrontoftheovenasfarasispermittedbytheclosed
latch assembly.
4) Measure carefully at the point of highest leakage and make sure that the highest leakage is no greater than 4mW/cm2,
and that the secondary interlock switch does turn the oven OFF before any door movement.
NOTE: After servicing, record data on service invoice and microwave leakage report.

3
DMT2420B
DMT2420R
DMT2420S
SERVICE MANUAL
MICROWAVEOVEN
DMT2420B/DMT2420R/DMT2420S
FOREWORD
This Manual has been prepared to provide Dacor Service Personnel
with Operation and Service Information for the DACOR MICRO-
WAVE OVENS, DMT2420B, DMT2420R and DMT2420S.
Itisrecommendedthatservicepersonnelcarefullystudytheentiretext
of this manual so that they will be qualified to render satisfactory
customer service.
Check the interlock switches and the door seal carefully. Special
attention should be given to avoid electrical shock and microwave
radiationhazard.
WARNING
Never operate the oven until the following points are ensured.
(A) The door is tightly closed.
(B) The door brackets and hinges are not defective.
(C) The door packing is not damaged.
(D) The door is not deformed or warped.
(E) There is no other visible damage with the oven.
Servicing and repair work must be carried out only by trained service
personnel. DANGER
Certaininitialpartsareintentionallynotgroundedandpresent
a risk of electrical shock only during servicing. Service per-
sonnel-Donotcontactthefollowingpartswhiletheappliance
isenergized;
HighVoltageCapacitor,PowerTransformer,Magnetron,High
VoltageRectifierAssembly, HighVoltageHarness;
If provided, Vent Hood, Fan assembly, Cooling Fan Motor.
Allthepartsmarked“*”onpartslistareusedatvoltagesmorethan
250V.
Removal of the outer wrap gives access to voltage above 250V.
Allthepartsmarked“∆”onpartslistmaycauseunduemicrowave
exposure,bythemselves,orwhentheyaredamaged,loosenedor
removed.
PRODUCTDESCRIPTION
GENERALINFORMATION
OPERATION
TROUBLESHOOTINGGUIDEAND
TESTPROCEDURE
TOUCHCONTROLPANEL
COMPONENTREPLACEMENT
ANDADJUSTMENTPROCEDURE
WIRINGDIAGRAM
PARTS LIST
1440 Bridge Gate Dr.
Diamond Bar, CA 91765
dis tinc tive a ppliances
dis tinctive appliances

4
DMT2420B
DMT2420R
DMT2420S
ITEM DESCRIPTION
PowerRequirements 120 Volts / 14.3 Amperes
60Hertz
Singlephase,3wiregrounded
PowerOutput 1200watts(IECTESTPROCEDURE)
Operatingfrequencyof2450MHz
CaseDimensions Width 24"
Height 13-3/8"
Depth 19-1/8"
CookingCavityDimensions Width 17-3/8"
Height 10-1/2"
2.0 Cubic Feet Depth 18-5/8"
ControlComplement Touch Control System
Clock ( 1:00 - 12:59 )
Timer (0 - 99 min. 99 seconds)
MicrowavePowerforVariableCooking
Repetition Rate;
100PERCENT.............................. Fullpowerthroughoutthecooking time
90PERCENT............................................... approx. 90% of Full Power
80PERCENT............................................... approx. 80% of Full Power
70PERCENT............................................... approx. 70% of Full Power
60PERCENT............................................... approx. 60% of Full Power
50PERCENT............................................... approx. 50% of Full Power
40PERCENT............................................... approx. 40% of Full Power
30PERCENT.............................................. approx. 30% of Full Power
20PERCENT............................................... approx. 20% of Full Power
10PERCENT............................................... approx. 10% of Full Power
0PERCENT................................Nopowerthroughoutthecookingtime
Sensor modes pads, Microwave Recipes & Instruction pad, Defrost pad,
Beverage pad, Set Up pad, Number selection pads, Easy Minute pad,
Stop/Clearpad,Start pad,NewWave Cookbook pads.
Oven Cavity Light Yes
SafetyStandard UL Listed FCC Authorized
DHHS Rules, CFR, Title 21, Chapter 1, Subchapter J
SPECIFICATION
GENERAL INFORMATION
GROUNDING INSTRUCTIONS
This oven is equipped with a three prong grounding plug. It must be plugged into a wall receptacle that is properly installed
and grounded in accordance with the National Electrical Code and local codes and ordinances. In the event of an electrical
short circuit, grounding reduces the risk of electric shock by providing an escape wire for the electric current.
WARNING: Improper use of the grounding plug can result in a risk of electric shock.
Electrical Requirements
The electrical requirements are a 120 volt 60 Hz, AC only, 15 or 20 amp. fused electrical supply. It is recommended that a
separate circuit serving only this appliance be provided. When installing this appliance, observe all applicable codes and
ordinances.
A short power-supply cord is provided to reduce risks of becoming entangled in or tripping over a longer cord.

