LG MS-0747C Service Manual

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MICROWAVE OVEN

SERVICE MANUAL

MODEL: MS-0747C

CAUTION

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

P/NO : MFL34456302

May, 2007

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

4-1

4-1

4-2

4-3

4-4

5-1

5-1

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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SCHEMATIC DIAGRAM OF P.C.B.

PRINTED CIRCUIT BOARD

P.C.B. PARTS LIST

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5-3

5-7

5-8

5-12

6-1

7-1

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8-1

8-2

9-1

SPECIFICATIONS

ITEM

MODEL

Power Requirement

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

DESCRIPTION

MS-0747C

120 Volts AC 60 Hz
1000 Watts
Single phase, 3 wire grounded

700 Watts full microwave power (IEC60705)
2450 MHz
2M213 - 240GP
10 sec.~ 99 min. 50 sec
455 (W)x 284 (H)x 320 (D)mm
327 (W)x 202 (H)x 286 (D)mm

9.5 kg (approx.)
11 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

Rating Label Location

Owner's manual

Accessories

Glass turntable

Rotating ring

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

Back Side

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).

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.

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

TEMPORARY METHOD
(ADAPTER PLUGS NOT
PERMITTED IN CANADA)

ALIGN LARGE
PRONGS/SLOTS

10cm

ENSURE PROPER GROUND
AND FIRM CONNECTION
BEFORE USE

3-1

OPERATING INSTRUCTIONS

Oven Front Plate

Window Door Screen

Door Seal

Safety Door Lock System
Glass Turntable

Rotating Ring

Control Panel

FEATURES

CONTROL PANEL

1. INDICATORS

2. ONE TOUCH CONTROL: Used to cook the foods

listed by one touch.

1

2

34

5

6

7

3. Q-DEFROST

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

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 the desired power level for

cooking.

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

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

8

9

4-1

OPERATING SEQUENCE

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

1. SETTING THE CLOCK

PARAR/BORRAR

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

NOTE: 1) This is a 12 hour clock.

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

RELOJ NUMBER RELOJ

2. CANCEL FUNCTION

Touch the
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

pad whenever you need to

3. ONE TOUCH COOKING

PARAR/BORRAR

POPCORN

4. MICROWAVE COOKING

PARAR/BORRAR

TIEMPO NUMBER

NUMBER

INICIO

POTENCIA

5. TIME COOKING

6. MULTI-STAGE MICROWAVE COOKING

1ST STAGE

PARAR/BORRAR

2ND STAGE

1ST STAGE

TIEMPO NUMBER

NUMBER

TIEMPO NUMBER

NUMBER

INICIO

POTENCIA

POTENCIA

7. AUTO DEFROST COOKING

PARAR/

BORRAR

DESCONGELADO

AUTOMÁTICO

NUMBER OF

WEIGHT

INICIO

8. CHILD LOCK

This oven has a CHILD LOCK feature
TO SET CHILD LOCK

• Touch the 0 pad

• Touch and hold 0 pad L appear on
the display.

TO CANCEL CHILD LOCK

• Touch the 0 pad

• touch and hold 0 pad L disappears.

PARAR/BORRAR

TIEMPO NUMBER

NUMBER

INICIO

POTENCIA

4-2

SCHEMATIC DIAGRAM

4-3

CIRCUIT DESCRIPTION

L

FUSE

H.V.

TRANS-

FORMER

RELAY 2

MICOM CONTROLLER

SECONDARY
SWITCH

PRIMARY

SWITCH

N

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.

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)

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.

FUSE

PRIMARY

SWITCH

• 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.

generated in the secondary of the high voltage

• A high voltage of approximately 2100 volts AC is

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.

L

N

RELAY 2

MICOM CONTROLLER

MONITOR

SWITCH

TRANS-

FORMER

SECONDARY
SWITCH

H.V.

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/cm

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
5 mW/cm2. Always start measuring of an unknown field
to assure safety for operating personnel from radiation
leakage.

2

and should repair any

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)

1

/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

WATER LOAD

TURNTABLE

MEASUREMENT OF MICROWAVE POWER OUTPUT

• Microwave power output measurement is made with
the microwave oven supplied at its rated voltage and
operated at its maximum microwave power setting with
a load of (1000 ± 5)g of potable water.

• The water is contained in a cylindrical borosilicate glass
vessel having a maximum material thickness of 3 mm
and an outside diameter of approximately 190 mm.

• The oven and the empty vessel are at ambient
temperature prior to the start of the test.

