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LG MC-7642W, Service Manual, Page: 4 / 37

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LG MC-7642W Service Manual Download Page 4

This microwave oven is designed for household use only.

It is not recommended for commercial purposes.

DESCRIPTION

MC-7642W

230 Volts AC 50 Hz

Single phase, 3 wire grounded

Microwave

1,300W 

Grill

1,250W 

Combination

2,600W 

Convection

1,350W (Max. 2550W)

900 Watts full microwave power (IEC60705)

2,450 MHz

2M214 - 39F, 2M218J

0 ~ 90 min. 

512 (W) x 302 (H) x 500 (D) mm

342 (W) x 215 (H) x 338 (D) mm

22.0 kg   

23.5 kg

Microwave Power for Variable Cooking

Power level

MAX (900W)  ...................................... Full power throughout the cooking time

MED.-HIGH (720W) ............................ approx. 80% of Full power

MEDIUM (540W) ................................ approx. 60% of Full power

DEFROST (360W) .............................. approx. 40% of Full power

LOW/WARM (180W)........................... approx. 20% of Full power

• CONVECTION ..................................Max 250˚C

• GRILL

• COMBINATION

Owner's manual 

Glass turntable 

Rotating ring

Grill rack, Convection rack 

Metal tray

1-1

ITEM

MODEL

Power Requirement

Power Output

Microwave Frequency

Magnetron

Timer

Outside Dimensions

Cavity Dimensions

Net Weight

Shipping weight

Control Complement

Nameplate Location

Accessories

SPECIFICATIONS

Back side

Summary of Contents for MC-7642W

Page 1: ...MICROWAVE OVEN SERVICE MANUAL MODEL MC 7642W CAUTION BEFORE SERVICING THE UNIT READ THE SAFETY PRECAUTIONS IN THIS MANUAL ...

Page 2: ...r 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 defective or misadjusted components in the interlock monitor door seal...

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 13 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: ... Microwave Power for Variable Cooking Power level MAX 900W Full power throughout the cooking time MED HIGH 720W approx 80 of Full power MEDIUM 540W approx 60 of Full power DEFROST 360W approx 40 of Full power LOW WARM 180W approx 20 of Full power CONVECTION Max 250 C GRILL COMBINATION Owner s manual Glass turntable Rotating ring Grill rack Convection rack Metal tray 1 1 ITEM MODEL Power Requiremen...

Page 5: ...tron 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 from danger in ordinary use extreme care should be taken du...

Page 6: ...to prevent interference 8 Do not touch the front glass during or after cooking of the Grill and Combination mode This glass is very hot during heater operating 9 Do not operate the oven at microwave and combination mode with Grill rack placed in the cavity when the oven is empty EARTHING INSTRUCTIONS This microwave oven is designed to be used in a fully earthed condition It is imperative therefore...

Page 7: ...to weight defrost 7 STOP CLEAR Used to stop oven and clear all entries except time of day 8 START Q START One tap allows oven to begin functioning 9 COOK TIME Used to select cook time 10 MICRO Used to select the desired power level for cooking 11 GRILL Used to select the grill cooking 12 COMBI Used to select the combination cooking 13 CONVECTION Used to select the convection cooking 14 AUTO COOK U...

Page 8: ...cooking time Desired cooking time Start Stop Clear Stop Clear Touch and Hold Stop Clear Stop Clear Touch and Hold Stop Clear Start Stop Clear More Less Desired auto cook Stop Clear Stop Clear Function Combi Desired defrost category Food weight Start Stop Clear Desired Russian cook category Start Stop Clear Desired auto cook category Food weight Start Stop Clear Function Convection Desired convecti...

Page 9: ...SCHEMATIC DIAGRAM 4 3 ...

Page 10: ...ive 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 average output power of microwave oven as POWER LEVEL refer to page 1 1 One complete cycle of relay 2 is 22 seconds WHEN THE DOOR IS OPENED DURING COOKING Both the primary switch and relay 2 are cu...

