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LG MH-657PLM, Service Manual

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LG MH-657PLM Service Manual Download Page 19

5-8

CAUTIONS

1. DISCONNECT THE POWER SUPPLY CORD FROM THE OUTLET WHENEVER REMOVING THE

OUTER CASE FROM THE UNIT. PROCEED WITH THE TEST ONLY AFTER DISCHARGING THE HIGH
VOLTAGE CAPACITOR AND REMOVING THE WIRE LEADS FROM THE PRIMARY WINDING OF THE
HIGH VOLTAGE TRANSFORMER. (SEE PAGE 2-1)

2. ALL OPERATIONAL CHECKS WITH MICROWAVE ENERGY MUST BE DONE WITH A LOAD (1 LITER

OF WATER IN CONTAINER) IN THE OVEN.

COMPONENTS

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.

(Ohm-meter scale: Rx1000)
• Filament to chassis

Approx.: 1.4 ohm
Approx.: 90 ohm
Less than: 1 ohm

Normal: Infinite
Normal: Infinite

Normal: Less than 1 ohm

Normal: Infinite

FILAMENT 
WINDING
TERMINAL

SECONDARY  
WINDING

PRIMARY  
TERMINAL

COMPONENT TEST PROCEDURE

Summary of Contents for MH-657PLM

Page 1: ...MICROWAVE OVEN SERVICE MANUAL MODEL MH 657PLM 658PMS CAUTION BEFORE SERVICING THE UNIT READ THE SAFETY PRECAUTIONS IN THIS MANUAL ...

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 5 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: ... 19 kg approx Microwave Power for Variable Cooking Power level MAX Full power throughout the cooking time 900W MED HIGH approx 80 of Full power 720W MEDIUM approx 60 of Full power 540W DEFROST approx 40 of Full power 360W LOW WARM approx 20 of Full power 180W Grill COMBI Owner s manual Cook book Glass turntable Rotating ring Cook tray 1 1 ITEM MODEL Power Requirement Power Output Microwave Frequen...

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: ...EIGHT Used to select the desired weight SET CLOCK Used to set the time of day 3 AUTO DEFROST Used to select the auto weight defrost 4 QUICK DEFROST Used to select the quick defrost 5 TEMPERATURE 6 MEMORY COOK Used to memory key for favorite cook 7 POWER Used to select the desired power level for cooking GRILL Used to select the grill cooking 8 COMBI Used to select the combination cooking 9 START O...

Page 8: ...he time of day 3 AUTO DEFROST Used to select the auto weight defrost 4 QUICK DEFROST Used to select the quick defrost 5 TEMPERATURE 6 MEMORY COOK Used to memory key for favorite cook 7 POWER Used to select the desired power level for cooking GRILL Used to select the grill cooking 8 COMBI Used to select the combination cooking 9 START One tap allows oven to begin functioning 10 STOP CLEAR Used to s...

Page 9: ...time The cooking time will increase by 1 second for each turn of the dial 10 QUICK DEFROST 11 TEMPERATURE SETTING 12 MEMORY SETTING To restore your favorite cook when you cook use it by pressing the favorite cook key Press MEMORY 1 button FA 1 appears on the display Turn DIAL knob to decrease cooking time The cooking time will decrease by 1 second for each turn of the dial Stop Start STOP Stop Des...

Page 10: ...SCHEMATIC DIAGRAM 4 4 ...

Page 11: ...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 12: ...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 13: ...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 14: ...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 15: ...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 16: ...ter 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 with a slotted screwdriver 3 Lay the unit down on its back 4 Remove the turntable motor cover The tu...

Page 17: ...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 making a...

Page 18: ... 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 19: ... 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 20: ... 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 21: ...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 38 ohm at 20 30o C Normal more than 0 5 Mohm Normal Abnormal Measure the resistance with 500V 1...

Page 22: ...esistance Ohm meter 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...

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 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 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: ...ntinuity 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 Abnormal Abnormal Measure the output power Disconnect the wire leads from relay 2 and check...

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

Page 30: ...6 2 13581A 13213A 14890A 13552A 13536A 14026A 14970A WTP004 15006A 13720D 13550A 136501 136502 DOOR PARTS ...

Page 31: ...6 3 26638A 23550A 23806C 24781S 250201 23572A 268712 249401 268711 CONTROL PANEL PARTS ...

Page 32: ... 4 33112U 33808A WTT021 WTT028 WTT021 33052M WSZ094 WTT020 35300S 36549S WTP013 348102 344701 344702 466003 348102 346810 568771 33390G 34370T 35889A 36549H 33390P 34810A 343501 34036W OVEN CAVITY PARTS ...

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

Page 34: ...324A 968101 56912B 55262A 50CZZH WSZ002 54810C 56851D WSZ002 WSZ002 WSZ002 56930M WTP004 WTT028 WTT028 56549F 50FZZA WTT037 568771 WSZ002 56201A WTT021 24970A 343502 WTT021 34810H 33550H 34930W 54975G WTP004 56322V INTERIOR PARTS ...

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

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