5
DMT2420B
DMT2420R
DMT2420S
Where a two-pronged wall-receptacle is encountered, it is the personal
responsibility and obligation of the customer to contact a qualified
electricianandhaveitreplacedwithaproperlygroundedthree-pronged
wall receptacle or have a grounding adapter properly grounded and
polarized. If the extension cord must be used, it should be a 3-wire, 15
amp.orhigherratedcord.Donotdrapeoveracountertoportablewhere
it can be pulled on by children or tripped over accidentally.
CAUTION: DO NOT UNDER ANY CIRCUMSTANCES CUT OR RE-
MOVE THE ROUND GROUNDING PRONG FROM THIS
PLUG.
OVEN DIAGRAM 1. One touch door open button.
Push to open door.
2. Door latches.
The oven will not operate unless
the door is securely closed.
3. Removable turntable support.
4. Removable turntable.
The turntable will rotate
clockwise or counterclockwise.
5. Oven lamp.
Itwilllightwhenovenisoperating
or door is opened.
6. Oven door with see-through
window.
7. Ventilation openings. (Rear)
8. Auto-Touch control panel.
9. Time display: Digital display, 99
minutes 99 seconds.
10.Wave guide cover.
11.Power supply cord.
NOTE:
Thedirectedfeaturesaredisabled
afterthreeminuteswhentheoven
is not in use. These features are
automatically enabled when the
door is opened and closed or the
STOP/ CLEAR pad is pressed.
3-Pronged
Plug
Grounded
Receptacle Box
Grounding Pin
3-Pronged Receptacle
DMT2420R DMT2420B DMT2420S
1
65
4
210
11
9
7
8
3
TOUCH CONTROL PANEL

6
DMT2420B
DMT2420R
DMT2420S
OPERATION
DESCRIPTION OF OPERATING SEQUENCE
Thefollowingisadescriptionofcomponentfunctionsduring
ovenoperation.
OFF CONDITION
Closing the door activates the door sensing switch and
secondary interlock switch. (In this condition, the monitor
switchcontactsare opened.)
When oven is plugged in, 120 volts A.C. is supplied to the
controlunit.(FigureO-1).
1. "Setclock" keyand"Video demo"keywill beappeared
on the touch screen.
2. Touch"Setclock"keyandset the clock referring to the
operationmanual.
NOTE: Ifanykeysarenottouchedfor30seconds,thetouch
screenwillgoontotheVideoDemomode.Tocancel
theVideoDemomode,touchtheSTOP/CLEARpad.
And then set the clock.
3. Thetouchscreenwillshowthehomepageaftersetting
the clock.
4. The following is the example of the Home page in the
case the time of the day is set to 12:30 p.m..
NOTE: Evenif the clock is not set, the display will show the
HomepagebytouchingtheSTOP/CLEARpadwithin
30 seconds after plugged in.
COOKING CONDITION
Program desired cooking time by touching the NUMBER
pads. Program the power level by touching the POWER
LEVELpad.
When the START pad is touched, the following operations
occur:
1. The contacts of relays are closed and components
connected to the relays are turned on as follows.
(Fordetails, refertoFigureO-2)
RELAY CONNECTEDCOMPONENTS
RY-1 ovenlamp/turntablemotor/fanmotor
RY-2 powertransformer
2. 120 volts A.C. is supplied to the primary winding of the
powertransformerandisconvertedtoabout3.2voltsA.C.
output on the filament winding, and approximately 2360
volts A.C. on the high voltage winding.
3. Thefilamentwindingvoltageheatsthemagnetronfilament
andtheH.V.winding voltageis sentto avoltagedoubler
circuit.
4. The microwave energy produced by the magnetron is
channelled through the waveguide into the cavity feed-
box, and then into the cavity where the food is placed to
becooked.
5. Upon completion of the cooking time, the power
transformer, oven lamp, etc. are turned off, and the
generationofmicrowaveenergyisstopped.Theovenwill
revert to the OFF condition.
6. Whenthedoorisopenedduringacookcycle,themonitor
switch,doorsensingswitch,secondaryinterlockswitch,
relay(RY1)andprimaryinterlockrelayareactivatedwith
the following results. The circuits to the turntable motor,
thecooling fan motor, and the high voltage components
are de-energized, the oven lamp remains on, and the
digital read-out displays the time still remaining in the
cook cycle when the door was opened.
7. Themonitorswitchelectrically monitorstheoperationof
thesecondaryinterlockswitchandprimaryinterlockrelay
andismechanicallyassociatedwiththedoorsothatitwill
functioninthefollowingsequence.
(1) Whenthedooropensfromtheclosedposition,theprimary
interlockrelay(RY2)andsecondaryinterlockswitchopen
their contacts. And contacts of the relay (RY1) remains
closed. Then the monitor switch contacts close.
(2) When the door is closed from the open position, the
monitor switch contacts open first. Then the contacts of
the secondary interlock switch and door sensing switch
close. And contacts of the relay (RY1) open.
Ifthe secondaryinterlockswitchandprimaryinterlockrelay
(RY2)failwiththecontactsclosedwhenthedoorisopened,
the closing of the monitor switch contacts will form a short
circuitthroughthemonitorfuse,secondaryinterlockswitch,
relay (RY1) and primary interlock relay (RY2), causing the
monitor fuse to blow.
POWER LEVEL 0% TO 100% COOKING
WhenVariableCookingPowerisprogrammed,the120volts
A.C. is supplied to the power transformer intermittently
throughthecontactsofrelay(RY-2)whichisoperatedbythe
controlunitwithina32secondtimebase.Microwavepower
operation is as follows:
VARI-MODE ON TIME OFF TIME
100% power 32 sec. 0 sec.
approx. 90% power 30 sec. 2 sec.
approx. 80% power 26 sec. 6 sec.
approx. 70% power 24 sec. 8 sec.
approx. 60% power 22 sec. 10 sec.
approx. 50% power 18 sec. 14 sec.
approx. 40% power 16 sec. 16 sec.
approx. 30% power 12 sec. 20 sec.
approx. 20% power 8 sec. 24 sec.
approx. 10% power 6 sec. 26 sec.
0% power 0 sec. 32 sec.
Time
Select
Kitchen
Timer
12 : 30 PM
123
456
78
0
9

