LG MH-794GS Service Manual Download | Manualshive

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COMPONENTS

TEST PROCEDURE

RESULTS

CN2

1

3

5

7

Relay 1

Relay 4

Relay 2

Relay 3

3 2 1

BK

WH

RD

Shield wire

connector

1
2
3
4
5

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21
22
23
24

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1
2
3
4
5
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21
22
23
24

P.C.B

Tact S/W

Cooking Start

OFF

Cooking Start

OFF

Check continuity between
switch terminals, by pressing an
appropriate pad on key board.
The contacts assignment of the
respective pads on the key
board is as shown left figures.

Measure the resistance.

RELAY 1,4, OF P.C.B
(Disconnect the 7 pin
connector from P.C.B)
See Schematic Dagram on
page 11)
RY1 : Turn Table,

Fan Motor,
Oven Lamp

RY4 : Heater Moving Motor

RELAY 4, 5 OF P.C.B
(Wire leads removed.)
RY3 : Grill
RY2 : Microwave

KEY PAD

SENSOR

(Wire leads removed)

NOTE : A MICROWAVE ENERGY LEAKAGE TEST MUST ALWAYS BE PERFORMED WHEN THE UNIT IS

SERVICED FOR ANY REASON.
MAKE SURE THE WIRE LEADS ARE CORRECT POSITION.
WHEN REMOVING THE WIRE LEAD FROM THE PARTS, BE SURE TO GRASP THE
CONNECTOR, NOT THE WIRES.

Port

Resistance

1 and 2 Approx.1M

Ω

1 and 3 Approx.5K

Ω

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Summary of Contents for MH-794GS

Page 1: ...MICROWAVE GRILL OVEN SERVICE MANUAL MODEL MH 794GS CAUTION BEFORE SERVICING THE UNIT READ THE SAFETY PRECAUTIONS IN THIS MANUAL August 1999 P NO 3828W5S1308 Printed in Korea ...

Page 2: ...r 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 com partments 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 and microwave generation and t...

Page 3: ...12 SERVICE INFORMATION 13 TOOLS AND MEASURING INSTRUMENTS 13 MICROWAVE LEAKAGE TEST 13 MEASUREMENT OF MICROWAVE POWER OUTPUT 15 DISASSEMBLY AND ADJUSTMENT 15 INTERLOCK CONTINUITY TEST 20 COMPONENT TEST PROCEDURE 21 TROUBLE SHOOTING GUIDE 25 EXPLODED VIEW 31 REPLACEMENT PARTS LIST 38 MICOM CONTROLLER SCHEMATIC DIAGRAM 40 MICOM CONTROLLER P C B LAYOUT 41 TACT SWITCH BUTTON POSITION 42 MICOM CONTROLL...

Page 4: ...mm W X 235mm H X 406mm D Net Weight 17 5kg approx Shipping weight 19 5kg approx Control Complement Microwave Power for Variable Cooking Power level HIGH Full power throughout the cooking time 100 MED HIGH approx 80 of Full power MEDIUM approx 60 of Full power DEFROST approx 40 of Full power LOW approx 20 of Full power Grill Combination 1 2 3 Name plate Location Accessories Owner s manual Rotating ...

Page 5: ...e 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 CAUTIONS 5 Unlike other appliances the microwave oven is high voltage and high current appliance Though it is free from danger in ordinary use extreme care should be taken during rep...

Page 6: ...into a 15A outlet 9 Do not touch the front glass during or after cooking of the Grill Convection and Combination mode This glass is very hot during heater operating 10 Do not operate oven at microwave and combination mode with the Convection rack or 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 I...

Page 7: ... cooking mode NOTE A beep sounds when a button on the control panel is touched to indicate a setting has been entered DEF 1 To defrost SENSOR REHEAT MENUS Dinner Plate Chilled Meal Soup Sauce SENSOR COOK MENUS Potato Fresh Vegetable Frozen Vegetable Pasta Fresh Fish CLOCK KITCHEN TIMER Set the clock or timer DISPLAY INDICATOR Shows Time of Day Cooking power Level Cooking Category TEMPERATURE INDIC...

Page 8: ... move 5 French Fish Grill Cook Combination Cook French Fries Chicken Legs Grill heater will move to Grill heater will move the cooking position to the backside Grill heater will stay at the cooking position COOK CATEGORY Sensor Cook M W Sensor Reheat Grill heater will stay at the cooking position When the cook is ended the food must be removed When the cook is ended and you want to cook the next c...

