LG MH-794GS Service Manual
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LG MH-794GS Service Manual

LG MH-794GS Service Manual

Microwave/grill oven
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MICROWAVE/
GRILL OVEN
SERVICE MANUAL
MODEL : MH-794GS
CAUTION
BEFORE SERVICING THE UNIT, READ THE SAFETY PRECAUTIONS
IN THIS MANUAL.

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Summary of Contents for LG MH-794GS

  • Page 1 MICROWAVE/ GRILL OVEN SERVICE MANUAL MODEL : MH-794GS CAUTION BEFORE SERVICING THE UNIT, READ THE SAFETY PRECAUTIONS IN THIS MANUAL.

  • Page 2: Safety Precautions

    SAFETY PRECAUTIONS This device is to be serviced only by properly qualified service personnel. Consult the Service Manual for proper service procedures to assure continued safety operation and for precautions to be taken to avoid possible exposure to excessive microwave energy. PRECAUTIONS TO BE OBSERVED BEFORE AND DURING SERVICING TO AVOID POSSIBLE EXPOSURE TO...

  • Page 3: Table Of Contents

    TABLE OF CONTENTS (Page) SAFETY PRECAUTIONS Inside front cover SPECIFICATIONS CAUTIONS INSTALLATIONS OPERATING INSTRUCTIONS FEATURES CONTROL PANEL AUTO MOVING HEATER GUIDE OPERATING SEQUENCE SCHEMATIC DIAGRAM CIRCUIT DESCRIPTION SERVICE INFORMATION TOOLS AND MEASURING INSTRUMENTS MICROWAVE LEAKAGE TEST MEASUREMENT OF MICROWAVE POWER OUTPUT DISASSEMBLY AND ADJUSTMENT INTERLOCK CONTINUITY TEST COMPONENT TEST PROCEDURE...

  • Page 4: Specifications

    SPECIFICATIONS ITEM DESCRIPTION MODEL MH-794GS Power Requirement 230V AC 50Hz Single phase, 3 wire grounded Microwave 1200W Grill 1150W Combination 2300W Power Output 900W full microwave power(IEC705) Microwave Frequency 2,450MHz Magnetron 2M214 - 39F Timer 99min. 90sec. Outside Dimensions 556mm(W) X 322mm(H) X 435mm(D)

  • Page 5: Cautions

    CAUTIONS Unlike other appliances, the microwave oven is MICROWAVE RADIATION high-voltage and high-current appliance. Personnel should not be exposed to the Though it is free from danger in ordinary use, microwave energy which may radiate from the extreme care should be taken during repair. magnetron or other microwave generating device if it is improperly used or connected.

  • Page 6: Installations

    INSTALLATIONS BEFORE YOU BEGIN, READ THE FOLLOWING INSTRUCTIONS COMPLETELY AND CAREFULLY. Installing microwave oven Earthing Instructions 1. Empty the microwave oven and clean inside it with This microwave oven is designed to be used in a fully a soft, damp cloth. Check for damage such as earthed condition.

  • Page 7: Operating Instructions

    OPERATING INSTRUCTIONS Features Oven front face Window Door Screen Door Seal Display Window Control Panel Shaft Latch Grill Rack Glass Tray Rotating ring ASS'Y Control Panel DISPLAY INDICATOR- Shows: COOKING MODE Time of Day, ¥ Set the cooking mode Cooking power Level, (Microwave, Grill, Combination) Cooking Category.

  • Page 8: Auto Moving Heater Guide

    Auto Moving Heater Guide GRILL HEATER POSITION COOK • Cooking • Cooking Stop • Next Cook Setting CATEGORY • Door Open • Door Closed ater cook • Cooking End is ended and food is removed Microwave Cook 1. Jacket Potato Sensor 2.

  • Page 9: Operating Sequence

    Operating Sequence The following is a description of component functions during oven operation. Plug the power cord into an Clock electric outlet Set the Set the 2times correct hour correct minute M/W Cook Stop/ Desired Set the correct minute Clear power level Grill Cook Stop/...
  • Page 10 Operating Sequence The following is a description of component functions during oven operation. To Set CHILD LOCK • "L" appears on the display and you can't input any key. Stop/ Stop/Clear Clear Touch and Hold Child Lock To Cancel CHILD LOCK •...