7
DMT2420B
DMT2420R
DMT2420S
Note: TheON/OFFtimeratiodoesnotcorrespondwiththe
percentageofmicrowavepower,becauseapprox.2
seconds are needed for heating of the magnetron
filament.
SENSOR COOKING CONDITION
Using the SENSOR function, the food is cooked without
figuringtime,powerlevelorquantity.Whentheovensenses
enough steam from the food, it relays the information to its
microprocessor which will calculate the remaining cooking
timeandpowerlevelneededforbestresults.Whenthefood
iscooked,watervaporisdeveloped.Thesensor“senses”the
vapor and its resistance increases gradually. When the
resistance reaches the value set according to the menu,
supplementary cooking is started.
Thetimeofsupplementarycookingisdeterminedbyexperi-
ment with each food category and inputted into the LSI.
An example of how sensor works: (POTATOES)
1. Potatoes at room temperature. Vapor is emitted very
slowly.
2. HeatPotatoes.Moistureandhumidityisemittedrapidly.
You can smell the aroma as it cooks.
3. Sensor detects moisture and humidity and calculates
cookingtimeandvariablepower.
CookingSequence.
1. TouchoneoftheSENSORpadsandthentouchtheStart
pad.
NOTE: The oven should not be operated on SENSOR
immediately after plugging in the unit. Wait two
minutesbeforecooking on SENSOR.
2. Thecoilofshut-offrelay(RY-1)isenergized,theturntable
motor,ovenlampandcoolingfanmotorareturnedon,but
thepowertransformeris not turned on.
3. Afterabout16seconds,thecookrelay(RY-2)isenergized.
Thepowertransformeristurnedon,microwaveenergyis
produced and first stage is started.
The16secondsisthecoolingtimerequiredtoremoveany
vapor from the oven cavity and sensor.
NOTE: Duringthisfirststage,donotopenthedoorortouch
STOP/CLEARpad.
4. Whenthesensordetectsthevaporemittedfromthefood,
the display switches over to the remaining cooking time
and the timer counts down to zero.
At this time, the door may be opened to stir, turn, or
seasonfood.
5. Whenthetimer reaches zero, an audible signal sounds.
Theshut-offrelayandcookrelayarede-energizedandthe
power transformer, oven lamp, etc. are turned off.
6. OpeningthedoorortouchingtheSTOP/CLEARpad,the
timeof daywillreappear onthedisplayandthe ovenwill
revert to an OFF condition.
MICROWAVE
MICROWAVE
AH SENSOR

8
DMT2420B
DMT2420R
DMT2420S
Figure O-1. Oven Schematic-Off Condition
SCHEMATIC
NOTE: CONDITION OF OVEN
1. DOOR CLOSED.
2. CLOCK APPEARS ON DISPLAY.
SCHEMATIC
NOTE: CONDITION OF OVEN
1. DOOR CLOSED.
2. COOKING TIME PROGRAMMED.
3. VARIABLE COOKING CONTROL "P-HI/ 100 PERCENT".
4. "START" PAD TOUCHED.
Figure O-2. Oven Schematic-Cooking Condition
NOTE: Indicates components with potential above 250 V.
HIGH
VOLTAGE
RECTIFIER
HIGH
VOLTAGE
CAPACITOR
POWER
TRANSFORMER
MAGNETRON
RED
WHT
WHT RED
MONITOR
SWITCH
(RY1) (RY2)
DOOR
SENSING
SWITCH
FAN
MOTOR
OVEN
LAMP
WHT
SECONDARY
INTERLOCK
SWITCH
TURN
TA B L E
MOTOR
WHT
A1
120V AC
60Hz
N
GND
GRN
C/T
FUSE
RED
COM
SENSOR
CONTROL UNIT
BLK
H
A2
CAVITY
TEMP
FUSE
HUMIDITY
N.O.
N.C.
COM
ORG
BRN
ORG
WHT WHT
F3
F2
F1
B2
B1
COM
N.O.
BLU
PRIMARY
INTERLOCK
RELAY
N.O.
WHT
N.O.
GRY/WHT
RED
COM
BRN
BLU
ORG
OL
TTM
FM
HIGH
VOLTAGE
RECTIFIER
HIGH
VOLTAGE
CAPACITOR
POWER
TRANSFORMER
MAGNETRON
RED
WHT
WHT RED
MONITOR
SWITCH
(RY1) (RY2)
DOOR
SENSING
SWITCH
FAN
MOTOR
OVEN
LAMP
WHT
SECONDARY
INTERLOCK
SWITCH
TURN
TA B L E
MOTOR
WHT
A1
120V AC
60Hz
N
GND
GRN
C/T
FUSE
RED
COM
SENSOR
CONTROL UNIT
BLK
H
A2
CAVITY
TEMP
FUSE
HUMIDITY
N.O.
N.C.
COM
ORG
BRN
ORG
WHT WHT
F3
F2
F1
B2
B1
COM
N.O.
BLU
PRIMARY
INTERLOCK
RELAY
N.O.
WHT
N.O.
GRY/WHT
RED
COM
BRN
BLU
ORG
OL
TTM
FM

