LG MD-2642KT Service Manual Download Page 25 | Manualshive

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5-15

NOTE: A MICROWAVE ENERGY LEAKAGE TEST MUST ALWAYS BE PERFORMED WHEN THE UNIT IS

SERVICED FOR ANY REASON.

(3) CHECKOUT PROCEDURES FOR CIRCUIT

BOARD

The following symptoms indicate a defective circuit
board.
(1) The start function fails to operate but the high

voltage Systems, the interlock switches, the
door sensing and the relay check good.

(2) The unit with a normal relay continuously

operates.

(3) The buzzer does not sound or continues to

sound.

(4) Some segments of one or more digits do not light

up, or they continue to light up, or segments light
when they should not.

(6) Wrong figures appear.
(7) The figures of all digits flicker.
(8) Some of the indicators do no light up.
(9) The clock does not keep time properly.

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Summary of Contents for MD-2642KT

Page 1: ...MICROWAVE OVEN SERVICE MANUAL MODEL MD 2642KT CAUTION BEFORE SERVICING THE UNIT READ THE SAFETY PRECAUTIONS IN THIS MANUAL Website http biz lgservice com ...

Page 2: ...eration 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 the magnetron wave guide or transmission line and cavity for proper alignment integrity and connections D Any de...

Page 3: ... CIRCUIT DESCRIPTION 4 4 SERVICE INFORMATION 5 1 TOOLS AND MEASURING INSTRUMENTS 5 1 MICROWAVE LEAKAGE TEST 5 1 MEASUREMENT OF MICROWAVE POWER OUTPUT 5 3 DISASSEMBLY AND ADJUSTMENT 5 3 INTERLOCK CONTINUITY TEST 5 7 COMPONENT TEST PROCEDURE 5 8 TROUBLE SHOOTING 5 11 EXPLODED VIEW 6 1 REPLACEMENT PARTS LIST 7 1 SCHEMATIC DIAGRAM OF P C B 8 1 PRINTED CIRCUIT BOARD 8 2 P C B PARTS LIST 9 1 CONTENTS ...

Page 4: ...rounded 2 450 MHz 2M214 39F 0 99 min 99 sec 618 W x 357 H x 467 D mm 343 W x 221 H x 361 D mm 15 7 kg approx 17 7 kg approx Touch Control System Microwave Power for Variable Cooking Power level HIGH Full power throughout the cooking time 9 Saute approx 90 of Full power 8 Reheat approx 80 7 Med High approx 70 6 Medium approx 60 5 Med Low approx 50 4 Defrost approx 40 3 Low approx 30 2 Simmer approx...

Page 5: ... operation of the microwave oven requires that the magnetron be assembled to the waveguide and cavity Never operate the magnetron unless it is properly installed Be sure that the magnetron gasket is properly installed around the dome of the tube whenever installing the magnetron 2 1 CAUTIONS Unlike other appliances the microwave oven is high voltage and high current equipment Though it is free fro...

Page 6: ...age the electronic or mechanical parts of the unit Do not install the oven next to a conventional surface unit or above a conventional wall oven 5 Use microwave oven in an ambient temperature less than 104 F 40 C 6 Place the microwave oven on a sturdy and flat surface at least 10 cm 4 inches from the wall 7 Place the microwave oven as far away as possible from TV RADIO COMPUTER etc to prevent inte...

Page 7: ...and indicators that tell you time of day cooking time settings and cooking functions selected 2 STOP CLEAR Touch this pad to stop the oven or clear entries 3 START Touch this pad to start all entries except the Auto Cook and Add Minute function which start automatically and to turn Child Lock on or off 4 AUTO COOK Touch this pad to select programming food items 5 ADD MINUTE Touch this pad to cook ...

Page 8: ...r food in decimal increments from 0 1 to 6 0 pounds 4 Touch START 5 At beeping turn food over by following the instructions in the manual 6 After turning food over touch START to resume defrosting 6 TIMED COOKING 1 Touch STOP CLEAR 2 Touch COOK TIME 3 Touch number for cooking time 4 Touch POWER 5 Touch number for cooking power level 6 Touch START 7 MULTI STAGE COOKING 1 Touch STOP CLEAR 2 Touch CO...