Page 11: ...ich 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 radi...

Page 12: ...e test probe must be removed no faster than 1 inch sec 2 5 cm sec along the shaded area otherwise a false reading may result The test probe must be held with the grip portion of the handle A false reading may result if the operator s hand is between the handle and the probe When testing near a corner of the door keep the probe perpendicular to the surface making sure the probe horizontally along t...

Page 13: ...mperature is 5 K The microwave power output P in watts is calculated from the following formula P is measured while the microwave generator is operating at full power Magnetron filament heat up time is not included The water is stirred to equalize temperature throughout the vessel prior to measuring the final water temperature Stirring devices and measuring instruments are selected in order to min...

Page 14: ...ltage transformer and capacitor 3 Remove the screw holding the high voltage transformer to the baseplate F AIR DUCT ASSEMBLY REMOVAL 1 Disconnect the leadwire from lamp and MGT thermostat 2 Remove the mounting screw to the magnetron G MAGNETRON REMOVAL 1 Disconnect the leadwire from the high voltage transformer and high voltage capacitor 2 Carefully remove the mounting screws holding the magnetron...

Page 15: ...ltage diode earth screw 4 Remove the screw holding the high voltage capacitor bracket J REMOVING THE TURNTABLE MOTOR 1 Remove the turntable 2 Remove the turntable shaft VERY CAREFULLY with a slotted screwdriver 3 Lay the unit down on its back 4 Remove the turntable motor cover The turntable base cover is easily removed by pinching the six parts with a wire cutting 5 Disconnect the leadwire from th...

Page 16: ... 2 Remove screws which hold the PCB SUB ASS Y to the control panel 3 Disconnect the flat cable from the PCB SUB ASS Y and take off the PCB SUB ASS Y M INTERLOCK SYSTEM 1 INTERLOCK MECHANISM 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 microwav...

Page 17: ... closed meter 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 op...

Page 18: ...RESULTS HIGH VOLTAGE TRANSFORMER Wire leads removed MAGNETRON Wire leads removed 1 Measure the resistance Ohm meter scale Rx1 and Rx100 Primary winding Secondary winding Filament winding 2 Measure the resistance Ohm meter scale Rx1000 Primary winding to ground Filament winding to ground 1 Measure the resistance Ohm meter scale Rx1 Filament terminal 2 Measure the resistance Ohm meter scale Rx1000 F...

Page 19: ... Terminal to case Measure the continuity Forward Ohm meter scale Rx10000 Measure the continuity Reverse Ohm meter scale Rx10000 Normal Momentarily indicates several ohms and then gradually returns to infinite Normal Infinite Normal Continuity Abnormal Infinite Normal Infinite Abnormal Continuity NOTE When testing the magnetron be sure to install the magnetron gasket in the correct position and be ...

Page 20: ...e If the fuse is blown by improper switch operation replace the defective switch and the fuse at the same time Replace just the fuse if the switches operate normally NOTE Make sure heater is fully cooled when tested Measure the resistance Multi meter scale Rx1 Normal Grill heater Approx 42 ohm at 20 30o C Normal more than 0 5 Mohm Normal Abnormal Measure the resistance with 500V 100M ohm insulatio...

Page 21: ...ance Ohm meter scale R x 1 Measure the resistance Ohm meter scale R x 1000 Normal Approx 200 400 ohm Abnormal Infinite or several ohm Normal Approx 10 20 kohm 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 CORRECT POSITION WHEN REMOVING THE WIRE LEADS FROM THE PARTS BE SURE TO GRAS...

Page 22: ... Check continuity between switch terminals by pressing an appropriate pad on key board The contacts assignment of the respective pads on the key board is as shown left figures NOTE A MICROWAVE ENERGY LEAKAGE TEST MUST ALWAYS BE PERFORMED WHEN THE UNIT IS SERVICED FOR ANY REASON MAKE SURE THE WIRE LEADS ARE CORRECT POSITION WHEN REMOVING THE WIRE LEAD FROM THE PARTS BE SURE TO GRASP THE CONNECTOR N...

