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LG MS-3942FB, Service Manual

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LG MS-3942FB Service Manual Download Page 19

5-9

COMPONENTS

TEST PROCEDURE

RESULTS

HIGH VOLTAGE
CAPACITOR

HIGH VOLTAGE
DIODE

NOTE :
Some inexpensive meters
may indicate infinite
resistance in both direction.

Measure the resistance.
(Ohm-meter scale: Rx1000)
• Terminal to terminal.

Measure the resistance.
(Ohm-meter scale: 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: Infinite.

Normal: Infinite.
Abnormal: Continuity.

NOTE: When testing the magnetron, be sure to install the magnetron gasket

in the correct position and be sure that the gasket is in good condition.

Antenna

Gasket

Chassis

Filament

Summary of Contents for MS-3942FB

Page 1: ...MICROWAVE OVEN SERVICE MANUAL MODEL MS 3942FB CAUTION BEFORE SERVICING THE UNIT READ THESAFETY PRECAUTIONS IN THIS MANUAL website http www lgservice com ...

Page 2: ...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 the magnetron wave guide or transmission line and cavity for proper alignment integrity and connecti...

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: ...e phase 3 wire grounded 1 100 Watts full microwave power IEC705 2 450 MHz 2M248 0 99 min 99 sec 556 W x 321 H x 439 D 377 W x 251 H x 405 D 16 7 kg approx 18 3 kg approx Touch Control System Clock 1 00 12 59 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 Lo...

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: ...st 10 cm 4 inches from the wall 7 Place the microwave oven as far away as possible from TV RADIO COMPUTER etc to prevent interference EARTHING INSTRUCTIONS This microwave oven is designed to be used in a fully earthed condition It is imperative therefore to make sure it is properly earthed before servicing WARNING THIS APPLIANCE MUST BE EARTHED IMPORTANT As the colors of the wires in the mains lea...

Page 7: ... This feature provides you with the quick defrosting method for 0 5kg of beef 6 AUTO DEFROST This feature provides you with the best defrosting method for frozen foods 7 NUMBER These used to set for time of day cooking time power level or defrost weight 8 POWER You can select the desired power level for cooking 9 CLOCK It is used to set the time of day 10 STOP CLEAR It used to stop oven and clear ...

Page 8: ...UCH COOKING NOTE Heat only 1 package at a time 4 TIME COOKING 5 MULTI STAGE COOKING 6 AUTO DEFROST COOKING 7 CHILD LOCK This oven has a CHILD LOCK feature TO SET CHILD LOCK Touch the pad Touch and hold pad LOCK appear on the display TO CANCEL CHILD LOCK Touch and hold pad LOCK disappears 8 MORE LESS The cook time is adjustable by MORE pad or LESS pad STOP CLEAR CLOCK NUMBER STOP CLEAR PIZZA STOP C...

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

Page 10: ...pproximately 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 t...

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: ...on The 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 al...

Page 13: ... 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 devices and measuring instruments are selected in order t...

Page 14: ...TE 1 After replacing the door be sure to check that the primary switch monitor switch and secondary switch operate normally 2 After replacing the door check for microwave energy leakage with a survey meter Microwave energy must be below the limit of 4 mW cm 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 Al...

Page 15: ...etween the waveguide and the magnetron G REMOVING THE TURNTABLE MOTOR 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 leadwire from the turntable motor terminals 5 Remove the screw securing the turntable motor to the oven cavity ASS...

Page 16: ... 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 oven assembly Adjust the latch board in the arrow direction so that oven door will not have any play in it when ...

Page 17: ... 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 When the door is...

Page 18: ...LTS 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 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: ...ec 2 6 sec 16 sec 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 Approx 120 320 ohm B Approx 20 40 ohm Abnormal Infinite or several ohm Normal Approx 100 150 ohm Abnormal Infinite or several ohm Relay 2 A B NOTE A MICROWAVE LEAKAGE TEST MUST ALWAYS BE PERFORMED WHEN THE UNIT IS SERVICED FOR ANY REASON MAKE SURE TH...

Page 21: ... panel to discharge any static charge built up in your body Micom model only CONDITION Microwave oven does not work Inserting many plugs into one outlet and using them at the same time blown fuse or breaker 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 occur Inco...

Page 22: ... does not turn on after setting cooking cycle 11 Display time of day does not reappear when cooking is finished 5 12 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 tightly Check the conn ection b...

Page 23: ...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 Continuity Malfunction of secondary switch Replace fuse primary monitor secondary switches and RELAY RY2 of P C B Assembly No continuity Check continuity of secondary switch with door opened 2 Fuse does not blow No continuity Continuity ...

Page 24: ... all figures set but oven does not start cooking while desired program times are set and START pad is touched TROUBLE 4 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 Lower than 90 of...

Page 25: ... 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 Displ...

Page 26: ...INTERIOR PARTS OVEN CAVITY PARTS DOOR PARTS LATCH BOARD PARTS CONTROL PANEL PARTS BASE PLATE PARTS 6 1 EXPLODED VIEW INTRODUCTION ...

Page 27: ...6 2 13552A 13213A 13352A 13581A 14970A 14026A 13536A 15006A 13720D DOOR PARTS ...

Page 28: ...6 3 23506A 23572A 268711 WTP018 24781M 23550D CONTROLLER PARTS ...

Page 29: ...6 4 33390G WTT020 WTT010 WTT021 35889A 33052A 36549S WTP013 33112U OVEN CAVITY PARTS ...

Page 30: ...6 5 56912B 43500A 44510A 466003 466001 466001 55262A 43501A WSZ085 LATCH BOARD PARTS ...

Page 31: ...6 6 568771 WSZ002 WSZ002 WSZ002 WSZ002 WSZ002 WSZ196 56411A 56930V 56549F 54974S WTT037 55900A 56324A 948502 948503 54810C WTT028 50CZZH 34930W 50FZZA 56201A 56201B 56851D 56901A INTERIOR PARTS ...

Page 32: ...6 7 56170D WSZ002 WTT021 63302A 65006B 63303A 948501 BASE PLATE PARTS ...

Page 33: ...8 1 SCHEMATIC DIAGRAM OF P C B ...

Page 34: ...8 2 PRINTED CIRCUIT BOARD ...

Page 35: ...P NO 3828W5S1580 Aug 2000 Printed in Korea ...

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