  • Page 11: Schematic Diagram

    SCHEMATIC DIAGRAM...

  • Page 12: Circuit Description

    Circuit Description GENERAL DETAILS output power of microwave oven as POWER LEVEL. (refer to page 1-1) • The low voltage transformer supplies the necessary • One complete cycle of relay 5 is 22 seconds. voltage to the micom controller when power cord is WHEN THE DOOR IS OPENED plugged in.

  • Page 13: Service Information

    SERVICE INFORMATION Tools and Measuring Instruments NECESSARY MEASURING NECESSARY TOOLS INSTRUMENTS Tools normally used for TV servicing are sufficient. • TESTER (VOLTS-DC, AC, Multmeter) • Microwave survey meter Standard tools are listed below. —Holaday H1-1500, Hi-1501 • Diagonal pliers —Narda 8100, 8200 •...
  • Page 14 MEASUREMENT WITH THE OUTER NOTES WHEN MEASURING CASE REMOVED Do not exceed meter full scale deflection. The test probe must be removed no faster than, When you replace the magnetron, measure microwave 1 inch/sec (2.5 cm/sec) along the shaded area, energy leakage before the out case is installed and otherwise a false reading may result.

  • Page 15: Measurement Of Microwave Power Output

    Measurement of Microwave Power Output Microwave power output measurement is made with The microwave power output P in watts is calculated the microwave oven supplied at its rated voltage and from the following formula: operated at its maximum microwave power setting with 4187 X ∆T a load of (1000 ±...
  • Page 16 D. DOOR GROSS ASSEMBLY REMOVAL E. HIGH VOLTAGE TRANSFORMER REMOVAL 1) Open the door. 2) Remove the choke cover cap very carefully with a 1) Discharge the high voltage capacitor. flat-blade screwdriver. 2) Disconnect the leadwire from magnetron, high CAUTION : Be careful not to damage door seal plate voltage transformer, and capacitor.
  • Page 17 H. AIR DUCT ASSEMBLY REMOVAL J. REMOVING THE TURNTABLE MOTOR 1) Disconnect the leadwire from lamp and MGT ther mostat. 1) Remove the turntable. 2) Remove the mounting screw to the cavity. 2) Remove the turntable shaft VERY CAREFULLY with a slotted hand.
  • Page 18 K. Auto Moving Heater MOTORE ASS'Y L. Sensor ASS'Y Heater Gasket Bracket Ass’y Cover Joint-Spring Terminal 1. Remove the Screw of the back and on the Cavity. 2. Remove the Screw of the Bracket. 3. Remove the Bracket. 1. Remove the Screw of the Back and in the Cavity. 4.
  • Page 19 M. PCB ASSEMBLY REMOVAL 1) Remove the control panel assembly from the 2) MOUNTING OF THE PRIMARY/MONITOR/ cavity.(Refer to control panel assembly removal on SECONDARY SWITCHS TO THE LATCH BOARD previous page.) 2) Remove screws which hold the PCB SUB ASS'Y to ADJUSTMENT the control panel.

  • Page 20: Interlock Continuity Test

    Interlock continuity Test WARNING : FOR CONTINUED PROTECTION AGAINST EXCESSIVE RADIATION EMISSION, REPLACE ONLY WITH IDENTICAL REPLACEMENT PARTS. TYPE NO. SZM-V 16-FA-63 OR VP-533A-OF FOR PRIMARY SWITCH TYPE NO. SZM-V 16-FA-62 OR VP-532A-OF FOR MONITOR SWITCH TYPE NO. SZM-V 16-FA-63 OR VP-533A-OF FOR SECONDARY SWITCH A.