9
DMT2420B
DMT2420R
DMT2420S
DESCRIPTION AND FUNCTION OF COMPONENTS
DOOR OPEN MECHANISM
Thedoorisopenedbypushingtheopenbuttononthecontrol
panel, refer to the Figure D-1. When the open button is
pushed,theopenbuttonpushesuptheswitchlever,andthen
the switch lever pushes up the latch head. The latch heads
are moved upward and released from latch hook. Now the
doorwillopen.
FigureD-1. DoorOpen Mechanism
DOOR SENSING AND SECONDARY INTERLOCK
SWITCHES
The secondary interlock switch is mounted in the lower
positionofthelatch hookand thedoorsensingswitchinthe
secondaryinterlocksystemismountedintheupperposition
of the latch hook. They are activated by the latch heads on
thedoor.Whenthedoorisopened,theswitchesinterruptthe
power to all high voltage components. A cook cycle cannot
take place until the door is firmly closed thereby activating
both interlock switches. The secondary interlock system
consistsofthedoorsensingswitchandsecondaryinterlock
relay located on the control circuit board.
MONITOR SWITCH
Themonitorswitchisactivated(thecontactsopened)bythe
latchheadonthedoorwhilethedoorisclosed.Theswitchis
intendedtorendertheoveninoperative,bymeansofblowing
theC/Tfuse,whenthecontactsoftheprimaryinterlockrelay
(RY2) and secondary interlock switch fail to open when the
doorisopened.
Functions:
1. Whenthedoorisopened,themonitorswitchcontactclose
(totheONcondition)duetotheirbeingnormallyclosed.At
thistimetheprimaryinterlock relay (RY2) and secondary
interlock switch are in the OFF condition (contacts open)
dueto their being normally open contact switches.
2. As the door goes to a closed position, the monitor switch
contactsarefirstopenedandthenthedoorsensingswitch
and the secondary interlock switch contacts close. (On
openingthedoor,eachoftheseswitchesoperateinversely.)
3. Ifthedoorisopened,andtheprimaryinterlockrelay(RY2)
andsecondaryinterlock switchcontactsfail toopen,the
C/Tfuseblowssimultaneouslywithclosingofthemonitor
switch contacts.
CAUTION: BEFORE REPLACING A BLOWN C/T FUSE
TEST THE DOOR SENSING SWITCH, PRI-
MARY INTERLOCK RELAY (RY2), RELAY
(RY1),SECONDARYINTERLOCKSWITCHAND
MONITOR SWITCH FOR PROPER OPERA-
TION.(REFER TO CHAPTER "TEST PROCE-
DURE").
NOTE: C/T FUSE AND MONITOR SWITCH ARE
REPLACEDASAN ASSEMBLY.
TURNTABLE MOTOR
The turntable motor rotates the turntable located on the
bottomoftheoven cavity, so that the foods ontheturntable
cookevenlyduringcooking.Theturntablemayturnineither
direction.
COOLING FAN MOTOR
Thecoolingfanmotordrivesabladewhichdrawsexternalcool
air.This coolairis directedthroughthe airvanessurrounding
themagnetronandcoolsthemagnetron.Thisairischanneled
throughtheovencavitytoremovesteamandvaporsgivenoff
from the heating foods. It is then exhausted through the
exhausting air vents at the oven cavity.
CAVITY TEMPERATURE FUSE
The cavity temperature fuse located on the top of the oven
cavity,isdesignedtopreventdamagetotheovenbyfire.Ifthe
foodloadis overcooked,byeithererror incooktimeor defect
in the control unit, the cavity temperature fuse will open.
Undernormaloperation,thecavitytemperaturefuseremains
closed. However, when abnormally high temperatures are
reachedwithintheovencavity,thecavitytemperaturefusewill
openat 302OF(150OC)causingtheoventoshutdown.
NOTE: This is fuse. It does not reset.
C/T TEMPERATURE FUSE
TheC/Tfuselocatednearthemagnetronisdesignedtoprevent
damagetothemagnetronifanoverheatedconditiondevelops
inthetubeduetocoolingfanfailure,obstructedairguide,dirty
or blocked air intake, etc.
Under normal operation, the C/T fuse remains closed. How-
ever,when abnormallyhightemperatures arereachedwithin
themagnetron,theC/Tfusewillopenat302OF(150OC)causing
the oven to shut down.
1. TheC/Tfuseblows whenthecontacts(COM-NO)ofthe
primary interlock relay (RY2) and secondary interlock
switchremain closedwiththe ovendooropenandwhen
the monitor switch closes.
2. If the wire harness or electrical components are short-
circuited, this monitor fuse blows to prevent an electric
shock or fire hazard.
NOTE: This is fuse. It does not reset.
Door Sensing
Switch
Monitor Switch
Switch Lever
Secondary Interlock
Switch
Latch Heads
Door

10
DMT2420B
DMT2420R
DMT2420S
TROUBLESHOOTING GUIDE
Never touch any part in the circuit with your hand or an uninsulated tool while the power supply is connected.
Whentroubleshooting themicrowave oven,itishelpfultofollowthe Sequenceof Operationinperformingthechecks.Many
ofthepossiblecausesoftroublewillrequirethataspecifictestbeperformed.Thesetestsaregivenaprocedureletterwhich
will be found in the "Test Procedure "section.
IMPORTANT: IftheovenbecomesinoperativebecauseofablownC/Tfuse,checkthemonitorswitch,relay(RY1)primary
interlockrelay(RY2),doorsensingswitchandsecondaryinterlockswitchbeforereplacingtheC/Tfuse.Ifthe
C/T fuse is replaced, the monitor switch must also be replaced. Use part FFS-BA019/KIT as an assembly.
IMPORTANT: Whenevertroubleshootingisperformedwiththepowersupplycorddisconnected.Itmayin,somecases,be
necessary to connect the power supply cord after the outer case has been removed, in this event:
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Dischargehighvoltagecapacitor.
4. Disconnect the leads to the primary of the power transformer.
5. Ensurethattheleadsremainisolatedfromother componentsand ovenchassis byusinginsulationtape.
6. Afterthatprocedure, reconnect the power supply cord.
Whenthe testingis completed
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Dischargehighvoltagecapacitor.
4. Reconnect the leads to the primary of the power transformer.
5. Reinstalltheoutercase(cabinet).
6. Reconnect the power supply cord after the outer case is installed.
7. Run the oven and check all functions.