Page 9: ...Cook Combi Cook Sensor Cook Auto Roast Cook DEF1 DEF2 2times Set the correct hour Set the correct minute Stop Clear Desired power level Set the correct minute Stop Clear Desired cooking time twice Stop Clear Desired cooking time 3 times Set Combi 1 2 or 3 Stop Clear Desired Sensor Cook Stop Clear Desired auto roast cook Desired food weight Stop Clear Set Defrost ...

Page 10: ...mme Desired Cooking Stop Clear Stop Clear Stop Clear Touch and Hold Stop Clear Stop Clear Touch and Hold Stop Clear Stop Clear Child Lock Quick Start More and Less Temp To Set CHILD LOCK L appears on the display and you can t input any key L disappears on the display To Cancel CHILD LOCK To Set MORE LESS ...

Page 11: ...SCHEMATIC DIAGRAM 11 ...

Page 12: ...agnetron WHEN THE OVEN IS SET AT ANY LEVEL EXCEPT MAXIMUM The micom controller controls the ON OFF time of relay 5 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 5 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 tran...

Page 13: ...ts in customer s home EQUIPMENT Microwave Survey Meter 600cc glass beaker Glass thermometer 100 C NECESSARY MEASURING INSTRUMENTS TESTER VOLTS DC AC Multmeter Microwave survey meter Holaday H1 1500 Hi 1501 Narda 8100 8200 Inch scale 600 cc non conductive material beaker glass or plastic inside diameter approx 8 5cm 31 2 in Cylindrical and made of borosilicate glass vessel max thickness 3mm outside...

Page 14: ... 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 th...

Page 15: ...final water tempera ture and the ambient temperature is 5 K A OUT CASE REMOVAL 1 Disconnect power supply cord from the outlet 2 Remove the screws from the rear and along side egges of the case The ouer case must be moved backward to the lifted off B POWER SUPPLY CORD 1 Remove the out case 2 Disconnect two terminals and remove one screw of the earth terminal CAUTION DISCHARGE THE HIGH VOLTAGE CAPAC...

Page 16: ...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 Y...

Page 17: ... 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 with a slotted hand 3 Lay the unit down on its back 4 Remove the turntable motor cover The tur...

Page 18: ...ty on the Right 2 Remove the H M MOTOR ASS Y 3 Remove the Washer 4 Remove the Gasket L Sensor ASS Y 1 Remove the Screw of the back and on the Cavity 2 Remove the Screw of the Bracket 3 Remove the Bracket 4 Remove the Screw of Sensor Case 5 Remove the Sensor PCB Ass y 18 Heater Gasket Joint Spring Cover Terminal Bracket Ass y Motor Ass y Bracket Washer Gasket Gear S W 1 H M Motor Ass y S W 2 ...

Page 19: ...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 the 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 5mm 1 64 inch Don t push the door release button while making adjustment Mak...

Page 20: ...s closed meter should indicate a closed circuit When the sec ondary switch operation is abnormal make the nec essary 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 NO terminals of the switch The meter should indicate closed circuit in the door ...

Page 21: ... TEST PROCEDURE RESULTS HIGH VOLTAGE TRANSFORMER Wire leads removed 1 Measure the resistance Multi meter scale R x 1 and R x 100 Primary winding Approx 2 Ω Secondary winding Approx 90 Ω Filament winding Less than 1 Ω 2 Measure the resistance Multi meter scale R x 1000 Primary winding to ground Normal Filament winding to ground Normal MAGNETRON 1 Measure the resistance Wire leads removed Multi mete...

Page 22: ...Rx1000 Terminal to termonal Normal Momentary indicates several ohms and then gradually returns to infinite Normal Normal Continuity Abnormal Normal Abnormal Continuity HIGH VOLTAGE CAPACITOR HIGH VOLTAGE DIODE NOTE Some inexpensive meter may indicate infinite resistance in both direction Measure the resistance Multi meter scale Rx1000 Terminal to case Measure the continuity Forward Multi meter sca...

Page 23: ... time Replace just the fuse if the switches operate normally Check for continuity of the switch with a Multi meter Normal Abnormal 0 c Approx 150 C Approx 150 C Normal Grill heater Approx 40 7 Ω at 20 30 C Normal more than 0 5M Ω FUSE Wire leads removed HEATER ELEMENT Wire leads removed OVEN THERMOSTAT Measure the resistance Multi meter scale Rx1 Measure the resistance with 500V 100M Ω insulation ...