  • Page 21: Component Test Procedure

    Component Test Procedure CAUTIONS 1. DISCONNECT THE POWER SUPPLY CORD FROM THE OUTLET WHENEVER REMOVING THE OUT 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.
  • Page 22 COMPONENTS TEST PROCEDURE RESULTS Antenna Gasket Chassis Filament Terminals 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. Measure the resistance. Normal : Momentary HIGH VOLTAGE (Multi-meter scale : Rx1000) indicates several...
  • Page 23 COMPONENTS TEST PROCEDURE RESULTS Normal Abnormal Check for continuity of the switch with a FUSE Multi-meter. (Wire leads removed.) NOTE : If the fuse is blown, check the primary, the secondary, and the monitor switches, H.V.D. and H.V.C. before replacing the fuse. If the fuse is blown by improper switch operation replace the defective switch and the fuse at the same time.
  • Page 24 COMPONENTS TEST PROCEDURE RESULTS RELAY 1,4, OF P.C.B Cooking Start (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 1 Relay 4 RELAY 4, 5 OF P.C.B Cooking Start (Wire leads removed.)

  • Page 25: Trouble Shooting Guide

    Trouble Shooting Guide CAUTIONS 1. Check grounding before checking for other trouble. 2. Be careful of the high voltage circuit. 3. When checking the continuity of the switches or transformer, disconnect one lead wire from these parts and then check continuity without turning the power source on. 4.
  • Page 26 (TROUBLE 2) Oven does not at all even thought MOTOR and P.C.B program. TEST PROCEDURE OR CONDITION CAUSE CORRECTION No input can be Defective tact switch key of Test procedure tact switch programmed. P.C.B. key of P.C.B. Some inputs can not be Loose connection.
  • Page 27 (TROUBLE 3) Oven does not operating microwave cooking TEST PROCEDURE OR CONDITION CAUSE CORRECTION Oven does not go into a Primary and secondary Test procedure primary and cook cycle when START key interlock switches defective secondary switches. is touched. or out of adjustment. Test procedure relay 1 of Defective relay 1 of P.C.B.
  • Page 28 (TROUBLE 3) Oven does not operating microwave cooking TEST PROCEDURE OR CONDITION CAUSE CORRECTION Test procedure relay 2 of No microwave oscillation. Defective relay 2 of P.C.B. P.C.B. • Defective high voltage Test procedure high voltage transformer. transformer and thermal •...
  • Page 29 (TROUBLE 3) Oven does not operating microwave cooking TEST PROCEDURE OR CONDITION CAUSE CORRECTION Grill indicator lights Test procedure relay 3 of Defective relay 3 of P.C.B. P.C.B. but oven does not go into cook cycle when START key is touched. Open or loose wire Check and repair wiring.
  • Page 30 (TROUBLE 6) Uneven Cooking and Error during Sensor Cook and temperature process. TEST PROCEDURE OR CONDITION CAUSE CORRECTION Remove the dirt from the Poor Cooking Dirt on the Sensor Filter filter. Unsuitable utensil was Use Suitable utensil. used. Refer to the owner’s manual. Incorrect connection of Refer to Schematic Diagram Shield wire.

  • Page 31: Exploded View

    EXPLODED VIEW INTRODUCTION OVEN CAVITY PARTS INTERIOR PARTS DOOR PARTS BASE PARTS LATCH BOARD PARTS CONTROL PANEL PARTS...
  • Page 32 DOOR PARTS 13581A 15006A 13536A 13552A 13213A 14890A 14026A 14970A 13720D 13806D...
  • Page 33 CONTROL PANEL PARTS 24781S 268711 268712 WTP018 23790D 250201 250205 23572A 250202 249401 250206 250204 250203...
  • Page 34 OVEN CAVITY PARTS 33112U 54826A 33052M WSZ002 WSZ092 56501A 32026G 34810A 344702 33390G 466003 343501 35301A 34370T 348102 36549H 34681R 344701 35889A 568771 34960A 36549S WTP013 34681R...
  • Page 35 LATCH BOARD PARTS 43501A 466001 466003 WSZ085 44510A 43500A 466001...
  • Page 36 INTERIOR PARTS 34810H 33550H 56411A 34930W 24970A 343502 35264A 948503 50FZZA 56201A 34930W WTT037 54974S 35012A 55900A 56549F 56324A WSZ002 50CZZH 948501 56912B 54810C 56851C 568772 568773 55262A...
  • Page 37 BASE PLATE PARTS 56170D 948502 63303L 63303R 647781 WTT030...

  • Page 38: Replacement Parts List

    MICOM CONTROLLER SCHEMATIC DIAGRAM...

  • Page 39: Micom Controller P.c.b Layout

    MICOM CONTROLLER P.C.B. LAOUT...

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