Lg Jes735bf Service Manual

MICROW AVE OVEN

SER VICE MANUAL

MODEL: MS-74ML

CAUTION

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

Jan, 2000

Printed in Korea

P/NO:3828W5S1403

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.

E) A microwave leakage check 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.

SAFETY PRECAUTIONS

(Page)

SAFETY PRECAUTIONS

---------------------------------------------------------------------

Inside front cover

SPECIFICATIONS

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1-1

CAUTIONS

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2-1

INSTALLATIONS

------------------------------------------------------------------------------------------------------

3-1

OPERATING INSTRUCTIONS

------------------------------------------------------------------------------------

4-1

FEATURES

------------------------------------------------------------------------------------------------------------------------

4-1

CONTROL PANEL

-------------------------------------------------------------------------------------------------------------

4-1

OPERATING SEQUENCE

----------------------------------------------------------------------------------------------------

4-2

SCHEMATIC DIAGRAM

------------------------------------------------------------------------------------------------------

4-3

CIRCUIT DESCRIPTION

-----------------------------------------------------------------------------------------------------

4-4

SERVICE INFORMATION

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5-1

TOOLS AND MEASURING INSTRUMENTS

---------------------------------------------------------------------------

5-1

MICROWAVE LEAKAGE TEST

--------------------------------------------------------------------------------------------

5-1

MEASUREMENT OF MICROWAVE POWER OUTPUT

-----------------------------------------------------------

5-3

DISASSEMBLY AND ADJUSTMENT

-------------------------------------------------------------------------------------

5-3

INTERLOCK CONTINUITY TEST

------------------------------------------------------------------------------------------

5-7

COMPONENT TEST PROCEDURE

--------------------------------------------------------------------------------------

5-8

TROUBLE SHOOTING

------------------------------------------------------------------------------------------------------

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.

------------------------------------------------------------------------------

8-1

PRINTED CIRCUIT BOARD

-------------------------------------------------------------------------------------------------

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

MS-74ML

120 V 60 Hz
1,050 Watts
Single phase, 3 wire grounded

700 Watts full microwave power (IEC705)
2,450 MHz
2M214 - 39F, 2M218J, 2M254J
0 ~ 99 min. 90 sec.
483 (W) x 285 (H) x 360 (D) mm
312 (W) x 198 (H) x 316 (D) mm

12.5 kg (approx.)
14 kg (approx.)
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

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.

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

FEATURES

CONTROL PANEL

1. INDICATORS

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

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

touch.

4. AUTO DEFROST: Used to select the desired auto
weight defrost programmed with weight pad.

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

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

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

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

except time of day.

9. DISPLAY WINDOW

10. KITCHEN TIMER

4-1

OPERATING INSTRUCTIONS

Oven Frot Plate

Window Door Screen

Door Seal

Display Window
Control Panel

Safety Door Lock System
Turntable

Rotating Ring

Reloj Tiempo

Cocción Automática

10 min 1 min 10 seg

0.1kg1kg

Papas

Vegetales
Frescos

Vegetalesegetales
CongeladosCongelados

Descong

Automático

1.Car1.Carnene

2.Pollo2.Pollo

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

3.Pescado3.Pescado

........

4.Pan4.Pan

....

Nivel de
Cocción

Comenzar

Parar

/

Borrar

1

2
3

4

10

9

5

6
7

8

OPERATING SEQUENCE

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

1. SETTING THE CLOCK

ex) To set 4:35, Press 10 min four times.

Press 1 min three times.
Press 10 sec five times.

NOTE: You can set 12 hour clock.

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. MULTI-STAGE MICROWAVE

COOKING

6. AUTO WEIGHT DEFROST COOKING

7. 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.

8. AUTO COOK

4-2

Stop

Set

clock

Set the

correct time

Stop Start

Stop

Desired

auto cook

category

STOP

STAGE 1

Set

clock

Stop

Stop

Desired

defrost

category

Desired
cooking

weight

Desired

food weight

Start

Start

Start

Stop

Desired

power level

Desired

cooking time

Start

STAGE 2

Stop

Stop

Desired

power level

Desired

cooking time

Desired

power level

Desired

cooking time

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.

RD

BK

PRIMARY

SWITCH

WH

THERMOSTAT

WH

WH

YL

MAGNETRON

RD RD

H.V.

CAPACITOR

H.V. DIODE

FUSE

15A

AC 120V

60Hz

BL

L

N

MICOM

CONTROLLER

F.M.

TRANSFORMER

H.V.

** NOTE : DOOR IS OPENED.

BK : BLACK BL : BLUE YL : YELLOW

RD : RED WH : WHITE PK : PINK

GN : GREEN

O.L.

CN1

PT1

1

2

3

4

5

6

7

8

BK

BK RD

GN

GN

PK

BN

SECONDARY

SWITCH

OVEN

LAMP

MONITOR

SWITCH

TURN

TABLE

MOTOR

FAN

MO TOR

RY1

RY2

GN

WH

WH

BK

T.T.M.

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 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 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 relay 2 is 22 seconds.

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.

4-4

FUSE

H.V.