11
DMT2420B
DMT2420R
DMT2420S
CK = Check / RE = Replace
AMAGNETRONASSEMBLYTEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Dischargehighvoltagecapacitor.
4. To test for an open filament, isolate the magnetron from the high voltage circuit. A continuity check across the
magnetron filament leads should indicate less than 1 ohm.
5. To test for a shorted magnetron, connect the ohmmeter leads between the magnetron filament leads and chassis
ground. This test should indicate an infinite resistance. If there is little or no resistance the magnetron is grounded
andmustbereplaced.
SHORT IN POWER CORD SHORT OR OPENED WIRING MAGNETRON POWER TRANSFORMER H.V. RECTIFIER ASSEMBLY HIGH VOLTAGE CAPACITOR CAVITY TEMPERATURE FUSE C/T FUSE SECONDARY INTERLOCK SYSTEM PRIMARY INTERLOCK RELAY MONITOR SWITCH C/T FUSE OVEN LAMP OR SOCKET COOLING FAN MOTOR TURNTABLE MOTOR TOUCH CONTROL PANEL WRONG OPERATION LOW VOLTAGE DIRTY OVEN CAVITY KEY UNIT RELAY (RY1) DEFROST CENTER FOIL PATTERN ON PWB. AH SENSOR
Home fuse or circuit breaker blows when
power cord is plugged into wall receptacle.
Monitor fuse blows when power cord is
plugged into wall receptacle.
Any letters or indicators do not appear in
display when power cord is first plugged
into wall outlet.
Display does not operate properly when
STOP/CLEAR key is touched. (Buzzer
should sound and ":" or time of day
should appear in display.)
Oven lamp does not light when door is
opened.
Oven lamp does not go out when door is
closed.
Oven lamp lights but fan motor and
turntable motor do not operate.
Oven does not go into cook cycle when
START pad is touched
Oven seems to be operating but little or
no heat is produced in oven load. (Food
incompletely cooked or not cooked at all
at end of cook cycle.)
Oven goes into a cook cycle but
extremely uneven heating is produced in
oven load (food).
Oven does not cook properly when
programmed for P-50/ 50 PERCENT
mode. (Operates properly on P-HI/ 100
PERCENT mode.)
Oven goes into Defrost Center but food
is not defrosted well.
AH sensor does not end during Sensor
cooking condition. (Oven does not shut
off after a cup of water is boiling by
sensor cooking.)
Oven stops at 16 sec. after starting.
RE RE ABCDEEFFGH RE RE CK I CK CK CK JKLMN
TEST PROCEDURE
POSSIBLE CAUSE
AND
DEFECTIVE PARTS
COOKING
CONDITION
CONDITION
PROBLEM
OFF
CONDITION
SENSOR
COOKING
CONDITION

12
DMT2420B
DMT2420R
DMT2420S
(HIGHVOLTAGES AREPRESENTAT THEHIGHVOLTAGE TERMINAL,SODO NOTATTEMPTTO
MEASURETHE FILAMENT AND HIGH VOLTAGE.)
BPOWERTRANSFORMERTEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Dischargehighvoltagecapacitor.
4. Disconnect the primary input terminals and measure the resistance of the transformer with an
ohmmeter. Check for continuity of the coils with an ohmmeter. On the R x 1 scale, the resistance of
the primary coil should be less than 1 ohm and the resistance of the high voltage coil should be
approximately 90 ohms; the resistance of the filament coil should be less than 1 ohm.
5. Reconnectall leads removed fromcomponentsduringtesting.
6. Reinstalltheoutercase(cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
6. Reconnectall leads removed fromcomponentsduringtesting.
7. Reinstalltheoutercase(cabinet).
8. Reconnect the power supply cord after the outer case is installed.
9. Run the oven and check all functions.
MICROWAVE OUTPUT POWER
Thefollowingtestprocedureshouldbecarriedoutwiththemicrowaveoveninafullyassembledcondition
(outer case fitted).
HIGHVOLTAGESAREPRESENTDURINGTHECOOKCYCLE,SOEXTREMECAUTIONSHOULDBE
OBSERVED.
Power output of the magnetron can be measured by performing a water temperature rise test. This test
shouldonlybeusedifabovetestsdonotindicateafaultymagnetronandthereisnodefectinthefollowing
componentsorwiring:siliconrectifier,highvoltagecapacitorandpowertransformer.Thistestwillrequire
a 16 ounce (453cc) measuring cup and an accurate mercury thermometer or thermocouple type
temperaturetester.Foraccurateresults,thefollowingproceduremust be followed carefully:
1. Fillthemeasuringcupwith16oz.(453cc)oftapwaterandmeasurethetemperatureofthewaterwith
athermometerorthermocoupletemperaturetester.Stirthethermometerorthermocouplethroughthe
wateruntilthetemperaturestabilizes. Record the temperature of the water.
2. Placethecupofwaterintheoven.Operateovenat100PERCENTPOWER/P-HIselectingmorethan
60 seconds cook time. Allow the water to heat for 60 seconds, measuring with a stop watch, second
handofawatchor the digital read-out countdown.
3. Removethecupfromtheovenandagainmeasurethetemperature,makingsuretostirthethermometer
orthermocouplethroughthewateruntilthemaximumtemperatureisrecorded.
4. Subtractthe coldwatertemperaturefrom thehotwatertemperature. Thenormalresult should be33
to62½F(18.6to34.5½C)riseintemperature.Ifthewatertemperaturesareaccuratelymeasuredand
testedfortherequiredtimeperiodthetestresultswillindicateifthemagnetrontubehaslowpoweroutput
(lowriseinwatertemperature)whichwouldextendcookingtimeorhighpoweroutput(highriseinwater
temperature)whichwouldreducecookingtime.Becausecookingtimecanbeadjustedtocompensate
forpoweroutput,themagnetrontubeassemblyshouldbereplacedonlyifthewatertemperaturerise
testindicatesapoweroutputwellbeyondthenormallimits.Thetestisonlyaccurateifthepowersupply
line voltage is 120 volts and the oven cavity is clean.