• The initial temperature (T1) of the water is (10±2)°C.It
is measured immediately before the water is added to
the vessel. After addition of the water to the vessel,
the load is immediately placed on the center of the
turntable which is in the lowest position and the
microwave power switched on.

• The time T for the temperature of the water to rise by a
value ∆T of (10±2)°K is measured, where T is the time
in seconds and ∆T is the temperature rise. The initial
and final water temperatures are selected so that the
maximum difference between the final water
temperature and the ambient temperature is 5°K.

• The microwave power output P in watts is calculated
from the following formula :

2

- T0) X M

T

P =

4187 X (∆T) + 0.55 X (T

2

• T

: Temperature after heating

0

: Temperature after bown

• T

• M : Weight of bowl

is measured while the microwave generator is
operating at full power. Magnetron filament heat-up
time is not included. (about 3 sec)

• The water is stirred, to equalize temperature throughout
the vessel, prior to measuring the final water
temperature.

• Stirring devices and measuring instruments are
selected in order to minimize addition or removal of
heat.

DISASSEMBLY AND ADJUSTMENT

A. OUTER CASE REMOVAL

1) Disconnect the power supply cord from the outlet.

2) Remove the screws from the rear and along side
edges of the case.
The outer case must be moved backward to be lifted
off.

B. POWER SUPPLY CORD

1) Remove the outer case.

2) Disconnect two terminals, and remove one screw of
the earth terminal.

CAUTION: DISCHARGE THE HIGH VOLTAGE

CAPACITOR BEFORE SERVICING

(refer to page 2-1)

C. CONTROL PANEL ASSEMBLY

1) Disconnect the leadwire from the PCB SUB ASS’Y.

2) Remove the screws for the earth and securing the
control panel.

3) Lift control panel ASS’Y from the oven by the tab

unhooked.

5-3

D. DOOR GROSS ASSEMBLY REMOVAL

Suction
Guide

Fan Motor
ASS'Y

H.V.
Transformer

H.V.
Capacitor

1) Open the door.

2) Pull out the door protector very carefully with a flat­blade screwdriver.

CAUTION : Be careful not to damage door seal plate

by screwdriver.

3) Lift up and push the door.

NOTE:

1. After replacing the door, be sure to check that the

primary switch, monitor switch, and secondary switch
operate normally.

2. After replacing the door, check for microwave energy

leakage with a survey meter. Microwave energy must
be below the limit of 5 mW/cm
load)

3. When mounting the door assembly to the oven

assembly, be sure to adjust the door assembly parallel
to the chassis. Also adjust so the door has no play
between the inner door surface and oven frame
assembly. If the door assembly is not mounted
properly, microwaves may leak from the clearance
between the door and the oven.

Remove door assembly

2

. (with a 275 ml water

E. HIGH VOLTAGE TRANSFORMER

REMOVAL

1) Discharge the high voltage capacitor.

2) Disconnect the leadwire from magnetron, high voltage
transformer, and capacitor.

3) Remove the screw holding the high voltage
transformer to the baseplate.

F. FAN MOTOR ASSEMBLY REMOVAL

1) Discharge the high voltage capacitor.

2) Disconnect the leadwire from fan motor, noise filter

and high voltage capacitor.

3) Remove the two screws holding the the suction guide

ASS’Y to the oven cavity and remove the high voltage
diode earth screw.

4) Remove the screw of the capacitor bracket.

5) Remove the two screws holding the fan motor ASS’Y

to the suction guide ASS’Y.

G. HIGH VOLTAGE CAPACITOR AND

DIODE REMOVAL

1) Discharge the high voltage capacitor.

2) Disconnect the leadwire from fan motor, noise filter

and high voltage capacitor.

3) Remove the screw holding the suction guide ASS’Y to

the oven cavity and remove the high voltage diode
earth screw.

4) Remove the screw holding the high voltage capacitor

bracket.

Remove door assembly

5-4

H. AIR DUCT ASSEMBLY REMOVAL

Waveguide

Air Duct

Magnetron
Gasket

Magnetron

Dome

Waveguide
Bracket

Magnetron

1) Disconnect the leadwire from lamp, A.C Relay and
monitor resistor and magnetron.

2) Remove the screw to the magnetron cavity.

I. MAGNETRON REMOVAL

1) Disconnect the leadwire from the high voltage
transformer and high voltage capacitor.

2) Remove the air duct ASS’Y.

3)

Carefully remove the mounting screws holding the
magnetron and the waveguide.