TRANS-

FORMER

RELAY 2

MICOM CONTROLLER

SECONDARY
SWITCH

MONITOR

SWITCH

N

PRIMARY

SWITCH

L

FUSE

N

L

PRIMARY

SWITCH

MONITOR

SWITCH

RELAY 2

MICOM CONTROLLER

H.V.

TRANS-

FORMER

SECONDARY
SWITCH

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

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
5 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

1

/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)

MEASURING MICROWAVE ENERGY
LEAKAGE

• Pour 275±15 cc 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
(5 cm) 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

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.

5-2

WARNING : AVOID CONTACTING ANY

HIGH VOLTAGE PARTS
(Magnetron, H.V. Transformer,
H.V. Capacitor, H.V. Cable Ass’y,
H.V. Circuit Protector)

• 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 190mm.

• 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 :

4187 x (∆T)

T

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.

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

WATER LOAD

TURNTABLE

MEASUREMENT OF MICROWAVE POWER OUTPUT

P =

DISASSEMBLY AND ADJUSTMENT

D. DOOR GROSS ASSEMBLY REMOVAL

1) Open the door.

2) Remove the choke cover very carefully with a flat-blade
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. (with a 275 ml water
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.

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.

5-4

Remove choke cover

Remove door

H.V.
Transformer

Suction
Guide

H.V.
Diode

H.V.
Capacitor

Fan Motor
ASS’Y

Noise Filter

H. AIR DUCT ASSEMBLY REMOVAL

1) Disconnect the leadwire from the lamp.

2) Remove the mounting screw to the latch board.

I. MAGNETRON REMOVAL

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

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

3) 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.

NOTE:

1. Remove the wire lead from the turntable motor

VERY CAREFULLY.

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

removing.

5-5

Waveguide

Magnetron

Magnetron
Gasket

Magnetron

Dome
Waveguide

Bracket

Wire Leads

Turntable Motor

K. PCB ASSEMBLY REMOVAL

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

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 less
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

Key Membrane

Control Panel

PCB Sub ASS'Y

ADJUSTMENT
DIRECTION

SECONDARY
SWITCH

MONITOR
SWITCH

PRIMARY
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.

5-7

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

COMPONENTS TEST PROCEDURE RESULTS

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

Primary
Switch

Monitor
Switch

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

connected correctly.

INTERLOCK CONTINUITY TEST

Secondary
Switch

COM

COM

COM

NO

NC

NO

5-8

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)

• Between Filament terminal

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

• Filament to chassis

Approx.: 2.5 Ω
Approx.: 110 Ω
Less than: 0.4 Ω

Normal: ∞
Normal: ∞

Normal: Less than 1 Ω

Normal: ∞

PRIMARY
TERMINAL

SECONDARY
TERMINAL

FILAMENT
WINDING
TERMINAL

COMPONENT TEST PROCEDURE

5-9

COMPONENTS TEST PROCEDURE RESULTS

HIGH VOLTAGE
CAPACITOR

HIGH VOLTAGE
DIODE

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

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)

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

Normal: Momentarily indicates

several ohms, and
then gradually returns
to infinite.

Normal: ∞

Normal: Continuity.
Abnormal: ∞

Normal: ∞
Abnormal: Continuity.

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.

Antenna
Gasket

Chassis

Filament
Terminals

COMPONENTS TEST PROCEDURE RESULTS

5-10

RELAY 2

FAN MOTOR
(Wire leads removed)

TURNTABLE
MOTOR
(Wire leads removed)

Check for continuity of relay 2 with an
ohm-meter.
(Remove wire leads from relay 2 and
operate the unit.)

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

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

POWER
LEVEL

20% 6 sec 16 sec
40% 10 sec 12 sec
60% 14 sec 8 sec
80% 18 sec 4 sec

100% 22 sec 0 sec

Normal:
A~B : Approx. 65 ~ 80 ohm
B~C : Approx. 10 ~ 30 ohm
A~C : Approx. 85 ~ 105 ohm

Abnormal: Infinite or several

ohm.

Normal: Approx. 2-4 KΩ
Abnormal: ∞ or several Ω

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.

Relay 1

Relay 2

Power
Transformer

A(RD)

B(BK)

C(WH)

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.

5-11

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 circuit on the PCB 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. (Micom model only)

CONDITION

Microwave oven

does not work.

Inserting many plug into one
plug outlet and using
them at the same time
(blown fuse or breaker)

Microwave oven plug is not
inserted tightly.

Output power is too low. Low AC input voltage.

Food temperature is too low.

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

Sparks occur.

Inconsistent intensity of
microwave by their
characteristics.

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.

Uneven cooking.

Ceramic ware trimmed in
gold or silver power is used.

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.

CAUSE REMEDY

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.

5-12

(TROUBLE 1)

The following visual conditions indicate a probable defective control circuit.

CONDITION CHECK RESULT CAUSE REMEDY

1. No input can be
programmed.

Continuity

No continuity

Defective PCB
assembly.

Loose
connection.

Replace PCB
assembly.

Connect them
tightly.

Check the conn­ection between
membrane key
assembly and
PCB assembly.

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.

Everything works
as specified.