13
DMT2420B
DMT2420R
DMT2420S
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Dischargehighvoltagecapacitor.
4. Ifthecapacitorisopen,nohighvoltagewillbeavailabletothemagnetron.Disconnectinputleadsand
check for short or open between the terminals using an ohmmeter.
Checkingwithahighohmscale,ifthehighvoltagecapacitorisnormal,themeterwillindicatecontinuity
for a short time and should indicate an open circuit once the capacitor is charged. If the above is not
thecase,check the capacitor with an ohmmeter to see if it is shorted between either of the terminals
and case. If it is shorted, replace the capacitor.
5. Reconnectall leads removed fromcomponentsduringtesting.
6. Reinstalltheoutercase(cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
DHIGHVOLTAGECAPACITORTEST
ECAVITY TEMPERATURE FUSE TEST
CHIGHVOLTAGE RECTIFIER TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Dischargehighvoltagecapacitor.
4. Isolatetherectifierfromthecircuit.Usingthehighestohmscaleofthemeter,readtheresistanceacross
theterminalsandobserve,reversetheleadstotherectifierterminalsandobservemeterreading.Ifa
short is indicated in both directions, or if an infinite resistance is read in both directions, the rectifier
isprobablydefective and should be replaced.
5. Reconnectallleads removed from componentsduringtesting.
6. Reinstalltheoutercase(cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
NOTE:Be sureto useanohmmeter thatwill supplya forwardbiasvoltage ofmore than6.3 volts.
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Dischargehighvoltagecapacitor.
4. Acontinuitycheckacrossthecavitytemperaturefuseterminalsshouldindicateaclosedcircuitunless
thetemperatureofthe cavitytemperaturefusereachesapproximately302OF(150OC). Anopen cavity
temperaturefuseindicatesoverheatingoftheoven,exchangethe cavitytemperaturefuseandcheck
inside of oven cavity and for improper setting of cooking time or operation of control unit. Check for
restricted air flow through the vent holes of the oven cavity, especially the cooling fan and air guide.
5. Reconnectall leads removed fromcomponentsduringtesting.
6. Reinstalltheoutercase(cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
C/T FUSE TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Dischargehighvoltagecapacitor.
4. AcontinuitycheckacrosstheC/Tfuseterminalsshouldindicateaclosedcircuitunlessthetemperature
ofthe C/Tfuse reachesapproximately302OF(150OC).AnopenC/Tfuseindicatesoverheatingofthe
magnetron. Check for restricted air flow to the magnetron, especially the cooling fan air guide.
CAUTION: IF THE TEMPERATURE FUSE INDICATES AN OPEN CIRCUIT AT ROOM
TEMPERATURE,REPLACE TEMPERATUREFUSE.
5. If the C/T fuse is blown when the door is opened, check the primary interlock relay, secondary
interlock switch and monitor switch according to the "TEST PROCEDURE" for those switches before
replacingtheblownmonitor fuse.

14
DMT2420B
DMT2420R
DMT2420S TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
CAUTION: BEFORE REPLACING A BLOWN C/T FUSE, TEST THE PRIMARY INTERLOCK RELAY,
SECONDARYINTERLOCKSWITCH,DOORSENSINGSWITCHANDMONITORSWITCH
FORPROPEROPERATION.
IftheC/Tfuse isblownbyimproperswitchoperation,theC/Tfuseandmonitorswitchmustbereplaced
with"C/Tfuseandmonitorswitchassembly"partnumberFFS-BA019/KIT,evenifthemonitorswitch
operatesnormally. TheC/Tfuseandmonitor switchassemblyis comprisedofa20ampere fuseand
switch.
6. Reconnectall leads removed fromcomponentsduringtesting.
7. Reinstalltheoutercase(cabinet).
8. Reconnect the power supply cord after the outer case is installed.
9. Run the oven and check all functions.
DOORSENSINGSWITCH
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Dischargehighvoltagecapacitor.
4. Isolatetheswitchandconnecttheohmmetertothecommon(COM.)andnormallyopen(NO)terminal
of the switch. The meter should indicate an open circuit with the door open and a closed circuit with
the door closed. If improper operation is indicated, replace the door sensing switch.
5. Reconnectall leads removed fromcomponentsduringtesting.
6. Reinstalltheoutercase(cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
NOTE: Ifthedoorsensingswitchcontactsfailintheopenpositionandthedoorisclosed,thecoolingfan,
turntable and oven light will be activated by RY1.
PRIMARYINTERLOCKRELAY(RY2)
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Dischargehighvoltagecapacitor.
4. Disconnecttwo(2)wireleadsfromthemaletabterminalsoftheSecondaryInterlockRelay.Checkthe
stateoftherelaycontactsusingaohmmeter.Therelaycontactsshouldbeopen.Iftherelaycontacts
are closed, replace the circuit board entirely or the relay itself.
5. Reconnectall leads removed fromcomponentsduringtesting.
6. Reinstalltheoutercase(cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
F SECONDARYINTERLOCKSYSTEMTEST

