LG MS-0746T Service Manual

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MICROWAVE OVEN

SERVICE MANUAL

MODEL: MS-0746T

CAUTION

BEFORE SERVICING THE UNIT, READ THE SAFETY PRECAUTIONS IN THIS MANUAL.

P/NO : MFL31039202

June, 2006

Printed in Korea

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 EXCESSIVE MICROWAVE ENERGY

A) Do not operate or allow the oven to be operated with the door open.

B) Make the following safety checks on all ovens to be serviced before activating the magnetron or other

microwave source, and make repairs as necessary; (1) interlock operation, (2) proper door closing, (3)

seal and sealing surfaces (arcing, wear, 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, and microwave generation

and transmission systems shall be repaired, replaced, or adjusted by procedures described in this manual

before the oven is released to the owner.

E) A microwave leakage check to verify compliance with the Federal Performance Standard should be

performed on each oven prior to release to the owner.

CAUTION

MICROWAVE RADIATION

DO NOT BECOME EXPOSED TO RADIATION FROM THE MICROWAVE GENERATOR OR OTHER PARTS CONDUCTING MICROWAVE ENERGY.

CONTENTS

(Page)

SAFETY PRECAUTIONS

SPECIFICATIONS

CAUTIONS

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INSTALLATIONS

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OPERATING INSTRUCTIONS

FEATURES

CONTROL PANEL

OPERATING SEQUENCE

SCHEMATIC DIAGRAM

CIRCUIT DESCRIPTION

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SERVICE INFORMATION

TOOLS AND MEASURING INSTRUMENTS

MICROWAVE LEAKAGE TEST

MEASUREMENT OF MICROWAVE POWER OUTPUT

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Inside front cover

1-1

2-1

3-1

4-1

4-2

4-3

4-4

5-1

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5-3

DISASSEMBLY AND ADJUSTMENT

INTERLOCK CONTINUITY TEST

COMPONENT TEST PROCEDURE

TROUBLE SHOOTING

EXPLODED VIEW

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REPLACEMENT PARTS LIST

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5-3

5-7

5-8

5-12

6-1

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7-1

SPECIFICATIONS

Control panel side

ITEM

MODEL

Power Requirement

Power Output

Microwave Frequency

Magnetron

Timer

Outside Dimensions

Cavity Dimensions

Net Weight

Shipping weight

Control Complement

DESCRIPTION

MS-0746T

120 Volts AC 60 Hz

950 Watts

Single phase, 3 wire grounded

700 Watts full microwave power (IEC60705)

2450 MHz

2M213 - 09B

10 sec. ~ 99 min. 50 sec

17 7/8” (W) x 10 9/16” (H) x 13” (D)

12 3/8” (W) x 7 15/16” (H) x 11 9/16” (D)

10.5 kg (approx.)

11.5 kg (approx.)

Microwave Power for Variable Cooking

Power level

HIGH .................................... Full power throughout the cooking time

9 (Saute)

7 (Med.-High)

5 (Med.-Low)

3 (Low)

1 (Warm)

...............................

........................

.................................

..............................

.......................

approx. 90% of Full power, 8 (Reheat)

approx. 70%, 6 (Medium)

approx. 50%, 4 (Defrost)

approx. 30%, 2 (Simmer)

approx. 10%

..........

approx. 80%

.........

approx. 60%

approx. 40%

.........

approx. 20%

Rating Label Location

Accessories

This microwave oven is designed for household use only.

It is not recommended for commercial purposes.

Owner's manual

Glass turntable

Roller Rest

1-1

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 during repair.

• DO NOT operate on a 2-wire extension cord during repair and use.

• NEVER TOUCH any oven components or wiring during operation.

• BEFORE TOUCHING any parts of the oven, always remove the power plug from the outlet.

• For about 30 seconds after the oven stops, an electric charge remains in the high voltage capacitor. When replacing or checking, you must discharge the high voltage capacitor by shorting across the two terminals with an insulated screwdriver.

MICROWAVE RADIATION

Personnel should not be exposed to the microwave energy which may radiate from the magnetron or other microwave generating device if it is improperly used or connection. All input and output microwave connections, waveguide, flange and gasket must be secure never operate the device without a microwave energy absorbing load attached. Never look into an open waveguide or antenna while the device is energized.

• Proper operation of the microwave oven requires that the magnetron 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.

ANTENNA

Gasket

•

Remove your watches whenever working close to or

replacing the Magnetron.

• NEVER operate the oven with no load.

• NEVER injure the door seal and front plate of the oven

cavity.

• NEVER put iron tools on the magnetron.

• NEVER put anything into the latch hole and the

interlock switches area.

COOLING FIN

FILAMENT TERMINALS

MAGNETRON CHASSIS GROUND

MAGNETRON

THE OVEN IS TO BE SERVICED ONLY BY PROPERLY QUALIFIED SERVICE PERSONNEL.

2-1

INSTALLATIONS

BEFORE YOU BEGIN, READ THE FOLLOWING INSTRUCTIONS COMPLETELY AND CAREFULLY.