4)

Remove the magnetron ASS’Y until the tube is
clear from the waveguide.

NOTE:

1. When removing the magnetron, make sure its
dome does not hit any adjacent parts, or it may be
damaged.

2. When replacing the magnetron, be sure to install
the magnetron gasket in the correct position and
be sure that the gasket is in good condition.

3. After replacing the magnetron, check for microwave
leakage with a survey meter around the
magnetron. Microwave energy must be below the
limit of 5 mW/cm2. (With a 275 ml. water load).

Make sure that gasket is rigidly attached to the
magnetron. To prevent microwave leakage,

tighten the mounting screws properly, making sure
there is no gap between the waveguide and the
magnetron.

J. REMOVING THE TURNTABLE MOTOR

1) Remove the turntable.

2) Remove the turntable shaft VERY CAREFULLY.

3) Lay the unit down on its back.

4) Remove the turntable motor cover.
The turntable base cover is easily removed by
pinching the six parts with a wire cutting.

5) Disconnect the leadwire from the turntable motor
terminals.

6) Remove the screw securing the turntable motor to
the oven cavity ASS’Y

7) After repairing the motor, rotate the removed
turntable motor cover.

8) Fit the turntable motor cover’s projecting part to the
base plate slit.

9) The taptite screw shall be used when a turntable
motor cover is secured with a screw.

NOTE:

1. Remove the wire lead from the turntable motor
VERY CAREFULLY.

2. Be sure to grasp the connector, not the wires, when
removing

Taptite Screw

5-5

K. PCB ASSEMBLY REMOVAL

Key Membrane

Control Panel

PCB Sub Asm

1) Remove the control panel assembly from the
cavity. (Refer to control panel assembly removal
on previous page.)

2) Remove screws which hold the PCB SUB ASS’Y to
the control panel.

3) Disconnect the flat cable from the PCB SUB
ASS’Y and take off the PCB SUB ASS’Y.

L. INTERLOCK SYSTEM

1) INTERLOCK MECHANISM
The door lock mechanism is a device which has
been specially designed to eliminate completely
microwave activity when the door is opened during
cooking and thus to prevent the danger resulting
from the microwave leakage.

2) MOUNTING OF THE PRIMARY/MONITOR/
SECONDARY SWITCHES TO THE LATCH
BOARD

ADJUSTMENT

DIRECTION

PRIMARY

SWITCH

MONITOR

SWITCH

SECONDARY

SWITCH

3) INSTALLATION AND ADJUSTMENT OF THE
LATCH BOARD TO THE OVEN ASSEMBLY

• Mount the latch board to the oven assembly.

• Adjust the latch board in the arrow direction so that

oven door will not have any play in it when the door
is closed.

• Tighten the mounting screw.

• Check for play in the door by pushing the door

release button. Door movement should be les
than 0.5 mm. (1/64 inch)

Don't push the door release button while making
adjustment. Make sure that the latch moves
smoothly after adjustment are completed and that
the screws are tight. Make sure the primary, monitor,
and secondary switches operate properly by
following the continuity test procedure.

5-6

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. PRIMARY INTERLOCK SWITCH TEST

When the door release button is depressed slowly
with the door closed, an audible click should be
heard at the same time or successively at
intervals. When the button is released slowly, the
latches should activate the switches with an
audible click.
If the latches do not activate the switches when
the door is closed, the switches should be a
adjusted in accordance with the adjustment
procedure. Disconnect the wire lead from the
primary switch. Connect the ohmmeter leads to
the common (COM) and normally open (NO)
terminal of the switch. The meter should indicate
an open circuit in the door open condition.
When the door is closed, the meter should
indicate a closed circuit.
When the primary switch operation is abnormal,
make the necessary adjustment or replace the
switch only with the same type of switch.

B. SECONDARY INTERLOCK SWITCH TEST

Disconnect the wire lead from the secondary
switch.
Connect the ohmmeter leads to the common
(COM) and normally open (NO) terminals of the
switch. The meter should indicate a open circuit in
the door open condition. When the door is closed,
meter should indicate an closed circuit. When the
secondary switch operation is abnormal, make the
necessary adjustment or replace the switch only
with the same type of switch.

C. MONITOR SWITCH TEST

Disconnect the wire lead from the monitor switch.
Connect the ohmmeter leads to the common
(COM) and normally closed (NC) terminals of the
switch. The meter should indicate closed circuit in
the door open condition. When the door is closed,
meter should indicate an open circuit. When the
monitor switch operation is abnormal, replace with
the same type of switch.