Page 23: ...el to discharge any static charge built up in your body CONDITION Microwave oven does not work Inserting many plug into one plug outlet and using them at the same time causes overloading Microwave oven 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 Sparks occurring Inconsistent intensi...

Page 24: ...ing cooking cycle 11 Display time of day does not reappear when cooking is finished 12 Beep sound is not heard when correct key is touched 5 14 TROUBLE 1 The following visual conditions indicate a probable defective control circuit CONDITION CHECK RESULT CAUSE REMEDY 1 No input can be programmed Continuity No continuity Defective PCB assembly Loose connection Replace PCB assembly Connect them tigh...

Page 25: ...ch 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 TROUBLE 2 Oven does not operate at all Display window does not display any figures and no input is accepted NOTE All these switches must be replaced at the same time Refer to page 5 6 5 7 2 Fuse does ...

Page 26: ...ntinuity of secondary switch with door closed Check fan motor Check oven lamp Abnormal Abnormal Normal Defective fan motor Defective fan motor Replace fan motor Replace fan motor Loose connection Connection then tightly CONDITION CHECK RESULT CAUSE REMEDY Output is low Lower than 90 of rating voltage Normal Abnormal Abnormal Measure the output power Disconnect the wire leads from relay 2 and check...

Page 27: ... Defective high voltage transformer Replace high voltage transformer Check H V transformer normal normal Abnormal Defective high voltage Diode Replace high voltage Diode Check H V diode Abnormal Defective high voltage capacitor Replace high voltage capacitor Check H V capacitor Abnormal Defective magnetron Replace magnetron Check Magnetron TROUBLE 5 No microwave oscillation even though oven lamp a...

Page 28: ...e heater Replace Replace TROUBLE 6 Oven does not cook properly when programmed for the set power level Operates properly on HIGH CONDITION CHECK RESULT CAUSE REMEDY Output is full when you set lower power level Abnormal Disconnect the wire leads from relay 2 and check continuity relay 2 Operate the unit Defective P C B assembly Replace P C B assembly NOTE Make sure the wore leads correct position ...

Page 29: ...INTERIOR PARTS OVEN CAVITY PARTS DOOR PARTS LATCH BOARD PARTS CONTROL PANEL PARTS BASE PLATE PARTS 6 1 EXPLODED VIEW INTRODUCTION ...

Page 30: ...6 2 13581A 14970A 14026A 13552A 13213A 14890A 13720D 15006A DOOR PARTS ...

Page 31: ...6 3 WTP015 26638A 23572A 24781M 268711 CONTROL PANEL PARTS ...

Page 32: ...6 4 WTT010 WTT021 33112U WTP013 36549S 33052M WSZ094 35300S WSZ184 WTT021 35264A 33550H 33390G 33390M 35026G 35026C 35889A 34370T WNZ015 OVEN CAVITY PARTS ...

Page 33: ...6 5 466001 43500A 44510A 466001 43501A WSZ085 466003 LATCH BOARD PARTS ...

Page 34: ... 55900A 56324A 54810C WTT028 50CZZH 50FZZA WSZ002 WTP004 56912B 56930M WSZ002 34930W 55262A 948501 WSZ002 56851D 56201A 55900N 53504A 54810S WNH002 56322A 53300G WTT022 WTT010 36549C WNH003 WWP008 WWS005 33808A 55300S 56208A 55900C WTT021 54350S 948502 WMT002 INTERIOR PARTS ...

Page 35: ...6 7 WTT021 63302A 63303A 56170D WSZ002 WTT028 647781 BASE PLATE PARTS ...

Page 36: ...8 1 SCHEMATIC DIAGRAM OF P C B ...

Page 37: ...8 2 PRINTED CIRCUIT BOARD ...

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