INSTALLING

1. Empty the microwave oven and clean inside it with a soft, damp cloth. Check for damage such as misaligned door, damage around the door or dents inside the cavity or on the exterior.

2. Put the oven on a counter, table, or shelf that is strong enough to hold the oven and the food and utensils you put in it. (The control panel side of the oven is the heavy side. Use care when handling.)

3. Do not block the vent and the air intake openings. Blocking vent or air intake openings can cause damage to the oven and poor cooking results. Make sure the microwave oven legs are in place to ensure proper air flow.

4. The oven should not be installed in any area where heat and steam are generated, because they may damage the electronic or mechanical parts of the unit. Do not install the oven next to a conventional surface unit or above a conventional wall oven.

5. Use microwave oven in an ambient temperature less than 104°F(40°C).

EARTHING INSTRUCTIONS

This microwave oven is designed to be used in a fully earthed condition. It is imperative, therefore, to make sure it is properly earthed before servicing

WARNINGTHIS APPLIANCE MUST BE EARTHED

IMPORTANT

The wires in this mains lead are colored in accordance with the following code:

Green-and-yellow: Earth Blue: Neutral Brown: Live

As the colors of the wires in the mains lead of this appliance may not correspond with the colored markings identifying the terminals in your plug, proceed as follows.

6. Place the microwave oven on a sturdy and flat surface at least 10 cm(4 inches) from the wall.

7. Place the microwave oven as far away as possible from TV, RADIO, COMPUTER, etc., 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.

10cm

The wire which is colored green-and-yellow must be connected to the terminal in the plug which is marked with the letter E or by the earth symbol ( ) or colored green or green-and-yellow.

The wire which is colored blue must be connected to the terminal in the plug which is marked with the letter N or colored black.

The wire which is colored brown must be connected to the terminal in the plug which is marked with the letter L or colored red.

3-1

OPERATING INSTRUCTIONS

Oven Front Plate

Window Door Screen

Door Seal

Safety Door Lock System Turntable

Roller rest

Control Panel

FEATURES

CONTROL PANEL

1. INDICATORS

2. ONE TOUCH CONTROL: Used to cook the foods

listed by one touch.

3. AUTO DEFROST: Used to select the auto weight defrost.

4. QUICK DEFROST: Used to select the auto weight defrost.

5. NUMBER: Used to set for time of day, cooking time, power level or defrost weight.

6. TIME: Used to cook food for a desired time.

7. POWER: Used to select power level for cooking.

8. STOP/CLEAR: Used to stop over and clear all

entries except time of day.

9. START: One tap allows over to begin functioning.

10. CLOCK: Used to set the time of day.

9 10

4-1

OPERATING SEQUENCE

The following is a description of component functions during oven operation.

1. SETTING THE CLOCK

PARAR/

BORRAR

NOTE: 1) This is a 24 hour clock.

2) Clock will operate as long as power is applied to the oven.

RELOJ RELOJ

NUMBER

2. CANCEL FUNCTION

Touch the pad whenever you need to cancel an entry or a function currently in use. The display will either return to the last item entered or to the clock.

PARAR/BORRAR

3. ONE TOUCH COOKING

PARAR/

BORRAR

NOTE: Heat only 1 package at a time

PALOMITAS

DE MAIZ

5.MULTI-STAGE COOKING

1ST STAGE

PARAR/

BORRAR

2ND STAGE

1ST STAGE

TIEMPO

NUMBER

TIEMPO

NUMBER

INICIO

6.AUTO DEFROST COOKING

PARAR/

BORRAR

DESCONGELADO

AUTOMATICO

NUMBER OF

WEIGHT

POTENCIA

INICIO

4.TIME COOKING

PARAR/

BORRAR

TIEMPO

NUMBER

INICIO

7. CHILD LOCK

POTENCIANUMBER

This oven has a CHILD LOCK feature

TO SET CHILD LOCK

• Touch the pad

• Touch and hold 0 pad L appear on

the display.

TO CANCEL CHILD LOCK

• Touch the pad

• Touch and hold 0 pad L disappear.

4-2

SCHEMATIC DIAGRAM

4-3

CIRCUIT DESCRIPTION

FUSE

H.V.

TRANS-

FORMER

RELAY 2

MICOM CONTROLLER

SECONDARY SWITCH

PRIMARY

SWITCH

MONITOR

SWITCH

GENERAL DETAILS

• The low voltage transformer supplies the necessary voltage to the micom controller when power cord is plugged in.

• When the door is closed, the primary switch is ON, the

secondary switch is ON, and the monitor switch opens (contact COM and NO).

WHEN SELECTING COOKING POWER LEVEL AND TIME

• The micom controller memorizes the function you set.

• The time you set appears in the display window.

• Each indicator light turns on to indicate that the stage

has been set.

WHEN TOUCHING THE START PAD

• The coil of the relay is energized by the micom

controller.

• Power input is supplied to the high voltage transformer

through the fuse to the primary switch and relay 2.

• Turntable rotates.

power of microwave oven as POWER LEVEL.

(refer to page 1-1)

WHEN THE DOOR IS OPENED DURING COOKING

• Both the primary switch and relay 2 are cut off primary winding voltage of the high voltage transformer.