NOTE: After repairing the door or the interlock
system, it is necessary to do this continuity
test before operating the oven.

COMPONENTS TEST PROCEDURE RESULTS

SWITCHES Check for continuity of the Door Door
(Wire leads removed) switch with an Ohm-meter open close

Primary
Switch

Monitor
Switch

Secondary
Switch

NOTE : After checking for the continuity of switches, make sure that are

connected correctly.

COM

COM

COM

NO

NC

NO

5-7

PRIMARY
TERMINAL

SECONDARY
WINDING

FILAMENT
WINDING
TERMINAL

COMPONENT TEST PROCEDURE

CAUTIONS

1. DISCONNECT THE POWER SUPPLY CORD FROM THE OUTLET WHENEVER REMOVING THE
OUTER 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. (SEE PAGE 2-1)

2. ALL OPERATIONAL CHECKS WITH MICROWAVE ENERGY MUST BE DONE WITH A LOAD (1 LITER
OF WATER IN CONTAINER) IN THE OVEN.

COMPONENTS TEST PROCEDURE RESULTS

HIGH VOLTAGE
TRANSFORMER
(Wire leads removed)

MAGNETRON
(Wire leads removed)

1. Measure the resistance.
(Ohm-meter scale: Rx1)

• Primary winding

• Secondary winding

• Filament winding

2. Measure the resistance.
(Ohm-meter scale: Rx1000)

• Primary winding to ground

• Filament winding to ground

1. Measure the resistance.
(Ohm-meter scale: Rx1)

• Filament terminal

2. Measure the resistance.
(Ohm-meter scale: Rx1000)

• Filament to chassis

5-8

Approx.: 1.4 Ω
Approx.: 90 Ω
Less than: 01 Ω

Normal: ∞
Normal: ∞

Normal: Less than 1 Ω

Normal: ∞

COMPONENTS TEST PROCEDURE RESULTS

Antenna
Gasket

Chassis

Filament

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.

HIGH VOLTAGE
CAPACITOR

HIGH VOLTAGE
DIODE

Measure the resistance.
(Ohm-meter scale: Rx1000)

• Terminal to terminal.

Measure the resistance.
(Ohm-meter scale: Rx1000)

• Terminal to case.

Measure the continuity (Forward).
(Ohm-meter scale: Rx10000)

Normal: Momentarily indicates

several ohms, and then
gradually returns to
infinite.

Normal: ∞

Normal: Continuity.
Abnormal: ∞

NOTE :
Some inexpensive meters
may indicate infinite
resistance in both direction.

Measure the continuity (Reverse).
(Ohm-meter scale: Rx10000)

5-9

Normal: ∞
Abnormal: Continuity.

COMPONENTS TEST PROCEDURE RESULTS

FUSE

THERMAL
CUT-OUT

Disconnect the 7 pin
connector from P.C.B.
(Refer to schemetic diagram)

Check for continuity of the fuse with an

Normal Abnormal

multi-meter.

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. Replace just the fuse if the switches operate normally.

0°C~Approx.90°C Approx.90°C

Check for P.C.B. connector.

Cooking Start OFF

RELAY 2 OF P.C.B.
(Wire leads removed.)
Note: Relay
Relay 1: Fan motor

Turntable motor
Oven lamp

Relay 2: Microwave

13 5

Cooking Start OFF

Relay 1

Relay 2

5-10

COMPONENTS TEST PROCEDURE RESULTS

A

B

C

FAN MOTOR
(Wire leads removed)

TURNTABLE
MOTOR
(Wire leads removed)

Measure the resistance.
(Ohm-meter scale: R x 100)

Measure the resistance.
(Ohm-meter scale: R x 1000)

Normal:

A ~ B A ~ C

40 ~ 60 300~500

Abnormal: ∞ or several

Normal: Approx. 100~200 Ω
Abnormal: ∞ or several

NOTE : • A MICROWAVE LEAKAGE TEST MUST ALWAYS BE PERFORMED WHEN THE UNIT IS

SERVICED FOR ANY REASON.

• MAKE SURE THE WIRE LEADS ARE IN THE CORRECT POSITION.

• WHEN REMOVING THE WIRE LEADS FROM THE PARTS, BE SURE TO GRASP THE
CONNECTOR, NOT THE WIRES.

