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LG MH-1355M - User Manual

LG MH-1355M
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MICROWAVE OVEN
SERVICE MANUAL
MODEL: MH-1355M
MH-1356M
MH-1357M
CAUTION
BEFORE SERVICING THE UNIT, READ THE SAFETY PRECAUTIONS IN THIS MANUAL.
Website: http://biz.lgservice.com
P/NO : 3828W5S6174
July, 1998
Printed in Korea

Table of Contents

Questions and Answers

  • L
    Laura BallardJul 31, 2025
    Why is my LG MH-1355M Microwave Oven sparking?
    • B
      Benjamin EvansJul 31, 2025
      Sparks can occur in your LG Microwave Oven for several reasons: * Using metallic ware that touches the oven wall. Avoid metallic ware, unless specifically allowed in the cookbook. * Using ceramic ware with gold or silver powder trimming. Do not use cookware with metallic trimming. * Food does not turn during cooking. If food or cookware extends beyond the turntable edges, rearrange it to allow turning.
  • J
    Jerry CoxAug 5, 2025
    Why is the temperature in my LG Microwave Oven lower or higher than preset?
    • P
      Paul RobinsonAug 5, 2025
      If the temperature in your LG Microwave Oven is not as expected, it could be due to: * A defective relay 4 or 2 of the P.C.B. * A defective convection heater element. * A defective thermistor. * A defective circulation motor. * A defective drive mechanism of the circulation fan. Check and repair the drive mechanism. * A defective Solenoid. * A defective air duct assembly. Check and repair the air duct assembly.
  • J
    joshua94Aug 9, 2025
    Why won't the oven light turn on when I open the door of my LG MH-1355M Microwave Oven?
    • B
      bensongabriellaAug 9, 2025
      If the light in your LG Microwave Oven doesn't turn on when you open the door: * There might be no power in your home. Check the wall outlet. * There could be an open wire in the power cord or wire harness. Replace or repair the wiring. * The oven lamp switch may be defective or out of adjustment. * The oven light itself might be defective and need replacement. * There might be an open or loose wire connection to the components. Check the wiring. * The fuse or oven light may be blown.
  • E
    elizabethvegaAug 14, 2025
    Why doesn't the oven light turn on during the cook cycle in my LG MH-1355M Microwave Oven?
    • D
      Desiree CookAug 14, 2025
      If the oven light doesn't turn on during the cook cycle in your LG Microwave Oven, it could be due to: * A defective relay 3 of the P.C.B.
  • J
    jluceroAug 20, 2025
    Why does the turntable motor operate normally but circulation motor does not operate in my LG MH-1355M?
    • F
      fosterstephanieAug 20, 2025
      If the turntable motor works but the circulation motor doesn't in your LG Microwave Oven: * Relay 4 of the P.C.B. may be defective. * The circulation motor itself could be defective. * There might be open or loose wiring to the circulation motor. Check and repair the wiring.
  • R
    Ryan AndersonAug 25, 2025
    What to do if ":0" does not appear in display window when power cord is first plugged into wall outlet of my LG MH-1355M Microwave Oven?
    • T
      Theresa MillerAug 25, 2025
      If ":0" does not appear in the display when you first plug in your LG Microwave Oven: * Ensure the microwave oven plug is fully and securely inserted into the wall outlet.

Summary

Safety Precautions for Microwave Oven Service

Microwave Oven Specifications

General Cautions and Microwave Radiation

Microwave Radiation Precautions

Precautions regarding exposure to microwave energy during operation or use.

Microwave Oven Installation Guidelines

Earthing Instructions for Safety

Proper grounding procedures for the microwave oven to ensure safety and compliance.

Microwave Oven Feature Diagram

Control Panel Overview and Functions

How the Microwave;Convection Oven Works

Microwave Cooking Explanation

Explanation of how food is cooked using only microwave energy.

Convection Cooking Explanation

Explanation of cooking with hot air circulated by a fan.

Combination Cooking Explanation

Explanation of cooking using both microwave energy and hot air.

Operating Instructions for Microwave Oven

Setting the Time of Day

Step-by-step guide for setting the current time on the oven display.

Using the Regular Timer

Instructions for using the oven as a simple timer without cooking functions.

Micro Time Cooking Procedure

Guide for setting microwave cooking time and power levels.

Convection Cooking Procedure

Instructions for preheating and cooking using convection mode.

Microwave Oven Schematic Diagrams

System 1: Stand-by Condition Schematic

Diagram illustrating the oven's electrical state when idle and powered.

Circuit Description for Oven Operation

Magnetron Tube Function and Testing

Testing the Magnetron Tube

Procedure for testing the magnetron using an ohmmeter for continuity and resistance.

Description and Function of Oven Components

Major Mechanical Components

Description of key mechanical parts like motors, door mechanisms, and heating elements.

Safety and Control Components

Explanation of safety switches, thermostats, and control elements.

