LG 3828W5S2388 Service Manual

P/NO : 3828W5S2388

Website: http://biz.lgservice.com

July ., 2002

Printed in Korea

MICROW AVE OVEN

SER VICE MANUAL

MODEL: MD-0942GT

CAUTION

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

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.

SAFETY PRECAUTIONS

CAUTION

MICROWAVE RADIATION

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

(Page)

SAFETY PRECAUTIONS

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Inside front cover

SPECIFICATIONS

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1-1

CAUTIONS

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2-1

INSTALLATIONS

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3-1

OPERATING INSTRUCTIONS

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4-1

FEATURES

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4-1

CONTROL PANEL

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4-1

OPERATING SEQUENCE

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4-2

SCHEMATIC DIAGRAM

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4-3

CIRCUIT DESCRIPTION

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4-4

SERVICE INFORMATION

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5-1

TOOLS AND MEASURING INSTRUMENTS

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5-1

MICROWAVE LEAKAGE TEST

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5-1

MEASUREMENT OF MICROWAVE POWER OUTPUT

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5-3

DISASSEMBLY AND ADJUSTMENT

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5-3

INTERLOCK CONTINUITY TEST

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5-7

COMPONENT TEST PROCEDURE

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5-8

TROUBLE SHOOTING

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5-12

EXPLODED VIEW

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6-1

REPLACEMENT PARTS LIST

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7-1

SCHEMATIC DIAGRAM OF P.C.B.

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8-1

PRINTED CIRCUIT BOARD

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8-2

P.C.B. PARTS LIST

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9-1

CONTENTS

This microwave oven is designed for household use only. It is not recommended for commercial purposes.

DESCRIPTION

MD-0942GT

120 Volts AC 60 Hz Single phase, 3 wire grounded Microwave 1,250W Toast 550W 900 Watts full microwave power (IEC60705) 2,450 MHz 2M214 - 39F 0 ~ 90 min. 512 (W) x 302 (H) x 395 (D) mm 320 (W) x 233 (H) x 347 (D) mm

16.5 kg (approx.) 18 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

TOAST, COMBI

Owner's manual Glass turntable Rotating ring

1-1

ITEM

MODEL

Power Requirement

Power Output Microwave Frequency Magnetron Timer Outside Dimensions Cavity Dimensions Net Weight Shipping weight Control Complement

Nameplate Location

Accessories

SPECIFICATIONS

Back side

• 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.

•

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.

• 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.

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 during repair.

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

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.

Gasket

ANTENNA

COOLING FIN

MAGNETRON CHASSIS GROUND

FILAMENT TERMINALS

MAGNETRON

INSTALLATIONS

3-1

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).

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.

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

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.

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.

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

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

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

10cm

4-1

OPERATING INSTRUCTIONS

FEATURES

CONTROL PANEL

Rotating Ring

Control Panel

Safety Door Lock System

Turntable

Oven Front Plate

Window Door Screen

Door Seal

Toast

736 1

42 8

1. COOK TIME: Used to cook food for a desired time.

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

3. POWER: Used to select the desired power level for cooking.

4. AUTO COOK: Used to cook the foods listed by one touch.

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

6. STOP/CLEAR: Used to stop over and clear all entries except time of day.

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

8. TOAST START/STOP: Start or stop for toast.

9. TOAST COOK TIME: Used to set the toast.

4-2

OPERATING SEQUENCE

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

1. SETTING THE CLOCK

NOTE: You can set 12 hour clock or 24 hour clock

optionally.

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.

3. QUICK START

4. MICROWAVE COOKING

5. TOAST

6. TWO STAGE COOKING

7. AUTO WEIGHT DEFROST

8. AUTO COOK

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.

Parar/ Borrar

Reloj Set the hour

Set the

minute

Inicio

Parar/Borrar Inicio

Parar/Borrar

Inicio

Parar/ Borrar

Desired

defrost

category

Desired cooking

weight

Inicio

Parar/ Borrar

Potencia Time

Parar/ Borrar

Time Inicio

Parar/ Borrar

Potencia Time

Potencia Time Inicio

Inicio

Parar/Borrar

SCHEMATIC DIAGRAM

4-3

Fuse

CIRCUIT DESCRIPTION

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 3.

• Turntable rotates.

• 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 4,000 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 3 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 3 is 22 seconds.

WHEN THE DOOR IS OPENED DURING COOKING

• Both the primary switch and relay 3 are cut off primary winding voltage of the high voltage transformer.

• ON-OFF of relay 3 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 fails to open, the fuse opens due to the large current surge caused by the monitor switch activation, which in turn stops magnetron oscillation.

WHEN TOUCHING THE START KEY WITH THE GRILL COOKING FUNCTION SELECTED

• The contacts of the primary switch and the secondary

switch close the circuit.

• A.C. voltage is applied to the toast heater through toast thermostat as shown by the solid line.

• Turntable rotates.

• The fan motor rotates.

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

4-4

FUSE

H.V.

TRANS-

FORMER

RELAY 3

MICOM CONTROLLER

SECONDARY SWITCH

PRIMARY

SWITCH

MONITOR

SWITCH

FUSE

PRIMARY

SWITCH

MONITOR

SWITCH

H.V.

TRANS-

FORMER

RELAY 3

MICOM CONTROLLER

SECONDARY SWITCH

G -Y

RELAY 4

TOAST

HEATER

TOAST

THERMOSTAT

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/cm

. Always start measuring of an unknown field to assure safety for operating personnel from radiation leakage.

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 2,450 MHz and use it following the manufacturer's recommended test procedure to assure correct result.

• When measuring the leakage, always use the 2inch (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

SERVICE INFORMATION

TOOLS AND MEASURING INSTRUMENTS

MICROWAVE LEAKAGE TEST

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

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

/2 in.)

• 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)

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

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.

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.

WARNING : AVOID CONTACTING ANY

HIGH VOLTAGE PARTS

5-2

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