Page 9: ...CAPACITOR H V DIODE MONITOR SWITCH BL HIGH VOLTAGE TRANSFORMER BN H V CHOKE FILTER OPTION FA F RELAY 2 RELAY2 Capacitor by shorting the negative high voltage Discharge the high voltage L V TRANSFORMER BEFORE SERVICING POWER AND Terminal of it to chassis ground THERMISTOR LED LAMP WH BK CN2 3 1 WH WH CN1 1 CN3 2 1 CIRCUIT BOARD RELAY1 CONTROL RELAY4 4 3 5 7 8 PK BN 9 YL GN RELAY3 COLOR YELLOW BLACK...

Page 10: ...roximately 2100 volts AC is generated in the secondary of the high voltage transformer which is increased by the action of the high voltage diode and charging of the high voltage capacitor The negative 4 000 Volts DC is applied to the filament of the magnetron WHEN THE OVEN IS SET AT ANY LEVEL EXCEPT MAXIMUM The micom controller controls the ON OFF time of relay 2 by the applied signal to vary the...

Page 11: ...r which is graduated to 600 cc and place the beaker on the center of the turntable Set the energy leakage monitor to 2 450 MHz and use it following the manufacturer s recommended test procedure to assure correct result When measuring the leakage always use the 2 inch 5cm spacer supplied with the probe Operate the oven at its maximum output Measure the microwave radiation using and electromagnetic ...

Page 12: ...touching 1 and then 0 three times 1000 appears in the display window D Touch the START key Make sure the cavity light comes on The unit will begin cooking and the display window will show the time counting down by seconds E After about 5 minutes make sure the primary interlock switch the secondary interlock switch and the interlock monitor and oven lamp switch operate properly by opening and closi...

Page 13: ...he outer case is installed and after all necessary components are replaced or adjusted Special care should be taken in measuring the following parts Circled area of Fig below Around the magnetron The waveguide MEASUREMENT WITH A FULLY ASSEMBLED OVEN After all components including the outer case are fully assembled measure for microwave energy leakage around the door viewing window the exhaust open...

Page 14: ...ACES ARE VERY HOT BEFORE SERVICING COOL DOWN THE TOASTER PARTS ENOUGH NOT TO GET BURNT 1 Open the door 2 Remove 2 screws holding the toaster 3 Disconnect the 2 lead wires from connectors CN2 CN3 4 Disconnect the wires at the secondary interlock switch and wires at the toaster door switch 5 Disconnect the wires from the toaster thermostat and wires at the Toaster Assembly 6 Lift up and pull out Toa...

Page 15: ...ally 2 After replacing the door check for microwave energy leakage with a survey meter Microwave energy must be below the limit of 5 mW cm sq with a 275 ml water load 3 When mounting the door assembly to the oven assembly be sure to adjust the door assembly parallel to the chassis Also adjust so the door has no play between the inner door surface and oven frame assembly If the door assembly is not...

Page 16: ...agnetron To prevent microwave leakage tighten the mounting screws properly making sure there is no gap between the waveguide and the magnetron E REMOVING THE TURNTABLE MOTOR Figure 11 1 Remove the turntable and rotating ring 2 Lay the unit down on its back 3 Remove the turntable motor cover The turntable base cover is easily removed by pinching the eight parts with a wire cutting 4 Disconnect the ...

Page 17: ...CHANISM The door lock mechanism is a device which has been specially designed to eliminate completely microwave activity when the door is opened during cooking and thus to prevent the danger resulting from the microwave leakage 2 MOUNTING OF THE PRIMARY MONITOR SECONDARY SWITCHES TO THE LATCH BOARD 3 INSTALLATION AND ADJUSTMENT OF THE LATCH BOARD TO THE OVEN ASSEMBLY Mount the latch board to the o...

