LG LTRM1240xx Service Manual

MICROWAVE OVEN

SERVICE MANUAL

MODEL: LTRM1240SW

LTRM1240SB
LTRM1240ST

CAUTION

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

Website http://us.lgservice.com

P/NO : 3828W5S6018

July, 2004

Printed in Korea

-1-

This device is to be serviced only by properly qualified service personnel.
Consult the service manual for proper service procedures to assure continued safety operation and for precautions to be taken to
avoid possible exposure to excessive microwave energy.

PRECAUTIONS TO BE OBSERVED BEFORE AND DURING
SERVICING TO AVOID POSSIBLE EXPOSURE TO
EXCESSIVE MICROWAVE ENERGY

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

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

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

and sealing surfaces (arcing, wear, and other damage), (4) damage to or loosening of hinges and latches, (5)

evidence of dropping or abuse.

C) Before turning on microwave power for any service test or inspection within the microwave generating

compartments, check the magnetron, wave guide or transmission line, and cavity for proper alignment,

integrity, and connections.

D) Any defective or misadjusted components in the interlock, monitor, door seal, and microwave generation and

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

the oven is released to the owner.

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

on each oven prior to release to the owner.

SAFETY PRECAUTIONS

CAUTION

MICROWAVE RADIATION

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

-2-

MECHANICAL SERVICE INFORMATION

TABLE OF CONTENTS

1. Safety precautions

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

Inside front cover

2. Specifications

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

3

3. Cautions

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

4

4. Installations

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

5

5. Overall Circuit Diagram

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

6-7

6. Operating Procedures

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

8-9

7. Procedure for Measuring Microwave Energy Leakage

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

10-11

8. Disassembly Instructions ............................................................................................................................ 12-15

9. Interlock Continuity Test ............................................................................................................................. 16

10. Test and Checkout Procedures,and Troubleshooting

A. Test Procedures

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

17-20

B. Checkout Procedures

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

21-23

C. Troubleshooting

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

24-29

11. Exploded View

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

30-37

12. Replacement Parts List

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

38-44

FOREWORD

Read this Manual carefully. Failure to adhere to or observe the information in this Manual may result in exposing yourself to
the Microwave Energy normally contained within the oven cavity.

-3-

This microwave oven is designed for household use only.

It is not recommended for commercial purposes.

DESCRIPTION

LTRM1240SW

LTRM1240SB

LTRM1240ST

120 Volts AC 60 Hz

Single phase, 3 wire grounded

Microwave 1650W

Toast 800W

1200 Watts full microwave power (IEC60705)

2450 MHz

2M214

0 ~ 90 min.

23”(W)x 12 1/2 ”(H)x 17 1/8 ”(D)

14 11/

16 ”(W)x 9

5

/

8 ”(H)x 15

5

/

8 ”(D)

15.9 kg (approx.)

17.3 kg (approx.)

Microwave Power for Variable Cooking

Power level

MAX ...................................... Full power throughout the cooking time

MED.-HIGH ............................ approx. 80% of Full power

MEDIUM ................................ approx. 60% of Full power

DEFROST .............................. approx. 40% of Full power

LOW/WARM ........................... approx. 20% of Full power

TOAST, COMBI

Owner's manual

Glass turntable

Roller rest

ITEM

MODEL

Power Requirement

Power Output

Microwave Frequency

Magnetron

Timer

Outside Dimensions

Cavity Dimensions

Net Weight

Shipping weight

Control Complement

Nameplate Location

Accessories

SPECIFICATIONS

Back Side

-4-

• 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.

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

-5-

INSTALLATIONS

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

TEMPORARY METHOD
(ADAPTER PLUGS NOT
PERMITTED IN CANADA)

ALIGN LARGE
PRONGS/SLOTS

ENSURE PROPER GROUND
AND FIRM CONNECTION
BEFORE USE

10cm

-6-

6. OVERALL CIRCUIT DIAGRAM
A. SCHEMATIC DIAGRAM

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-7-

B. MATRIX CIRCUIT FOR TOUCH KEY BOARD

-8-

7. OPERATING PROCEDURES
A. OVEN CONTROL PANEL

MICROWAVE CONTROL AREA

1. DISPLAY. The Display includes a clock and indicators that tell you time of day, cooking time settings, and cooking

functions selected.

2. STOP/CLEAR. Touch this pad to stop the oven or clear entries.

3. START. Touch this pad to start all entries (except the Auto Cook and Add Minute function which start automatically)

and to turn Child Lock on or off.

4. AUTO COOK. Touch this pad to select programming food items.

5. EZ-ON. Touch this pad to cook at 100% cook power for 1 minute to 99 minutes 59 seconds.

6. AUTO DEFROST. This pad is an accurate defrosting method for frozen meat, poultry and fish up to 6.0 lbs.

7. Q-DEFROST. This pad provides you with the quick defrosting method for 1.0 pound frozen foods.

8. CUSTOM SET. Touch this pad to change the oven's default settings for sound, clock, scroll speed and Lbs/Kg.

9. KITCHEN TIMER. Touch this pad to use your microwave oven as a kitchen timer.

10. COOK TIME. Touch this pad to set a cooking time.

11. POWER. Touch this pad to set a cooking power.

12. NUMBER PADS. Touch Number Pads to enter cooking time, power level, quantities, or weights.

13. SENSORTOUCH. This pad allows you to cook most of your favorite foods without having to select cooking times and

power levels.