Page 24: ... left figures Measure the resistance RELAY 1 4 OF P C B Disconnect the 7 pin connector from P C B See Schematic Dagram on page 11 RY1 Turn Table Fan Motor Oven Lamp RY4 Heater Moving Motor RELAY 4 5 OF P C B Wire leads removed RY3 Grill RY2 Microwave KEY PAD SENSOR Wire leads removed NOTE A MICROWAVE ENERGY LEAKAGE TEST MUST ALWAYS BE PERFORMED WHEN THE UNIT IS SERVICED FOR ANY REASON MAKE SURE TH...

Page 25: ...ck the primary the secondary and the monitor switches before replacing the fuse TROUBLE 1 Oven does not operate all CONDITION CAUSE OFF CONDITION The fuse blows when power cord is plugged into wall receptacle 0 does not appear in displasy window when power cord is first plugged into wall outlet Display does not operate properly when CLOCK is touched Shorted lead wise assy or wire hardness Defectiv...

Page 26: ...connection Incorrect touch key Defective secondary switch or out of adjustment Defective tact switch key of P C B Loose connection Loose PCB connector No CN6 and H M M S W1 S W2 Loose Gear of H M MOTOR Test procedure tact switch key of P C B Connect them tightly Touch key again after closing Test procedure secondary switch Test procedure tact switch key of P C B Test tact switch key of P C B To Fa...

Page 27: ...rntable motor does not operate Test procedure primary and secondary switches Test procedure relay 1 of P C B Test procedure tact switch key of P C B Check and repair wiring Test procedure fan motor Use the microwave oven at adequate line voltage This may not be a defect It is possible that the food should be cooked for a longer period Test procedure relay 2 of P C B Test procedure relay 2 of P C B...

Page 28: ...roti bar is using in no load condition Test procedure relay 2 of P C B Test procedure high voltage transformer and thermal Cut out of high voltage transformer Test procedure high voltage capacitor Test procedure high voltage diode Test procedure magnetron Use the microwave oven at adequate line voltage Check and repair wiring Do not use metallic ware for cooking except where noted in the cookbook ...

Page 29: ...r of moving heater motor and too loose of PCB connec tor CN6 Test procedure relay 3 of P C B Check and repair wiring Check and repair wiring Interchange live part wire with neutral part wire correctly Test procedure Moving heater Motor and PCB CN6 connector TEST PROCEDURE OR CORRECTION TROUBLE 3 Oven does not operating microwave cooking NOTE MAKE SURE THE WIRE LEADS CORRECT POSITION WHEN REMOVING ...

Page 30: ... resistance of Shield wire connector Remove the dirt from the filter Use Suitable utensil Refer to the owner s manual Refer to Schematic Diagram and adjust it Refer to page 24 Replace Sensor Ass y Check the connector Refer to page 24 Replace sensor Ass y TEST PROCEDURE OR CORRECTION TROUBLE 6 Uneven Cooking and Error during Sensor Cook and temperature process E 01 Sensor open or short E 02 Key sho...

Page 31: ...EXPLODED VIEW INTRODUCTION 31 DOOR PARTS CONTROL PANEL PARTS LATCH BOARD PARTS BASE PARTS INTERIOR PARTS OVEN CAVITY PARTS ...

Page 32: ...DOOR PARTS 32 13720D 13806D 13581A 14970A 14026A 13552A 13536A 15006A 13213A 14890A ...

Page 33: ...CONTROL PANEL PARTS 33 268711 WTP018 23572A 23790D 250202 250205 268712 249401 250201 24781S 250206 250204 250203 ...

Page 34: ...OVEN CAVITY PARTS 34 33052M 35301A 34960A 36549S WTP013 34810A 343501 34681R 344701 344702 466003 348102 34681R 568771 56501A 54826A 33112U WSZ002 33390G 32026G 34370T 35889A 36549H WSZ092 ...

Page 35: ...LATCH BOARD PARTS 35 43501A 466001 466003 466001 44510A 43500A WSZ085 ...

Page 36: ...INTERIOR PARTS 36 56411A 24970A 343502 34810H 33550H 34930W 35264A 948503 34930W 948501 56324A 35012A WSZ002 56912B 55262A 56851C 54810C 50CZZH 56549F 55900A 54974S 50FZZA 56201A WTT037 568773 568772 ...

Page 37: ...BASE PLATE PARTS 37 56170D 647781 WTT030 63303R 63303L 948502 ...

Page 38: ...MICOM CONTROLLER SCHEMATIC DIAGRAM 40 ...

Page 39: ...MICOM CONTROLLER P C B LAOUT 41 ...

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