LG MB-4042G Service Manual Download Page 1

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MICROWAVE OVEN

SERVICE MANUAL

MODEL: MB-4042G

CAUTION

BEFORE SERVICING THE UNIT, READ THE SAFETY PRECAUTIONS IN THIS MANUAL.

Website http://biz.lgservice.com

Summary of Contents for MB-4042G

Page 1: ...MICROWAVE OVEN SERVICE MANUAL MODEL MB 4042G CAUTION BEFORE SERVICING THE UNIT READ THE SAFETY PRECAUTIONS IN THIS MANUAL Website http biz lgservice com ...

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 12 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: ...m 12 0 kg approx 13 2 kg approx Microwave Power for Variable Cooking Power level Max Full power throughout the cooking time Med High approx 80 of Full power Medium approx 60 of Full power Defrost approx 40 of Full power Low Warm approx 20 of Full power Owner s manual Glass tray Roller rest Grill rack 1 1 ITEM MODEL Power Requirement Power Output Microwave Frequency Magnetron Timer Outside Dimensio...

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: ...ICK DEFROST Used to defrost quickly 1Lb 7 START Q START To quickly set the cooking time directly 8 MICRO Used to select the desired power level for cooking 9 CLOCK Used to set the time of day 10 MORE LESS Used to change the cooking time desired weight 11 STOP CLEAR Used to stop oven and clear all entries except time of day Oven Front Plate Window Door Screen Door Seal Display Window Control Panel ...

Page 8: ...KING 6 COMBINATION COOKING 7 AUTO WEIGHT DEFROST 8 CHILD LOCK This oven has a CHILD LOCK feature TO SET CHILD LOCK TO CANCEL CHILD LOCK 9 AUTO COOK Stop Clear Set clock Set the correct time Stop Clear Start Stop Clear Desired auto cook category Desired cooking weight Stop Clear Stop Clear Touch and Hold Stop Clear Stop Clear Touch and Hold STOP CLEAR Set clock Stop Clear Desired defrost category D...

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

Page 10: ...0 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 cut off pr...

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: ...re 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 minimize a...

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 THE TURNTABLE MOTOR REMOVAL 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 the...

Page 16: ...AND ADJUSTMENT OF THE LATCH BOARD TO THE OVEN ASSEMBLY Mount the latch board to the oven assembly Adjust the latch board in the arrow direction so that oven door will not have any play in it when the door is closed Tighten the mounting screw Check for play in the door by pushing the door release button Door movement should be less than 0 5 mm 1 64 inch Don t push the door release button while maki...

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 ...

Page 19: ...le Rx1000 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 Normal Abnormal Continuity NOTE When testing the magnetron be sure to install the magnetron gasket in the correct position and be sure that...

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: ...r 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 GRASP THE CONNECT...

Page 22: ...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 23: ... setting 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 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 24: ...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 25: ...ch 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 on and off time with mult...

Page 26: ... 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 27: ...function the 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 correc...

Page 28: ...INTERIOR PARTS OVEN CAVITY PARTS DOOR PARTS LATCH BOARD PARTS CONTROL PANEL PARTS BASE PLATE PARTS 6 1 EXPLODED VIEW INTRODUCTION ...

Page 29: ...6 2 13536A 13581A 14970A 14026A 13552A 13213A 14890A 13720D DOOR PARTS ...

Page 30: ...6 3 23506A 23572A 268711 WTT028 24781M CONTROL PANEL PARTS ...

Page 31: ...6 4 WTT010 WTT021 WTT021 33112U 33550H 35264A 33052M WTP013 35300S 33390G 36549S 948502 35889A 35026G WNZ015 WSZ184 OVEN CAVITY PARTS ...

Page 32: ...6 5 466001 43500A 44510A 466001 WSZ085 466003 LATCH BOARD PARTS ...

Page 33: ...6 6 56411A 568771 56930V 50FZZA 56201A 55900A WTT037 56549F WSZ002 WSZ002 WSZ062 WTT021 33808A 54974S WSZ002 WTT028 56851D 50CZZH 948501 54810C 56912B 55262A 56324A WSZ002 34930W INTERIOR PARTS ...

Page 34: ...6 7 WTT021 63302A 63303A WSZ002 65006B 56170D BASE PLATE PARTS ...

Page 35: ...1A HEATER SHEATH R 35889A 5889W2A013E ROTATING RING ASSEMBLY R 36549S 6549W1S011B MOTOR CIRC SYNCHRONOUS R 6549W1S017A 43500A 3500W1A011A BOARD LATCH R 44510A 4510W3A012A LEVER R 466001 6600W1K001D SWITCH MICRO R 466003 6600W1K001C SWITCH MICRO R 50CZZH 0CZZW1H001Q CAPACITOR DRAWING HIGH VOLTAGE R 0CZZW1H004G 50FZZA 3B70856U FUSE DRAWING R 54810C 4810W1A009B BRACKET CAPACITOR R 54974S 4974W1A001B ...

Page 36: ...G R WSZ184 1SZZW2Z001E SCREW DRAWING R WTP013 1TPL0402418 SCREW TAPPING PAN HEAD R WTT010 1TTG0402422 SCREW TAPPING TRUSS HEAD R WTT021 1TTL0402418 SCREW TAPPING TRUSS HEAD R WTT028 1TTL0402818 SCREW TAPPING TRUSS HEAD R WTT037 1TTL0403818 SCREW TAPPING TRUSS HEAD R 7 2 PART NO DESCRIPTION SVC ALTER R SERVICE PARTS NO ...

Page 37: ...8 1 SCHEMATIC DIAGRAM OF P C B ...

Page 38: ...8 2 PRINTED CIRCUIT BOARD ...

Page 39: ...ZW5A01C LED WAICHIWD061A 01BKGREEN100 R PT1 6170W1G010H TRANSFORMER POWER 220 240V50 60HZ12VLGECWMS 197W COMMON LED R Q07 0TR320209BA TRANSISTOR BIPOLARS KECKTC3202 OTPTO9250V150MA R Q120 0TR126609AA TRANSISTOR BIPOLARS KTA1266 Y KTA1015 KECTPTO9250V150MA R Q121 0TR126609AA TRANSISTOR BIPOLARS KTA1266 Y KTA1015 KECTPTO9250V150MA R Q122 0TR126609AA TRANSISTOR BIPOLARS KTA1266 Y KTA1015 KECTPTO9250V...

Page 40: ...89 0RD4702G608 RESISTOR FIXEDCARBONFILM 47KOHM1 4W5 TA26 R R90 0RD4701F608 RESISTOR FIXEDCARBONFILM 4 7KOHM1 6W5 TA26 R R91 0RD4701F608 RESISTOR FIXEDCARBONFILM 4 7KOHM1 6W5 TA26 R R92 0RD4701F608 RESISTOR FIXEDCARBONFILM 4 7KOHM1 6W5 TA26 R R93 0RD4701F608 RESISTOR FIXEDCARBONFILM 4 7KOHM1 6W5 TA26 R RY1 6920W2D010A RELAY OJ SS 112LMOEG250VAC3A12VDC1A R RY2 6920W5A012A RELAY G5G 1A DT1 LGOMRON250...

Page 41: ...P NO 3828W5S3284 June 2003 Printed in Korea ...

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