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LG MC-7684B, Service Manual

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LG MC-7684B 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 MC-7684B

Page 1: ...E OVEN SERVICE MANUAL MODEL MC 7684B MC 7684BS CAUTION BEFORE SERVICING THE UNIT READ THE SAFETY PRECAUTIONS IN THIS MANUAL Website http biz lgservice com P NO MFL37307701 November 2006 Printed in Korea 삼 흥 정 판 ...

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: ...TING SEQUENCE 4 2 SCHEMATIC DIAGRAM 4 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 CONTENTS ...

Page 4: ...8 D mm 21 0 kg 23 0 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 High rack Low rack Metal tray ITEM MODEL Power ...

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: ...IGHT DEFROST Used to select the auto weight defrost 7 QUICK DEFROST Used to defrost quickly 8 STOP CLEAR Used to stop oven and clear all entries except time of day 9 START Q START One tap allows oven to begin functioning 10 DIAL To select convection temperature change cooking time and weight 11 SPECIAL COOK Used to select the special cook Turntable Rotating Ring Oven Front Plate Window Door Screen...

Page 8: ...er return to the last item entered or to the clock 3 CHILD LOCK This oven has a CHILD LOCK feature TO SET CHILD LOCK Touch the Stop pad Touch STOP pad L appear in the display TO CANCEL CHILD LOCK Touch the Stop pad Touch STOP pad L disappears 4 QUICK START 5 MICROWAVE COOKING 6 AUTO WEIGHT DEFROST 7 AUTO COOK 8 SPECIAL COOK Stop Clock Clock Set the hour Set the minutes Clock Stop Power Start Quick...

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

Page 10: ...HE 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 primary winding voltage of the high voltage transformer ON OFF ...

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: ... deflection 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 is mov...

Page 13: ... temperature is 5 K The microwave power output P in watts is calculated from the following formula 4187 x T 0 55 X T2 T0 X M T T2 Temperature after heating T0 Temperature of bowl M Weight of bowl 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 t...

Page 14: ...voltage 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 magnetr...

Page 15: ...g 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 the turntable motor terminals 6 Remove the screw se...

Page 16: ...s page 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 microwave activity when the door is opened during cooking and thus to prevent the danger resulting from the microwave lea...

Page 17: ...it 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 closed meter sh...

Page 18: ...OMPONENTS TEST PROCEDURE 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...

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: ... replacing the fuse 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 ...

Page 21: ... Measure the resistance Ohm meter scale R x 1000 Check for P C B connector 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: ...DS ARE CORRECT POSITION WHEN REMOVING THE WIRE LEAD FROM THE PARTS BE SURE TO GRASP THE CONNECTOR NOT THE WIRES Relay 2 Relay 3 Relay 5 1 2 3 4 5 6 7 8 9 10 18 1 2 3 4 5 6 7 8 9 10 18 Key P C B Main P C B Cooking Start OFF CN2 1 3 4 5 9 6 8 Relay 6 Relay 4 24V BN COM YL 230V BL Cooking Start OFF Normal COM 230V Approx 150 Ω COM 24V Approx 20 Ω Abnormal Infinite or several ohm Check continuity betw...

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 Everything works as specified Continuity No continuity Still have trouble Defective key membrane assembly Defective PCB assembly Loo...

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: ...uity of secondary switch with door closed Check fan motor Check oven lamp Abnormal Abnormal Normal Defective fan motor Defective oven lamp Replace fan motor Replace oven lamp 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 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: ...on 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 are in the c...

Page 29: ...INTERIOR PARTS OVEN CAVITY PARTS DOOR PARTS LATCH BOARD PARTS CONTROL PANEL PARTS BASE PLATE PARTS 6 1 EXPLODED VIEW INTRODUCTION MODEL MC 7684B MC 7684BS EV ...

Page 30: ...6 2 15006A 13552A 14890A 13213A 13720D 14026A 14970A WTP018 13581A 13650A DOOR PARTS EV ...

Page 31: ...6 3 24781S 23572A 23790D 25020T 25020G 24940P 24940D 25020K 25020S 25020E 268711 WTP004 CONTROL PANEL PARTS EV ...

Page 32: ...6 4 WTT011 33052M 36549S 33390G 34370T 35889A 34810H 33112U WSZ002 44360A 34810H WSZ002 WTP013 WNH001 34810M WTT010 33390M 35026G 34980A 35026C 33550H 35300A 368771 OVEN CAVITY PARTS EV ...

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

Page 34: ...Z002 WSZ002 WTT028 WSZ002 50CZZH 56549F 54810C 56324A 55262A 948501 56912B 55900A WTT021 WNH002 55900N 348103 348102 535041 WSZ228 WTT029 54350S WWS005 WSZ228 56208A 55900C 348101 568772 55300S WSZ002 34930W 56930G 54974A WTT021 WTP004 56851D Button Head Torx style 2 WSZ185 INTERIOR PARTS EV ...

Page 35: ...6 7 63302A 56170D 63303A WSZ002 WTT021 647781 WTT030 BASE PLATE PARTS EV ...

Page 36: ......

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