15
DMT2420B
DMT2420R
DMT2420S
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
The touch control panel consists of circuits including semiconductors such as LSI, ICs, etc. Therefore,
unlikeconventionalmicrowaveovens,propermaintenancecannotbeperformedwithonlyavoltmeterand
ohmmeter.Inthisservicemanual,thetouchcontrolpanelassemblyisdividedintotwounits,ControlUnit
and Key Unit, and also the Control Unit is divided into two units, LSI Unit and Power Unit, and
troubleshooting by unit replacement is described according to the symptoms indicated.
Beforetesting,
1) Disconnect the power supply cord, and then remove outer case.
2) Open the door and block it open.
3) Dischargehighvoltagecapacitor.
4) Disconnect the leads to the primary of the power transformer.
5) Ensurethatthese leadsremainisolated fromothercomponents andovenchassisbyusing insulationtape.
1. Key Unit.
NOTE :
1)CheckKey unitribbonconnection beforereplacement.
2)Re-installtheoutercase(cabinet).
3) Reconnect the power supply cord after the outer case is installed.
4) Run the oven and check all functions.
The following symptoms indicate a defective key unit.
a) When touching the pads, a certain pad produces no signal at all.
b) When touchinganumberpad, two figuresormoreare displayed.
c) When touching the pads, sometimes a pad produces no signal.
If the Key unit is defective.
HTOUCHCONTROLPANELASSEMBLYTEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Dischargehighvoltagecapacitor.
4. Before performing this test, make sure that the secondary interlock switch and the primary interlock
relayareoperatingproperly,accordingtotheaboveSwitchTestProcedure.Disconnectthewirelead
fromthemonitorswitch(COM)terminal. Check the monitor switch operation by usingtheohmmeter
asfollows.Whenthedoorisopen,themetershouldindicateaclosedcircuit.Whenthemonitorswitch
actuatorispushedbyascrewdriverthroughthelowerlatch hole on the front plate of the oven cavity
withthedooropened(inthisconditiontheplungerofthemonitorswitchispushedin),themetershould
indicate an open circuit. If improper operation is indicated, the switch may be defective. After testing
the monitor switch, reconnect the wire lead to the monitor switch (COM) terminal and check the
continuity of the monitor circuit.
5. Reconnectall leads removed fromcomponentsduringtesting.
6. Reinstalltheoutercase(cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
GMONITORSWITCHTEST
Secondary
Interlock Switch Monitor Switch
Screw Driver
Ohmmeter
Red White/ White

16
DMT2420B
DMT2420R
DMT2420S
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
1) Disconnect the power supply cord, and then remove outer case.
2) Open the door and block it open.
3) Dischargehighvoltagecapacitor.
4) Replace the Key unit.
5) Reconnect all leadsremovedfromcomponents during testing.
6) Re-install the outercase(cabinet).
7) Reconnect the power supply cord after the outer case is installed.
8) Run the oven and check all functions.
2. ControlUnit
Thefollowingsymptomsindicateadefectivecontrolunit.Beforereplacingthecontrolunit,performthe
Key unit test (Procedure J) to determine if control unit is faulty.
2-1 In connection with pads.
a) When touching the pads, a certain group of pads do not produce a signal.
b) When touching the pads, no pads produce a signal.
2-2 In connection with indicators
a) At a certain digit, all or some segments do not light up.
b) At a certain digit, brightness is low.
c) Only one indicator does not light.
d) The corresponding segments of all digits do not light up; or they continue to light up.
e) Wrongfigureappears.
f) A certain group of indicators do not light up.
g) The figure of all digits flicker.
2-3 Other possible problems caused by defective control unit.
a) Buzzer does not sound or continues to sound.
b) Clockdoesnotoperateproperly.
c) Cooking is not possible.
When testing is completed,
1) Disconnect the power supply cord, and then remove outer case.
2) Open the door and block it open.
3) Dischargehighvoltagecapacitor.
4)Reconnectallleadsremovedfrom components during testing.
5)Re-installtheoutercase(cabinet).
6) Reconnect the power supply cord after the outer case is installed.
7) Run the oven and check all functions..
IKEY UNIT TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3.Dischargehighvoltagecapacitor.
4. If the display fails to clear when the STOP/CLEAR pad is depressed, first verify the flat ribbon cable
ismakinggoodcontact,verifythatthedoorsensingswitch(stopswitch)operatesproperly;thatisthe
contactsareclosedwhenthedoorisclosedandopenwhenthedoorisopen.Ifthedoorsensingswitch
(stopswitch)isgood,disconnecttheflatribboncablethatconnectsthekeyunittothecontrolunitand
make sure the door sensing switch is closed (either close the door or short the door sensing switch
connecter).UsetheKeyunitmatrixindicatedonthecontrolpanelschematicandplaceajumperwire
betweenthepinsthatcorrespondtotheSTOP/CLEARpadmakingmomentarycontact.Ifthecontrol
unitrespondsbyclearingwithabeepthekeyunitisfaultyandmustbereplaced.Ifthecontrolunitdoes
not respond, it is faulty and must be replaced. If a specific pad does not respond, the above method
may be used (after clearing the control unit) to determine if the control unit or key pad is at fault.
5. Reconnect all leads removed from components during testing.