• ON-OFF of relay 2 is coupled electrically with opening and closing of the secondary switch.

• When the door is opened, the secondary switch is opened and when the door is closed, the secondary switch is closed.

• The cooking time stops counting down.

• Relay stops functioning.

• As the door is opened, if the contact of primary switch

and relay 2 and/or secondary switch fails to open, the fuse opens due to the large current surge caused by the monitor switch activation, which in turn stops magnetron oscillation.

PRIMARY

FUSE

SWITCH

MONITOR

SWITCH

H.V.

TRANS-

FORMER

• The fan motor rotates and cools the magnetron by blowing the air (coming from the intake on the baseplate).

• The air is also directed into the oven to exhaust the vapor in the oven through the upper plate.

• Cooking time starts counting down.

• 3.2 volts AC is generated from the filament winding of

the high voltage transformer. This 3.2 volts is applied to the magnetron to heat the magnetron filament through two noise-preventing choke coils.

• A high voltage of approximately 2100 volts AC is generated in the secondary of the high voltage transformer which is increased by the action of the high voltage diode and charging of the high voltage capacitor.

• The negative 4000 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

MICOM CONTROLLER

RELAY 2

SECONDARY SWITCH

4-4

SERVICE INFORMATION

TOOLS AND MEASURING INSTRUMENTS

NECESSARY TOOLS

Tools normally used for TV servicing are sufficient. Standard tools are listed below.

• Diagonal pliers

• Long nose pliers

• Phillips screwdriver

• Flat blade screwdriver

• Wrench (size 5mm)

• Nutdriver (size 5mm)

• Adjustable wrench

• Soldering iron

• Solder

• Vinyl insulation tape

• Polishing cloth

MICROWAVE LEAKAGE TEST

CAUTIONS

• Be sure to check microwave leakage prior to servicing the oven if the oven is operative prior to servicing.

• The service personnel should inform the manufacture importer, or assembler of any certified oven unit found to have a microwave emission level in excess of 5 mW/cm2and should

repair any unit found to have excessive emission levels at no cost to the owner and should ascertain the cause of the excessive leakage. The service personnel should instruct the owner not to use the unit until the oven has been brought into compliance.

• If the oven operates with the door open, the service personnel should:

- Tell the user not to operate the oven.

- Contact the manufacturer.

• The service personnel should check all surface and vent openings for microwave leakage.

• Check for microwave leakage after every servicing. The power density of the microwave radiation leakage emitted by the microwave oven should not exceed 4 mW/cm2. Always start measuring of an unknown field to assure safety for operating personnel from radiation leakage.

NECESSARY MEASURING INSTRUMENTS

• TESTER(VOLTS-DC, AC., Ohmmeter)

• Microwave survey meter

- Holaday HI-1500 HI-1501

- Narda 8100

8200

• Inch scale

• 600 cc non conductive material beaker (glass or plastic),

inside diameter: approx. 8.5 cm(3

• Cylindrical and made of borosilicate glass vessel. max. thickness: 3 mm outside diameter: approx. 190mm height: approx. 90mm

• Glass thermometer: 100°C or 212°F (1 deg scale)

/2 in.)

MEASURING MICROWAVE ENERGY LEAKAGE

• Pour 275±15cc of 20±5°C(68±9°F) water in a beaker

which is graduated to 600 cc, and place the beaker on the center of the turntable.

• Set the energy leakage monitor to 2450 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 radiation monitor by holding the probe perpendicular to the surface being measured

Move probe along shaded area

Probe scanning speed Less than 2.5 cm/sec ( 1in/sec)

5-1

MEASUREMENT WITH OUTER CASE REMOVED

• When you replace the magnetron, measure for microwave energy leakage before the outer case is installed and after all necessary components are replaced or adjusted.

Special care should be taken in measuring the

following parts. (Circled area of below Fig.)

- Around the magnetron

- The waveguide

WARNING : AVOID CONTACTING ANY

HIGH VOLTAGE PARTS

NOTES WHEN MEASURING

• Do not exceed meter full scale deflection.

• The 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 the oven surface, this may possibly cause probe damage.

RECORD KEEPING AND NOTIFICATION AFTER MEASUREMENT

• After adjustment and repair of any microwave energy interruption or microwave energy blocking device, record the measured values for future reference. Also enter the information on the service invoice.

• The microwave energy leakage should not be more than 4 mW/cm.sq. after determining that all parts are in good condition, functioning properly and genuine replacement parts which are listed in this manual have been used.

• At least once a year, have the electromagnetic energy leakage monitor checked for calibration by its manufacturer.

MEASUREMENT WITH A FULLY ASSEMBLED OVEN

• After all components, including the outer case, are fully assembled, measure for microwave energy leakage around the door viewing window, the exhaust opening, and air inlet openings.

• Microwave energy leakage must not exceed the values prescribed below.

NOTE: Leakage with the outer case removedless than

5 mW/cm.sq. Leakage for a fully assembled oven (Before the latch switch (primary) is interrupted) with the door in a slightly opened position-less than 2 mW/cm.sq.

5-2

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