TOASTER CONTROL AREA

1. Toast. Toast bread

2. Bagel. Toasts Bagels

3. Off/Clear. Touch this pad to stop the toaster or clear entries.

4. On. Touch this pad to start the toasting process.

5. Darkness Control. Adjust darkness control to desired setting before cooking foods.

(Default : 5, "1" is the lightest and "9" is the darkest)

6. Indicator Light. When operating toaster with door closed, this will be illuminated. If you open the door during
toasting, this will blink.

6

24 6 8 10

13 5 7 9 11 1 12 3

B. EASY USE TABLE

MICROWAVE OVEN

(1) KITCHEN TIMER

1. Touch STOP/CLEAR.

2. Touch KITCHEN TIMER.

3. Touch correct number for time.

4. Touch START.

(2) CHILD LOCK

To set:

1. Touch STOP/CLEAR.

2. Touch “START” more than 4 seconds.
To cancel:

1. Touch STOP/CLEAR.

2. Touch “START” more than 4 seconds.

(3) AUTO COOK

1. Touch STOP/CLEAR.

2. Touch AUTO COOK Category.

3. Touch START.
(Although you don’t touch start, it will start after
4 seconds automatically)

(4) EZ-ON

1. Touch STOP/CLEAR.

2. Touch EZ-ON

(5) AUTO DEFROST

1. Touch STOP/CLEAR.

2. Touch AUTO DEFROST.
Three different defrosting levels are provided.

(Touch 1 : Meat

Touch 2 : Poultry
Touch 3 : Fish)

3. Enter the weight of your food in decimal
increments from 0.1 to 6.0 pounds.

4. Touch START

5. At beeping, turn food over by following the
instructions in the manual.

6. After turning food over, touch START to resume
defrosting.

(6) TIMED COOKING

1. Touch STOP/CLEAR.

2. Touch COOK TIME.

3. Touch number for cooking time.

4. Touch POWER.

5. Touch number for cooking power level.

6. Touch START.

(7) MULTI-STAGE COOKING

1. Touch STOP/CLEAR.

2. Touch COOK TIME.

3. Touch number for cooking time.

4. Touch POWER.

5. Touch number for cooking power level.

6. Repeat steps 2-5 to set 2nd cooking stage.

7. Touch START.

TOASTER

(1) TOAST

1. Touch STOP/CLEAR.

2. Touch TOAST.

3. Touch Darkness Control (1~9 step)

4. Touch START.

(2) BAGEL

1. Touch STOP/CLEAR.

2. Touch BAGEL.

3. Touch Darkness Control (1~9 step)

4. Touch START.

(3) DARKNESS SETTINGS

-9-

Degree of darkness Select darkness level

Light 1~3

Medium 4~6

Dark 7~9

8. PROCEDURE FOR MEASURING MICROWAVE
ENERGY LEAKAGE

A. CAUTIONS

(1) Be sure to check a microwave emission prior to servicing

the oven if the oven is operative prior to servicing.

(2) The service personnel should inform the manufacturer,

importer, or assembler of any certified oven unit found to
have a microwave emission level in excess of
5mW/cm.sq. and 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.

(3) If the oven operates with the door open, the service

personnel should;

- Tell the user not to operate the oven

- Contact the manufacturer and CDRH (Center for
Devices and Radiological Health) immediately.
NOTE: Address on CDRH
Office of Compliance (HFZ-312)
Center for Devices and Radiological Health
1390 Piccard Drive
Rockville, Maryland 20850

(4) The service personnel should check all surface and vent

openings for microwave emission testing.

(5) Check for microwave energy leakage after every

servicing. The power density of the microwave radiation
leakage emitted by the microwave oven should not
exceed 1mW/cm.sq. And always start measuring of an
unknown field to assure safety for operating personnel
from radiation leakage.
NOTE: The standard is 5mW/cm.sq. while in the
customer’s home. 1mW/cm.sq. stated here is
manufacturer’s own voluntary standard for units in
customer’s home.

EQUIPMENT

• Electromagnetic energy leakage monitor (NARDA 8100B,
HOLADAY HI 1501)

• 600cc glass beaker

• Glass thermometer 1000C

B. MEASURING MICROWAVE ENERGY LEAKAGE

(1) Pour 275±15cc of 20±5 °C water in a beaker which is

graduated to 600 cc, and place the beaker in the center
of the oven.

(2) Set the energy leakage monitor to 2450 MHz and use it

following the manufacturer’s recommended test
procedure to assure correct result.