17
DMT2420B
DMT2420R
DMT2420S
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
2. Open the door and block it open.
3. Dischargehighvoltagecapacitor.
4. Disconnect the leads to the primary of the power transformer.
5. Ensurethattheseleadsremainisolatedfromothercomponentsandovenchassisbyusinginsulation
tape.
6. Afterthat procedure, re-connectthepower supply cord.
7. RemovetheoutercaseandcheckvoltagebetweenPinNo.1ofthe2pinconnector(A)andthecommon
terminal of the relay RY1 on the control unit with an A.C. voltmeter.
The meter should indicate 120 volts, if not check oven circuit.
RY1 and RY2 Relay Test
Theserelaysareoperated by D.C. voltage
Check voltage at the relay coil with a D.C. voltmeter during the microwave cooking operation.
DC.voltageindicated.......................... Defective relay.
DC. voltagenot indicated .................... Check diode which is connected to the relay coil. If diode
is good, control unit is defective.
RELAY SYMBOL OPERATIONAL VOLTAGE CONNECTED COMPONENTS
RY1 Approx. 24.0V D.C. Oven lamp / Turntable motor / Cooling fan motor
RY2 Approx. 23.0V D.C. Power transformer
8. Disconnect the power supply cord, and then remove outer case.
9. Open the door and block it open.
10.Dischargehighvoltagecapacitor.
11.Reconnect all leadsremovedfromcomponentsduring testing.
12.Re-install the outercase(cabinet).
13.Reconnect the power supply cord after the outer case is installed.
14.Run the oven and check all functions.
JRELAY TEST
WARNING: Theovenshouldbefullyassembledbeforefollowingprocedure.
(1) Place one cup of water in the center of the turntable tray in the oven cavity.
(2) Close the door, touch the Defrost pad and select 6 Choices. Then select Steaks/Chops/Fish.
(Now, weight 0.5lb is set.) And then touch the start pad.
(3) The oven is in Defrost cooking condition.
(4) The oven will operate as follows
KCOMPUDEFROSTTEST
6. Re-install the outer case (cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
G 5
G 1
SETUP
PASTA
GRAINS
DEFROST
FROZEN
FOOD
EASY
MINUTE
START
TOUCH SCREEN
KEY UNIT
POPCORN
MEATS
STOP
CLEAR
MICROWAVE
RECIPES &
INSTRUCTIONS
FISH
SEAFOOD
REHEAT
BEVERAGES
VEGETABLES
BAKED
POTATOES
POULTRY
G 2 G 3 G14 G 7 G 8 G 9 G10 G14
G6
G13
G12
G11
G15

18
DMT2420B
DMT2420R
DMT2420S
Toprotecttheelectroniccircuits,thismodelisprovidedwithafinefoilpatternaddedtotheprimaryonthe
PWB, this foil pattern acts as a fuse.
1. Foil pattern check and repairs.
1) Disconnect the power supply cord, and then remove outer case.
2) Open the door and block it open.
3) Dischargehighvoltagecapacitor.
4) Followthetroubleshootingguidegivenbelowforrepair.
STEPS OCCURRENCE CAUSE OR CORRECTION
1 Only pattern at "a" is broken. *Insert jumper wire J1 and solder.
2 Pattern at "a" and "b" are broken. *Insert the coil RCILF2003YAZZ between "c" and "d".
5) Make a visual inspection of the varistor.
Checkforburndamageandexaminethe
transformerwithatesterforthepresence
of layer short-circuit (check the primary
coil resistance which is approximately
210ý±15%).Ifanyabnormalconditionis
detected, replace the defective parts.
6) Reconnect all leadsremovedfromcomponents during testing.
7) Re-install the outercase(cabinet).
8) Reconnect the power supply cord after the outer case is installed.
9) Run the oven and check all functions.
2. Followthetroubleshootingguidegivenbelow,ifindicatordoesnotlightupafterabovecheckandrepairs
arefinished.
1) Disconnect the power supply cord, and then remove outer case.
2) Open the door and block it open.
3) Dischargehighvoltagecapacitor.
4) Disconnect the leads to the primary of the power transformer.
5) Ensure that these leads remain isolated from other components and oven chassis by using
insulationtape.
6) After that procedure, reconnect thepowersupplycord.
7) Followthetroubleshootingguidegivenbelowforrepair.
STEPS OCCURRENCE CAUSE OR CORRECTION
The rated AC voltage is not present between
1 Pin No. 1 of the 2-pin connector (A) and the Check supply voltage and oven power cord.
common terminal of the relay RY1.
2The rated AC voltage is present at primary Low voltage transformer or secondary circuit defective.
side of low voltage transformer. Check and repair.
8) Disconnect the power supply cord, and then remove outer case.
9) Open the door and block it open.
LFOILPATTERN ON THEPRINTED WIRINGBOARD TEST
WEIGHT 1ST STAGE 2NDSTAGE
LEVEL TIME LEVEL TIME
0.5lb 70% 30sec. 40% 15sec.
(5) If improper operation is indicated, the control unit is probably defective and should be checked.
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
(J1)
VRS1
RY1
a
b
d
c