5-11

TROUBLE SHOOTING

WHEN YOU GET A COMPLAINT FROM YOUR CUSTOMER, EVALUATE THE COMPLAINT CAREFULLY. IF
THE FOLLOWING SYMPTOMS APPLY, PLEASE INSTRUCT THE CUSTOMER IN THE PROPER USE OF THE
MICROWAVE OVEN. THIS CAN ELIMINATE AN UNNECESSARY SERVICE CALL.

CAUTIONS

1. Check grounding before checking for trouble.

2. Be careful of the high voltage circuit.

3. Discharge the high voltage capacitor. (See page 2-1)

4. When checking the continuity of the switches or of the high voltage transformer, disconnect one lead wire
from these parts and then check continuity with the AC plug removed. To do otherwise may result in a
false reading or damage to your meter.

5. Do not touch any part of the circuitry on the digital programmer circuit since static electric discharge may
damage this control panel.

Always touch yourself ground while working on this panel to discharge any static charge built up in your

body.

CONDITION

Microwave oven

does not work.

Output power is too low. Low AC input voltage.

Sparks occurring.

Inserting many plug into one
plug outlet and using
them at the same time
(causes overloading).

Microwave oven plug is not
inserted tightly.

Food temperature is too low.

Using metallic ware and
allowing it to touch the oven
wall.

Ceramic ware trimmed in
gold or silver powder is used.

CAUSE REMEDY

Avoid using other electrical
appliances when you use the
microwave oven.

Insert microwave oven plug
securely.

Use the microwave oven at
adequate line voltage.

This may not be a defect.
It is possible that the food
should be cooked for a
longer time period.

Do not use metallic ware for
cooking except where noted
in the cooking guide.

Do not use any type of
cookware with metallic
trimming.

Uneven cooking.

Turntable drags or makes
noise.

Inconsistent intensity of
microwave by their
characteristics.

Excessive weight on tray or
improperly balanced.

5-12

1. Wrap the thinner part with
aluminum foil.

2. Use plastic wrap or lid.

3. Stir once or twice while cooking
soup, cocoa or milk, etc.

Distribute food evenly. Cook
smaller portions and,or use
lighter weight cookware.

(TROUBLE 1) The following visual conditions indicate a probable defective control circuit.

1. Incomplete segments.

• Segment missing.

• Partial segment missing.

• Digit flickering (NOTE: Slight flickering is normal.)

2. Colon does not turn on or blink.

3. A distinct change in the brightness of one or more numbers in display.

4. One or more digits in the display are not lighting.

5. Display indicates a number different from one touched, for example, key in 5 and 3 appears in the display.

6. Specific numbers (for example 7 or 9) will not display when key pad is touched.

7. Display does not count down with time blinking or up with clock operation.

8. Display obviously jumps in time while counting down.

9. Display counts down too fast while cooking.

10. Each indicator light does not turn on after setting cooking cycle.

11. Display time of day does not reappear when cooking is finished.

12. Beep sound is not heard when correct key is touched.

CONDITION CHECK RESULT CAUSE REMEDY

1. No input can be
programmed.

2. Some inputs
cannot be
programmed.

3. Display shows a
number or figure
different from one
touched.

4. Random
programming
when touching
other pads.

5. Display is fixed
at some figure
and can not
accept any
input.

Check the conn­ection between
membrane key
assembly and
PCB assembly.

Replace key
membrane
assembly and
check operation.

Continuity.

No continuity.

Everything works
as specified.

Still have trouble.

Defective PCB
assembly.

Loose
connection.

Defective key
membrane
assembly.

Defective PCB
assembly.

Replace PCB
assembly.

Connect them
tightly.

Replace key
membrane
assembly.

Replace PCB
assembly.

5-13

(TROUBLE 2) Oven does not operate at all ; Display window does not display any figures,

and no input is accepted.

CONDITION CHECK RESULT CAUSE REMEDY

1. Fuse blows. Continuity.

Check continuity
of monitor
switch (with
door closed).

Replace fuse

Check continuity
of primary
switch (with
door opened).

Disconnect one
side of the wire
lead connected
from transformer
to the high
voltage
capacitor and
operate the unit.

No continuity.

Continuity.

No continuity.

Normal.

Fuse blows again

Malfunction of the
monitor switch.

Shorted contact at
the primary switch.

Defective high
voltage capacitor.

Defective high volt­age transformer.

Replace primary
and monitor
switches.

Replace primary
and monitor
switches.

Replace high
voltage capacitor.

Replace high volt­age transformer.

NOTE : All these switches must be replaced at the same time. Refer to page 5-6, 5-7

2. Fuse does not
blow.

Check continuity
of magnetron
thermostat.

Check continuity
of power supply
cord.