Page 18: ... should indicate an closed circuit When the secondary switch operation is abnormal make the necessary adjustment or replace the switch only with the same type of switch C MONITOR SWITCH TEST Disconnect the wire lead from the monitor switch Connect the ohmmeter leads to the common COM and normally closed NC terminals of the switch The meter should indicate closed circuit in the door open condition ...

Page 19: ...IGH VOLTAGE TRANSFORMER Wire leads removed MAGNETRON Wire leads removed 1 Measure the resistance Select the ohm scale on the meter Primary winding Secondary winding Filament winding 2 Measure the resistance Select the ohm scale on the meter Primary winding to ground Filament winding to ground 1 Measure the resistance Select the ohm scale on the meter Filament terminal 2 Measure the resistance Sele...

Page 20: ...l 1 Check DC 9V battery before performing tests 2 Select the DCV scale on the meter 3 Using the meter battery and jump wire connect the items as illustrated in figures Terminal to case Normal Approximately 9V Normal Approximately 0V or a value displayed in mV Will be seen NOTE When testing the magnetron be sure to install the magnetron gasket in the correct position and be sure that the gasket is ...

Page 21: ...tems as illustrated in Figure 14 b This has the positive side of the battery connected to the cathode of the diode 3 The diode should be forward biased therefore a voltage reading of approximately 4 7 VDC to 6 4 VDC will be read depending on meter battery strength etc Note If the meter leads were reversed a negative voltage of the same amount would be seen STEP 3 Test the diode for reverse biasing...

Page 22: ... 3 8 sec 14 sec 4 10 sec 12 sec 5 12 sec 10 sec 6 14 sec 8 sec 7 16 sec 6 sec 8 18 sec 4 sec 9 20 sec 2 sec 10 22 sec 0 sec Normal A Approximately 400 469 ohms B Approximately 60 80 ohms Abnormal Infinite Normal Approx 12 0 14 0 Kohms Abnormal Infinite or several ohm NOTE A MICROWAVE LEAKAGE TEST MUST ALWAYS BE PERFORMED WHEN THE UNIT IS SERVICED FOR ANY REASON MAKE SURE THE WIRE LEADS ARE IN THE ...

Page 23: ...r operation of the primary interlock secondary interlock switches and or the interlock monitor switch Malfunction of the high voltage transformer the high voltage capacitor including the diode the magnetron the blower motor or the circuit board PROBLEMS CAUSES NOTES If the fuse is blown by an improper switch operation replace the defective switches and the fuse at the same time After replacing the...

Page 24: ...ive RELAY or poor connection of relay Replace RELAY or correct the connection NO Microwave Oven NO YES NO NO YES YES PROBLEM A FAN motor and indicator light turn on without touching START key when the door is closed Remove the mate connector of I O CON from the circuit board does the unit still operate GOOD GOOD Replace the circuit board PROBLEM B FAN motor and indicator light turn on When the doo...

Page 25: ...e high voltage Systems the interlock switches the door sensing and the relay check good 2 The unit with a normal relay continuously operates 3 The buzzer does not sound or continues to sound 4 Some segments of one or more digits do not light up or they continue to light up or segments light when they should not 6 Wrong figures appear 7 The figures of all digits flicker 8 Some of the indicators do ...

Page 26: ... working on this panel to discharge any static charge built up in your body Micom model only CONDITION Toaster and Microwave oven does not work Inserting many plugs into one outlet and using them at the same time blown fuse or breaker Plug is not inserted tightly Output power is too low Low AC input voltage Food temperature is too low Using metallic ware and allowing it to touch the oven wall Spar...

Page 27: ...light does not turn on after setting cooking cycle 11 Display time of day does not reappear when cooking is finished CONDITION CHECK RESULT CAUSE REMEDY 1 No input can be programmed Continuity No continuity Defective PCB assembly Loose connection Replace PCB assembly Connect them tightly Check the conn ection between membrane key assembly and PCB assembly 2 Some inputs cannot be programmed 3 Displ...

