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SCHEMATIC DIAGRAM

4-3

IMPORTANT SAFETY NOTE: THE SHADED AREAS ON THIS SCHEMATIC DIAGRAM INCORPORATE SPECIAL FEATURES

IMPORTANT FOR PROTECTION FROM MICROWAVE RADIATION, FIRE,

ELECTRICAL SHOCK, AND

HAZARDS. WHEN SERVICING IT IS ESSENTIAL THAT ONLY MANUFACTURER'S SPECIFIED PA

RTS

BE USED FOR THE CRITICAL COMPONENTS IN THE SHADED AREAS OF THE SCHEMATIC DIAG

RAM.

NOTICE: SINCE THIS IS BASIC SCHEMATIC DIAGRAM, THE VALUES OF COMPONENTS AND

SOME PARTIAL CONNECTIONS ARE SUBJECT TO CHANGE FOR IMPROVEMENT.

PRIMARY

SWITCH

THERMOSTAT

MAGNETRON

H.V.

CAPACITOR

H.V. DIODE

FUSE

15A

AC 120V

60Hz

MICOM

CONTROLLER

F.M.

TRANSFORMER

H.V.

** NOTE : DOOR IS OPENED.

BK : BLACK BL : BLUE YL : YELLOW

RD : RED WH : WHITE PK : PINK

GN : GREEN

O.L.

CN1

PT1

SECONDARY

SWITCH

OVEN

LAMP

MONITOR

SWITCH

TURN

TABLE

MOTOR

FAN

MO TOR

RY1

RY2

T.T.M.

Summary of Contents for MS-74ML

Page 1: ...MICROWAVE OVEN SERVICE MANUAL MODEL MS 74ML CAUTION BEFORE SERVICING THE UNIT READ THE SAFETY PRECAUTIONS IN THIS MANUAL Jan 2000 Printed in Korea P NO 3828W5S1403 website http biz lgservice com ...

Page 2: ...nd 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 defective or misadjusted components in t...

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: ... phase 3 wire grounded 700 Watts full microwave power IEC705 2 450 MHz 2M214 39F 2M218J 2M254J 0 99 min 90 sec 483 W x 285 H x 360 D mm 312 W x 198 H x 316 D mm 12 5 kg approx 14 kg approx 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 Defro...

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: ...lat 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 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 wire...

Page 7: ... oven to begin functioning 8 STOP CLEAR Used to stop oven and clear all entries except time of day 9 DISPLAY WINDOW 10 KITCHEN TIMER 4 1 OPERATING INSTRUCTIONS Oven Frot Plate Window Door Screen Door Seal Display Window Control Panel Safety Door Lock System Turntable Rotating Ring Reloj Tiempo Cocción Automática 10 min 1 min 10 seg 0 1kg 1kg Papas Vegetales Frescos Vegetales egetales Congelados Co...

Page 8: ...CROWAVE COOKING 5 MULTI STAGE MICROWAVE COOKING 6 AUTO WEIGHT DEFROST COOKING 7 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 8 AUTO COOK 4 2 Stop Set clock Set the correct time Stop Start Stop Desired auto cook category STOP STAGE 1 Set clock Stop Stop Desired defr...

Page 9: ...THE SCHEMATIC DIAGRAM NOTICE SINCE THIS IS BASIC SCHEMATIC DIAGRAM THE VALUES OF COMPONENTS AND SOME PARTIAL CONNECTIONS ARE SUBJECT TO CHANGE FOR IMPROVEMENT RD BK PRIMARY SWITCH WH THERMOSTAT WH WH YL MAGNETRON RD RD H V CAPACITOR H V DIODE FUSE 15A AC 120V 60Hz BL L N MICOM CONTROLLER F M TRANSFORMER H V NOTE DOOR IS OPENED BK BLACK BL BLUE YL YELLOW RD RED WH WHITE PK PINK GN GREEN O L CN1 PT1...

Page 10: ...ximately 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 a...

Page 11: ...ity of the microwave radiation leakage emitted by the microwave oven should not exceed 5 mW cm2 Always start measuring of an unknown field to assure safety for operating personnel from radiation leakage NECESSARY MEASURING INSTRUMENTS TESTER VOLTS DC AC Ohmmeter Microwave survey meter Holaday HI 1500 HI 1501 Narda 8100 8200 Inch scale 600 cc non conductive material beaker glass or plastic inside d...

Page 12: ...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 the oven surface this may possibly cause...

Page 13: ...nal 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 d...

Page 14: ... 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 suction guide ASS ...

Page 15: ... 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 motor cover The turntable ba...

Page 16: ...Y 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 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 ...

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: ...TS TEST PROCEDURE 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 Between Filament terminal 2 Measure the resistance Ohm mete...

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 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 the gask...

Page 20: ...EL 20 6 sec 16 sec 40 10 sec 12 sec 60 14 sec 8 sec 80 18 sec 4 sec 100 22 sec 0 sec Normal A B Approx 65 80 ohm B C Approx 10 30 ohm A C Approx 85 105 ohm Abnormal Infinite or several ohm Normal Approx 2 4 KΩ Abnormal or several Ω 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 W...

Page 21: ...static charge built up in your body Micom model only CONDITION Microwave oven does not work Inserting many plug into one plug 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 Inconsistent intensity o...

Page 22: ...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 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 tigh...

Page 23: ...f 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 Defective thermostat Replace thermost...

Page 24: ...ws 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 ...

Page 25: ... unit Check high vol tage transformer Abnormal Defective circuit protector Replace circuit protector Normal Check circuit protector 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 magnetr...

Page 26: ...unit NOTE Make sure the wire leads correct position When Removing the wire leads from the parts be sure to grasp the connector not the wires When removing the magnetron be sure to install the magnetron gasket in the correct position and in good condition CONDITION CHECK RESULT CAUSE REMEDY TROUBLE 5 No microwave oscillation even though oven lamp and fan motor run Display operates properly ...

Page 27: ...DOOR PARTS LATCH BOARD PARTS CONTROL PANEL PARTS INTERIOR PARTS BASE PLATE PARTS OVEN CAVITY PARTS 6 1 EXPLODED VIEW INTRODUCTION EV MODEL MS 74ML ...

Page 28: ...6 2 14970A 14026A 13552A 13536A 13213A 13720D 13352A 13581A DOOR PARTS EV ...

Page 29: ...6 3 WTP018 26638A 23572A 23550D 24930D 24781M 268711 CONTROL PANEL PARTS EV ...

Page 30: ...6 4 33112U WTT021 36549S WTP013 33052M 33390G 35889A OVEN CAVITY PARTS EV ...

Page 31: ...6 5 43501A 43500A 466001 WSZ085 466003 466002 44510A LATCH BOARD PARTS EV ...

Page 32: ...6 6 WSZ002 WSZ002 WTT028 WSZ062 WSZ002 WTT037 56324A 55262A 55900A 56549F 56411A 56930V 568771 54974S 56912B INTERIOR PARTS EV ...

Page 33: ...6 7 BASE PLATE PARTS 63303A 63302A WTT021 65006B 65006B WSZ002 56851D 54810C 50CZZH 56170D WSZ002 EV ...

Page 34: ...8 1 SCHEMATIC DIAGRAM OF P C B ...

Page 35: ...8 2 PRINTED CIRCUIT BOARD ...

Page 36: ......

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