No continuity.

Continuity.

No continuity.

Defective mag­netron thermostat.

Defective power
supply cord.

5-14

Replace mag­netron thermostat.

Replace power
supply cord.

(TROUBLE 3) Display shows all figures set, but oven does not start cooking while

desired program times are set and START pad is touched.

CONDITION CHECK RESULT CAUSE REMEDY

1.Setting time does

not count down
when touching
START pad.

2. Fan motor or
oven lamp
do not turn
on.

Check continuity
of secondary
switch (with
door closed).

Check the con­nection between
connector and
P.C.B assembly.

Check fan motor.

Check oven lamp.

No continuity.

continuity.

No continuity.

Continuity.

Abnormal.

Abnormal.

Normal.

Defective
secondary switch.

Defective P.C.B
assembly.

Loose connection.

Defective fan
motor.

Defective oven
lamp.

Replace
secondary switch.

Replace P.C.B
assembly.

Connection then
tightly.

Replace fan
motor.

Replace oven
lamp.

(TROUBLE 4) Oven seems to be operation but little heat is produced in oven load.

CONDITION CHECK RESULT CAUSE REMEDY

Output is low.

NOTE: Simple test of power output-conducted by heating one liter water for one min. if available.

Minimum 8.5

Check the
power source
voltage.

Disconnect the
wire leads from
relay 2 and check
on and off time
with multitester.

Measure the
output power.

o

C temperature rise is normal condition.

Lower than 90% of
rating voltage.

Normal.

Abnormal.

Normal.

Abnormal.

Decrease in power
source voltage
with load.

Defective P.C.B
assembly.

Defective
magnetron.

Suggest customer
contact local
electric power
utility co. or
qualified
electrician.

Replace P.C.B
assembly.

Replace
magnetron.

5-15

(TROUBLE 5)

No microwave oscillation even though oven lamp and fan motor run
(Display operates properly)

CONDITION CHECK RESULT CAUSE REMEDY

No microwave
oscillation.

Disconnect the
wire leads from
relay 2 and
check continuity
of relay2.
(Operate the
unit)

Check H.V.
transformer.

Check H.V.
capacitor.

Check H.V.
diode.

No continuity.

Continuity.

Abnormal

normal

Abnormal

normal

Abnormal

Defective P.C.B
assembly

Defective high
voltage
transformer.

Defective high
voltage capacitor.

Defective high
voltage Diode.

Replace P.C.B
assembly

Replace high
voltage
transformer .

Replace high
voltage capacitor.

Replace high
voltage Diode.

Check
Magnetron.

Check
Protector Diode.

normal

Abnormal

normal

Abnormal

5-16

Defective
magnetron.

Defective
Protector Diode.

Replace
magnetron .

Replace
Protector Diode .

(TROUBLE 6) Oven does not cook properly when programmed for the set power level

(Operates properly on HIGH)

CONDITION CHECK RESULT CAUSE REMEDY

Output is full when

you set lower
power level.

Disconnect the
wire leads from
relay 2 and check
continuity relay 2.
(Operate the unit)

Abnormal.

Defective P.C.B.
assembly.

Replace P.C.B.
assembly.

5-17

#EV#

EXPLODED VIEW

INTRODUCTION

MODEL: MS-0747C

DOOR PARTS

CONTROL PANEL PARTS

OVEN CAVITY PARTS

INTERIOR PARTS

BASE PLATE PARTS

LATCH BOARD PARTS

6-1

#EV#

DOOR PARTS

13581A

13552A

13536A

13213A

13720D

14890A

14026A

14970A

6-2

#EV#

CONTROL PANEL PARTS

24781M

268711

23572A

23506A

WTT021

6-3

#EV#

OVEN CAVITY PARTS

33052A

33112U

WTT021

WTT010

33390G

36549S

34370T

35889A

WTP013

6-4

#EV#

LATCH BOARD PARTS

43500A

WSZ085

466001

43501A

466003

44510A

6-5

466001

#EV#

INTERIOR PARTS

WSZ002

56411A

56930V

WSZ002

56912B

56324A

50CZZH

50FZZA

55006F

WTT028

WTT037

56549F

55900A

54974S

WEB001

56851D

WEB001

54810C

55262A

WTT028

948501

568771

6-6

#EV#

BASE PLATE PARTS

56170D

63303A

65006B

63302A

WTT021

WSZ002

6-7

SCHEMATIC DIAGRAM OF P.C.B

8-1

PRINTED CIRCUIT BOARD

8-2