Page 28: ...ry monitor switches and RELAY RY2 of P C B Assembly Check continuity of monitor switch with door closed Check continuity of primary switch with door opened Disconnect one side of the wire lead connected from transformer to the high voltage capacitor and operate the unit Replace fuse 2 Fuse does not blow No continuity Continuity No continuity Defective power supply cord Replace power supply cord De...

Page 29: ...ures set but microwave oven does not start cooking while desired program times are set and START pad is touched TROUBLE 4 Microwave oven seems to be operating but little heat is produced in oven load NOTE Simple test of power output conducted by heating one liter water for one min if available Minimum 8 5 C temperature rise is normal condition CONDITION CHECK RESULT CAUSE REMEDY Output is low Lowe...

Page 30: ... relay 2 and check continuity relay 2 Operate the unit Abnormal Defective high voltage capacitor Replace high voltage capacitor Normal Check high vol tage capacitor Abnormal Defective high voltage diode Replace high voltage diode Normal Check high vol tage diode Abnormal Defective magnetron Replace magnetron Check magnetron TROUBLE 5 No microwave oscillation even though oven lamp and fan motor run...

Page 31: ...k the continuity of heater Check the connection between CN3 connector and PCB assembly 2 F 2 code Attached Seperated 2 wire leads are shorted contact Apart 2 wire leads as far as possible Check the CN3 connector whether 2 wire leads are attached Defective PCB assembly Replace PCB assembly 3 HOT code Internal temperature is over 220 deg c Allow the toaster to cool down Automatically fan will blow f...

Page 32: ...INTERIOR PARTS OVEN CAVITY PARTS BASE PLATE PARTS LATCH BOARD PARTS DOOR PARTS TOASTER PARTS 6 1 EXPLODED VIEW INTRODUCTION ...

Page 33: ...6 2 13536A 13552A 13213A 13581A 14890A 14970A 14026A 15006A 268712 WTP004 23506A 13720D DOOR PARTS ...

Page 34: ...6 3 WTP004 268712 23506A CONTROLLER PARTS ...

Page 35: ...6 4 WTP013 35889A 34370T 36549S 33390G WTT010 WTT021 33052A 33112U OVEN CAVITY PARTS ...

Page 36: ...6 5 WSZ085 56912B 55262A 44510A 43500A 466001 466003 466001 43501A LATCH BOARD PARTS ...

Page 37: ...6 6 54810C WTT024 56930V 56324A 56201B 50CZZH 56851C WSZ002 WTT028 268711 WTT037 568771 WSZ002 56411A 50FZZA WTT028 54974S 55900A 56549F 56201A WSZ002 INTERIOR PARTS ...

Page 38: ...6 7 56170D 63303A WSZ002 WTT021 WTT028 647781 65006A 63302A WTT021 BASE PLATE PARTS ...

Page 39: ...T028 768771 WTT021 75264A 73808A 75026G 74830A 74510L 466001 73550D 73720D 74830A 73300A 749702 73390M 73550H 75026C 749703 749703 749321 749322 75993M 73213A 73552A 73572A 53550L 73740A 768711 759302 759301 753002 753003 753001 749701 TOASTER PARTS ...

Page 40: ...1266 4148 D91 4 7K R9 4148 4 7K R93 4148 4 7K R92 D93 D92 5V 5V 4148 4 7K R90 R123 R122 R121 R120 D90 2K 2K 2K 2K Q122 A1266 Q123 A1266 Q121 A1266 4 V Disp DP P51 R77 R76 42 4 28 27 R85 100K 5 R86 R87 R88 R89 Q07 C3202 ZD2 5 6V R07 1K D0 R118 R119 R117 R116 R115 R114 R113 R110 100 9 R112 R11 13 14 1 12 10 4 12 1 Q118 C105 10 Q119 C105 P02 P70 P71 P01 P00 P05 P03 P04 P07 P06 26 P67 CN1 3 96mm 2002 ...

Page 41: ...8 2 MAIN PRINTED CIRCUIT BOARD ...

Page 42: ...8 3 KEY PRINTED CIRCUIT BOARD ...

Page 43: ...P NO 3828W5S3131 April 2003 Printed in Korea ...

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