LG MB-387W Page 1 Service Manual Download

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MICROWAVE OVEN

SERVICE MANUAL

MODEL: MB-387W

CAUTION

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

Website: http://biz.lgservice.com

P/NO : 3828W5S2280

June, 2002

Printed in Korea

Summary of Contents for MB-387W

Page 1: ...MICROWAVE OVEN SERVICE MANUAL MODEL MB 387W CAUTION BEFORE SERVICING THE UNIT READ THE SAFETY PRECAUTIONS IN THIS MANUAL Website http biz lgservice com P NO 3828W5S2280 June 2002 Printed in Korea ...

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: ...2 W x 203 H x 293 D mm 13 kg approx 14 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 turntable Roller Rest Grill rack ITEM MODEL Power Requirement Power Output Microwave Frequency Magnetron Ti...

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: ...1 POWER Used to select the desired power level for cooking 2 AUTO COOK Used to cook the foods listed by one touch 3 INDICATORS 4 AUTO DEFROST Used to select the auto weight defrost 5 QUICK DEFROST Used to select the auto weight defrost 6 STOP CLEAR Used to stop over and clear all entries except time of day 7 CLOCK Used to set the time of day 8 START QUICK START One tap allows over to begin functio...

Page 8: ... the last item entered or to the clock 3 QUICK START 4 MICROWAVE COOKING 5 GRILL COOKING 6 COMBI COOKING 7 AUTO WEIGHT DEFROST 8 AUTO COOK 9 CHILD LOCK This oven has a CHILD LOCK feature TO SET CHILD LOCK Touch the pad Touch STOP pad L appear in the display TO CANCEL CHILD LOCK Touch the pad touch STOP pad L disappears Stop Clock Number Stop Start STOP Clock Stop Desired defrost category Number of...

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 WHEN THE DOOR IS OPENED DURING COOKING Both the primary switch and relay 2 are cut off primary winding voltage of the high vo...

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: ...al water temperature and the ambient temperature is 5 K The microwave power output P in watts is calculated from the following formula 4187 x T T is measured while the microwave generator is operating at full power Magnetron filament heat up time is not included about 3 sec The water is stirred to equalize temperature throughout the vessel prior to measuring the final water temperature Stirring de...

Page 14: ...ORMER REMOVAL 1 Discharge the high voltage capacitor 2 Disconnect the leadwire from magnetron high voltage transformer and capacitor 3 Remove the screw holding the high voltage transformer to the baseplate F FAN MOTOR ASSEMBLY REMOVAL 1 Discharge the high voltage capacitor 2 Disconnect the leadwire from fan motor noise filter and high voltage capacitor 3 Remove the two screws holding the the sucti...

Page 15: ... below the limit of 5 mW cm2 With a 275 ml water load Make sure that gasket is rigidly attached to the magnetron To prevent microwave leakage tighten the mounting screws properly making sure there is no gap between the waveguide and the magnetron J REMOVING THE TURNTABLE MOTOR 1 Remove the turntable 2 Remove the turntable shaft VERY CAREFULLY 3 Lay the unit down on its back 4 Remove the turntable ...

Page 16: ...STALLATION 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...

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: ...EDURE RESULTS HIGH VOLTAGE TRANSFORMER Wire leads removed MAGNETRON Wire leads removed 1 Measure the resistance Ohm meter scale Rx1 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 Filam...

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: ... 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 Check for continuity of the H V Fuse with multi meter NOTE Make sure heater is fully cooled when tested Measure the resistance Multi meter scale Rx1 Normal Grill heater Approx 38 ohm at 20 30oC Normal more than 0 5 Mohm Normal Abnormal Measure the...

Page 21: ...sure the resistance Ohm meter scale R x 1000 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 CONNECTOR NOT THE WIRES Cooking Start OFF 1 3 5 Relay 2 Relay 1 Relay 3 Cooking Start OFF A B C FAN MOTOR Wire leads removed TURNTABLE MOTOR ...

Page 22: ... 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 intensity of microwave by their characteristics 1 Wrap the thinner part with aluminum f...

Page 23: ...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 13 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: ...uity 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 Normal Abnormal Abnormal Measure the output power Disconnect the wire leads from relay 2 and ch...

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: ...LATCH BOARD PARTS INTERIOR PARTS BASE PLATE PARTS OVEN CAVITY PARTS DOOR PARTS CONTROL PANEL PARTS 6 1 EXPLODED VIEW INTRODUCTION MODEL MB 387W EV ...

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

Page 30: ...6 3 268711 24781S 23790D 23572A 250202 249402 249401 250201 250203 WTP004 CONTROL PANEL PARTS EV ...

Page 31: ...6 4 OVEN CAVITY PARTS WTT021 35264A 33112U 948502 WSZ131 33052M 35300S 36549S 33390G WTT020 WNZ015 WTT021 35026G 35889A WSZ228 WTP013 EV ...

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

Page 33: ... 6 INTERIOR PARTS 33808A 56201B 56930V WSZ002 56324A 34930W 55900A WSZ002 50FZZA 56201A WTT037 56549F 54974S 56851D WSZ002 56901A 54810C WSZ002 948501 55262A 568771 50CZZH 56912B WSZ062 56411A WTT021 EV ...

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

Page 35: ...8 1 SCHEMATIC DIAGRAM OF P C B ...

Page 36: ...8 2 PRINTED CIRCUIT BOARD ...

Page 37: ......

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