LG 3828W5S1803 Service Manual

MICROW AVE OVEN

SER VICE MANUAL

MODEL : MB-314XF

MB-314XB

CAUTION

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

P/NO : 3828W5S1803

March, 2001

Printed in Korea

Website: http://biz.lgservice.com

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.

SAFETY PRECAUTIONS

(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

1-1

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

ITEM

MODEL

Power Requirement

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

Nameplate Location

Accessories

DESCRIPTION

MB-314XF/MB-314XB

120 Volts AC 60 Hz MICROWAVE 1,400 Watts (12.0) GRILL 1,000 Watts Single phase, 3-wire grounded 1,000 Watts full microwave power (IEC60705) 2,450 MHz 2M246 0 ~ 99 min. 99 sec. 530 (W) x 313 (H) x 394 (D) 348 (W) x 222 (H) x 365 (D)

16.3 kg (approx.)

18.3 kg (approx.) Touch Control System Clock : 1:00 - 12:59 Microwave Power for Variable Cooking Power level

HIGH ----------------------------------------Full power throughout the cooking time 9 (Saute) -------------------------approx. 90% of Full power, 8 (Reheat) --------approx. 80% 7 (Med.-High)--------------------approx. 70%, 6 (Medium) --------approx. 60% 5 (Med.-Low) --------------------approx. 50%, 4 (Defrost) ---------approx. 40% 3 (Low) ---------------------------approx. 30%, 2 (Simmer)--------approx. 20% 1 (Warm)--------------------------approx. 10%

Owner's manual & cooking guide Glass turntable Rotating ring Grill Rack

Back Side

SPECIFICATIONS

• 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.

• DO NOT touch any parts of the control panel circuit. A resulting static electric discharge may damage this P.C.B.

• 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.

GROUNDING INSTRUCTIONS

For personal safety, this appliance must be fully grounded at all times.

In the event of an electrical short circuit, grounding reduces the risk of electrical shock. The plug must be plugged into an outlet that is properly installed and grounded.

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

WARNING

Improper use of the grounding plug can result in a risk of electric shock. Do not, under any circumstances, cut or remove the third ground prong from the power cord plug.

PREFERRED METHOD

ENSURE PROPER GROUND

EXISTS BEFORE USE

10cm

FEATURES

CONTROL PANEL

1. INDICATORS.

2. LOCAL MENU: This menu has been preprogrammed to

cook food automatically by one touch.

3. AUTO GRILL: This feature provides you with the best grill cooking method by selecting menu.

4. GRILL.

5. AUTO COOK: This feature provides you with the best

cooking method by selecting menu.

6. LIGHT MENU: This menu has been preprogrammed to cook food automatically.

7. HOLD WARM: You can keep the food warming by this key.

8. QUICK DEFROST: This feature provides you with the quick

defrosting method for 0.5kg of beef.

9. NUMBER: These used to set for time of day, cooking time & power level, or defrost weight.

10. START: This feature allows oven to begin functioning.

11. COMBI.

12. AUTO REHEAT: This menu has been preprogrammed to

reheat food automatically by selecting menu.

13. AUTO DEFROST: This feature provides you with the best

defrosting method for frozen foods.

14. OPTION: You can select sound ON/OFF, demo ON/OFF

and scroll speed.

15. MICRO: This feature is used for manual cooking or 2 stage

cooking.

16. POWER: You can select the desired power level for

cooking.

17. CLOCK: It is used to set the time of day.

18. ADD 30 MINUTES.

19. STOP/CLEAR: It used to stop oven and clear all entries

except time of day.

4-1

OPERATING INSTRUCTIONS

OVEN CAVITY

DISPLAY WINDOW

DOOR SEAL

CONTROL PANEL

GLASS TURNTABLE

ROTATING RING

SAFETY INTERLOCK

SYSTEM

GRILL RACK

3 4

5 6

7 8

12 13

14 15

17 18

4-2

OPERATING SEQUENCE

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

1. SETTING THE CLOCK

ex.) To set 4:30, touch number key [4],[3], and [0].

NOTE: 1) Clock will operate as long as power is

applied to the oven.

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. ONE TOUCH COOKING

5. TIME COOKING

6. MULTI-STAGE COOKING

7. AUTO WEIGHT DEFROST COOKING

8. CHILD LOCK

This oven has a CHILD LOCK feature

TO SET CHILD LOCK

• Touch the pad

• Touch and hold

PARAR/BORRAR

pad

BLOQUEADO

appear on the display.

TO CANCEL CHILD LOCK

• Touch the pad

• Touch and hold

PARAR/BORRAR

pad

DESBLOQUEADO disappears.

9. OPTION

You can select ON/OFF of beeper, ON/OFF of demo and scroll speed.

• To select sound ON/OFF

• To select scroll speed.

• To select demo ON/OFF.

PARAR/BORRAR

FRIJOLES

PARAR/BORRAR

+30 MÁS

PARAR/BORRAR

1ST STAGE

INICIO

PARAR/BORRAR

DESCONGELADO

AUTO.

NUMBER OF

WEIGHT

INICIO

PARAR/BORRAR

OPCIÓN

INICIO

PARAR/BORRAR

OPCIÓN OPCIÓN

NUMBER

INICIO

PARAR/BORRAR

OPCIÓN OPCIÓN OPCIÓN

INICIO

PARAR/BORRAR

MICRO

NUMBER

POTENCIA

NUMBER INICIO

PARAR/BORRAR

MICRO

NUMBER

POTENCIA

NUMBER

MICRO

NUMBER

INICIO

POTENCIA

NUMBER

2ND STAGE

PARAR/BORRAR

PARAR/BORRAR RELOJ

NUMBER

SCHEMATIC DIAGRAM

4-3

IMPORTANT SAFETY NOTE: THE SHADED AREAS ON THIS SCHEMATIC DIAGRAM INCORPORATE SPECIAL FEATURES

IMPORTANT FOR PROTECTION FROM MICROWAVE RADIATION, FIRE, ELECTRICAL SHOCK, AND

HAZARDS. WHEN SERVICING IT IS ESSENTIAL THAT ONLY MANUFACTURER’S SPECIFIED PARTS

BE USED FOR THE CRITICAL COMPONENTS IN THE SHADED AREAS OF THE SCHEMATIC DIAGRAM.

NOTICE: SINCE THIS IS BASIC SCHEMATIC DIAGRAM, THE VALUES OF COMPONENTS AND

SOME PARTIAL CONNECTIONS ARE SUBJECT TO CHANGE FOR IMPROVEMENT.

20A

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 2.

• Turntable rotates.

• The fan motor rotates and cools the magnetron by

blowing air (coming from the intake on the base-plate).

• The air is also directed into the oven to exhaust the

vapor in the oven through the upper plate.

• Cooking time starts counting down.

• 3.3 volts AC is generated from the filament winding of

the high voltage transformer. This 3.3 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 2 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 the relay 2 is 22 seconds.

WHEN THE DOOR IS OPENED DURING COOKING

• Both the primary switch and relay 2 cut off the 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 fail to open, the fuse opens due to the large current surge caused by the monitor switch activation, which, in turn, stops magnetron oscillation.

4-4

FUSE

H.V.

TRANS-

FORMER

RELAY 2

MICOM CONTROLLER

SECONDARY SWITCH

PRIMARY

SWITCH

MONITOR

SWITCH

PRIMARY

FUSE

SWITCH

MONITOR

SWITCH

RELAY 2

MICOM CONTROLLER

H.V.

TRANS-

FORMER

SECONDARY SWITCH

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.

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 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 (1 in/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

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)

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