LG MH-655T Service Manual Download Page 27

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5-17

(TROUBLE 7) Grill

CONDITION

CHECK

RESULT

CAUSE

REMEDY

1. Heater is not

operating.

Abnormal.

Normal.

Heater.

Thermostat and
relay3.(Grill)

Abnormal.

Malfunction the
thermostat.

Malfunction the
heater.

Replace.

Wire connection.

No continuity.

Open or loosen.

Replace or
connect tightly.

Replace.

1. Lower tempera-

ture the oven.

Abnormal.

Normal.

Heater.

Thermostat and
relay3.(Grill)

Abnormal.

Malfunction the
thermostat.

Malfunction the
heater.

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 correct position.

* When removing the wire leads from 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.

Summary of Contents for MH-655T

Page 1: ...MICROWAVE OVEN SERVICE MANUAL MODEL MH 655T 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 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: ... kg approx 14 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 Grill COMBI Owner s manual Cooking guide Glass turntable Rotating ring Grill rack 1 1 ITEM MODEL Power Requirement Power Output Microwave Frequency Magnetr...

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: ... select grill cooking 5 AUTO COOK Used to cook the foods listed by one touch 6 AUTO DEFROST Used to select the auto weight defrost 7 STOP CLEAR Used to stop over and clear all entries except time of day 8 START One tap allows over to begin functioning Rotating Ring Grill Rack Oven Front Plate Window Door Screen Door Seal Control Panel Safety Door Lock System Turntable 10 min 1 min 10 sec Auto 1 2 ...

Page 8: ...OOK 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 10 GUIDE OPTION GUIDE OPTION Stop Clock Set the hour by touching DIAL Set the minute Start Stop Start STOP Start Stop Desired defrost category Desired cooking time Start Stop Desired auto roast cook category Desire...

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

Page 10: ...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 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: ...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: ...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: ...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 16: ...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 17: ...osed 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 open ...

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

Page 21: ...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 22: ...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 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: ...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 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: ...DOOR PARTS LATCH BOARD PARTS CONTROL PANEL PARTS INTERIOR PARTS BASE PLATE PARTS OVEN CAVITY PARTS 6 1 EXPLODED VIEW INTRODUCTION ...

Page 29: ...6 2 13581A 15006A 13552A 13213A 13352A 13720D 13650A 14970A 14026A DOOR PARTS ...

Page 30: ...6 3 24781S 268711 268712 WTP015 250202 23572A 250201 23806C 250204 250203 250205 CONTROL PANEL PARTS ...

Page 31: ...6 4 36549S 34036W 33112U WTT021 33808A WTT010 WSZ092 WTP013 WSZ184 WTT021 33052M 33390G 34370T 35264A 33550H 35300S 35026G 35889A OVEN CAVITY PARTS ...

Page 32: ...6 5 466001 43500A 44510A 466001 43501A 466003 LATCH BOARD PARTS ...

Page 33: ...6 6 55262A 56201A 56912B 50CZZH 568771 50FZZA 55900A 56549F 56930M 56411A WTT028 WSZ062 WSZ002 WSZ002 WTT028 WTT037 WSZ002 54810C 56851D 56851C 54974S 56201B 56324A INTERIOR PARTS ...

Page 34: ...6 7 63303A 63302A WTT021 WSZ062 WTT030 647781 56170D BASE PLATE PARTS ...

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

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

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LG MH-655T, Service Manual

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