Lighting Components

Description of the oven lamp and its switch.

Convection Cooking System and Chamber Assembly

Chamber Assembly Details

Describes the oven cavity's airflow path for convection cooking.

Damper Operation Control

Explains how the damper controls airflow for different cooking modes.

Necessary Tools and Measuring Instruments

Installation and Adjustment of Interlock System

Interlock System Installation Procedure

Steps for installing interlock switches.

Interlock System Adjustment Procedure

Steps for adjusting interlock switches to prevent microwave leakage.

Interlock Continuity Test Procedures

Primary Interlock Switch Continuity Test

Procedure for testing the continuity of the primary interlock switch.

Secondary Interlock Switch Continuity Test

Procedure for testing the continuity of the secondary interlock switch.

Monitor Switch Continuity Test

Procedure for testing the continuity of the monitor switch.

Disassembly and Parts Replacement Procedures

Removing Outer Case

Steps to remove the external casing of the microwave oven.

Removing Control Panel and PCB Assembly

Procedure for removing the control panel and printed circuit board.

Removing Door Assembly

Steps for disassembling and removing the oven door.

Component Removal Procedures (Magnetron, Fan, HV)

Removing Magnetron

Procedure for removing the magnetron component.

Removing Cooling Fan Motor

Steps to remove the cooling fan motor.

Removing High Voltage Diode and Capacitor

Procedure for removing the high voltage diode and capacitor.

Component Removal Procedures (Transformer, Turntable Motor)

Removing High Voltage Transformer

Steps to remove the high voltage transformer.

Removing Turntable Motor

Procedure for removing the turntable motor.

Component Removal Procedures (Circulation Motor, Heater, Switches)

Removing Circulation Motor

Steps to remove the circulation motor.

Removing Convection Heater and Thermistor

Procedure for removing the convection heater and thermistor.

Removing Primary Interlock Switch

Steps for removing the primary interlock switch.

Removing Secondary, Monitor, and Lamp Switches

Procedure for removing secondary interlock, monitor, and lamp switches.

Troubleshooting Oven Off Conditions

Troubleshooting Off Conditions

Troubleshooting steps for issues occurring when the oven is not in a cooking cycle.

Troubleshooting Oven Cooking Conditions

Troubleshooting Cooking Conditions

Troubleshooting for problems during the cooking cycle, like light or motor issues.

Troubleshooting Input and Display Issues

Troubleshooting Input;Display Issues

Troubleshooting for problems related to programming inputs or display readings.

Troubleshooting Microwave Operation Issues

Microwave Power, Sparking, and Uneven Cooking

Troubleshooting for microwave operation faults like low power or uneven cooking.

Troubleshooting Microwave Oscillation and Power

Microwave Oscillation and Power Level Issues

Troubleshooting for no microwave oscillation or incorrect power output.

Troubleshooting Convection Operation Issues

Convection Indicator, Temperature, and Airflow Issues

Troubleshooting for convection mode faults like indicator lights, temperature, or airflow problems.

Component Test Procedures: HV Transformer and Magnetron

Testing High Voltage Transformer and Magnetron

Procedures for testing the high voltage transformer and magnetron resistance.

Component Test Procedures: HV Capacitor and Diode

Testing High Voltage Capacitor and Diode

Procedures for testing the high voltage capacitor and diode continuity.

Component Test Procedures: Switches, Motors, and Fan

Testing Oven Lamp Switch, Motors, and Fan

Procedures for testing oven lamp switch, fan, turntable, and circulation motors.

Component Test Procedures: Fuse, Heater, and Solenoid

Testing Fuse, Heater Element, and Solenoid

Procedures for testing the fuse, heater element, and solenoid.

Component Test Procedures: PCB Relays

Testing PCB Relays 3 and 4

Procedures for testing the continuity of PCB relays 3 and 4.

Component Test Procedures: Membrane Keypad

Testing Membrane Keypad Switches

Procedure for checking the continuity of membrane keypad switches.

Procedure for Measuring Microwave Energy Leakage

Microwave Energy Leakage Measurement

Steps and equipment for measuring microwave radiation leakage.

Leakage Measurement with Outer Case Removed

Specific points to check for leakage when the outer case is off.

Microwave Power Output Measurement Procedures

Leakage Measurement with Fully Assembled Oven

Leakage measurement procedures for the assembled oven.

Determination of Microwave Power Output

Method and formula for calculating microwave power output.

Exploded View and Parts List Introduction

Door Parts Identification

Control Panel Parts Identification

Oven Cavity Parts Identification

Oven Interior Parts Identification (1)

Oven Interior Parts Identification (2)

Switches Parts Identification

Base Plate Parts Identification

Wiring Harness Parts Identification

Circuit Board Layout

Circuit Board Schematic Diagram

LG MH-1355M Specifications

General IconGeneral
TypeMicrowave Oven
Power Output900 W
Control TypeElectronic
TurntableYes
Cooking Levels5

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