Still have trouble.

Defective key
membrane
assembly.

Defective PCB
assembly.

Replace key
membrane
assembly.

Replace PCB
assembly.

Replace key
membrane
assembly and
check operation.

5-13

CONDITION CHECK RESULT CAUSE REMEDY

1. Fuse blows. Continuity.

No continuity.

Continuity.

Shorted contact at
the primary switch.

Replace fuse,
primary, monitor
switches, and
RELAY(RY2) of
P.C.B Assembly.

No continuity.

Normal.

Defective high
voltage capacitor.

Replace high
voltage capacitor.

Fuse blows again

Defective high volt­age transformer.

Replace high volt­age transformer.

Malfunction of the
monitor switch.

Replace fuse,
primary, monitor
switches, and
RELAY(RY2) of
P.C.B Assembly.

Check continuity
of monitor
switch (with
door closed).

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.

Replace fuse

2. Fuse does not
blow.

No continuity.

Continuity.

No continuity.

Defective power
supply cord.

Replace power
supply cord.

Defective
thermostat.

Replace
thermostat.

Check continuity
of thermostat.

Check continuity
of power supply
cord.

(TROUBLE 2)

Oven does not operate at all; Display window does not display any figures,

and no input is accepted.

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

5-14

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.

No continuity.

Continuity.

Continuity

Defective PCB
assembly.

Loose connection.

Replace PCB
assembly.

Connect them
tightly.

No continuity

Abnormal

Check fan motor.

Defective fan motor. Replace fan motor.

Abnormal

Normal

Check oven lamp.

Defective oven lamp. Replace oven lamp.

Defective
secondary switch.

Replace
secondary switch.

Check continuity
of secondary
switch (with
door closed).

Check the con­nection between
CN1 connector
and PCB
assembly.

(TROUBLE 3)

Display shows all figures set, but oven does not start cooking while desired

program times are set and START pad is touched.

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

NOTE :

Simple test of power output-conducted by heating one liter water for one min. if available.
Minimum 8.5°C temperature rise is normal condition.

CONDITION CHECK RESULT CAUSE REMEDY

Output is low

Lower than 90% of
rating voltage.

Normal

Abnormal

Defective PCB
assembly.

Replace PCB
assembly.

Normal

Abnormal

Measure the
output power.

Defective
magnetron.

Replace
magnetron.

Decrease in power
source voltage
with load.

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

Check the
power source
voltage.

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

5-15

CONDITION CHECK RESULT CAUSE REMEDY

No microwave
oscillation.

No continuity.

Continuity.

Abnormal

Defective high
voltage
transformer.

Replace high
voltage
transformer.

Normal

Defective PCB
assembly.

Replace PCB
assembly.

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

Check high vol­tage transformer.

Abnormal

Defective

circuit

protector.

Replace

circuit

protector.

Normal

Check circuit
protector.

Abnormal

Defective high
voltage capacitor.

Replace high
voltage capacitor.

Normal

Check high vol­tage capacitor.

Abnormal

Defective high
voltage diode.

Replace high
voltage diode.

Normal

Check high vol­tage diode.

Abnormal

Defective
magnetron.

Replace
magnetron.

Check
magnetron.

(TROUBLE 5)

No microwave oscillation even though oven lamp and fan motor run.

(Display operates properly)

5-16

Output is full power
when you set lower
power level.

Abnormal.

Defective PCB
assembly.

Replace PCB
assembly.

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

NOTE : • Make sure the wire leads correct position.

• When Removing the wire leads from the parts, be sure to grasp the connector, not the wires.

• When removing the magnetron, be sure to install the magnetron gasket in the correct position

and in good condition.

CONDITION CHECK RESULT CAUSE REMEDY

(TROUBLE 5)

No microwave oscillation even though oven lamp and fan motor run.

(Display operates properly)

DOOR PARTS

LATCH BOARD PARTS

CONTROL PANEL PARTS

INTERIOR PARTS

BASE PLATE PARTS

OVEN CAVITY PARTS

6-1

EXPLODED VIEW

INTRODUCTION

#EV#

MODEL : MS-74ML

6-2

14970A

14026A

13552A

13536A

13213A

13720D

13352A

13581A

DOOR PARTS

#EV#

6-3

WTP018

26638A

23572A

23550D

24930D

24781M

268711

CONTROL PANEL PARTS

#EV#

6-4

33112U

WTT021

36549S

WTP013

33052M

33390G

35889A

OVEN CAVITY PARTS

#EV#

6-5

43501A

43500A

466001

WSZ085

466003

466002

44510A

LATCH BOARD PARTS

#EV#

6-6

WSZ002

WSZ002

WTT028

WSZ062

WSZ002

WTT037

56324A

55262A

55900A

56549F

56411A

56930V

568771

54974S

56912B

INTERIOR PARTS

#EV#

6-7

BASE PLATE PARTS

#EV#

56170D

WSZ002

63302A

63303A

WTT021

65006B

50CZZH

54810C

56851D

WSZ002

65006B

8-1

SCHEMATIC DIAGRAM OF P.C.B

8-2

PRINTED CIRCUIT BOARD