(3) When measuring the leakage, always use the 2 inch

(5cm) spacer supplied with the probe.
(4) Operate the oven at its maximum output.
(5) Measure the microwave radiation using and

electromagnetic radiation monitor by holding the probe

perpendicular to the surface being measured. (See

Figure 6)

Move probe along shaded area.

Probe scanning speed
less than 2.5 cm/sec.

C. MEASUREMENT WITH THE OUTER CASE REMOVED

(1) 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.

- Around the magnetron

- The waveguide

WARNING: AVOID CONTACTING ANY HIGH VOLTAGE

PARTS.

-10-

D. MEASUREMENT WITH A FULLY ASSEMBLED OVEN

(1) After all components, including the outer panels, are

fully assembled, measure for microwave energy
leakage around the door viewing window, the exhaust
opening and air inlet openings.

(2) Microwave energy leakage must not exceed the values

prescribed below.

NOTES:

Leakage with the outer panels removed - less than
5mW/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
1 mW/cm .sq.

E. NOTE WHEN MEASURING

(1) Do not exceed meter full scale deflection.
(2) The test probe must be removed no faster than 1

inch/sec (2.5cm/sec) along the shaded area, otherwise
a false reading may result.

(3) 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.

(4) 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.

F. RECORD KEEPING AND NOTIFICATION AFTER

MEASUREMENT

(1) 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.

(2) Should the microwave energy leakage not be more

than 1mW/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.

(3) At least once a year, have the electromagnetic energy

leakage monitor checked for calibration by its
manufacturer.

G. POWER OUTPUT MEASUREMENT

(1) Fill the test beaker with 59 °F(15 °C) ~ 75 °F(24 °C) 1 liter tap

water.

(2) Stir the water in the beaker with thermometer (°F or °C) and

measure temperature as T1.
(3) Place the beaker on the center of turntable.
(4) Set for one (1) minute and three (3) seconds and operate

the oven at high power.
NOTE: The additional three (3) seconds is to allow the

magnetron to begin generating power.

(5) When the heating is finished, stir the water again with

thermometer and measure the temperature of water as T2.
(6) Subtract T1 from T2, this will give you the temperature rise.
(7) The microwave power output is within specification, if the

temperature rise is as shown below:

(8) Power output will be influenced by line voltage of power

supply. Consequently, correct power output must be

measured within 120V AC ± 1 Volt while unit is operating.

SPECIAL TIP

• This oven used the button head screws.

• When you remove the screws, using the

tamper-resistant Torx driver have a

pin-in-head.

-11-

Line Voltage Degrees °F Degrees °C

120 V 17.1 ~ 22.5 9.5 ~ 12.5
108 V Min. 12.6 Min. 7.0

Temperature Rise

securing
screw

9. DISASSEMBLY INSTRUCTIONS
IMPORTANT NOTES:

UNIT MUST BE DISCONNECTED FROM ELECTRICAL
OUTLET WHEN MAKING REPAIRS, RE-PLACEMENTS,
ADJUSTMENTS AND CONTINUITY CHECKS. WAIT AT
LEAST ONE MINUTE, UNTIL THE HIGH VOLTAGE
CAPACITOR IN THE HIGH VOLTAGE POWER
SUPPLY HAS FULLY DISCHARGED. THE CAPACITOR
SHOULD BE DISCHARGED BY USING INSULATED
WIRE - I.E. TEST PROBE CONNECTED TO 10KOHM
RESISTOR IN SERIES TO GROUND. WHEN
RECONNECTING THE WIRE LEADS TO ANY PART,
MAKE SURE THE WIRING CONNECTIONS AND LEAD
COLORS ARE CORRECTLY MATCHED ACCORDING
TO THE OVERALL CIRCUIT DIAGRAM. (ESPECIALLY
SWITCHES ANDHIGH VOLTAGE CIRCUIT.)

A. REMOVING OUT CASE (Figures 7)

(1) Remove four screws from the rear section.
(2) Remove one screw from the side section.
(3) Push the outer case back about 1 inch (3cm).
(4) Lift the case from the set.

B. REMOVING COFFEE MAKER ASSEMBLY(Figure 8)

CAUTION: BE CAREFUL HOT SURFACE!

AFTER TOASTING, ENTIRE TOASTER’S
SURFACES ARE VERY HOT. BEFORE
SERVICING, COOL DOWN THE TOASTER

PARTS ENOUGH NOT TO GET BURNT.
(1) Open the door.
(2) Remove 2 screws, holding the toaster.
(3) Disconnect the 2 lead wires from connectors(CN2,CN3).
(4) Disconnect the wires at the secondary interlock switch

and wires at the toaster door switch.

(5) Disconnect the wires from the toaster thermostat and

wires at the Toaster Assembly.

(6) Lift up and pull out Toaster Assembly carefully from the

cavity.

Remove screw

Lift up and pull out toaster assembly

-12-

-13-

C. DOOR GROSS ASSEMBLY REMOVAL

(1) Open the door.
(2) Remove the choke cover cap 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.sq. (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.

D. MAGNETRON REMOVAL (Figure 10)

1) Disconnect the wire lead from the magnetron.

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

3) Remove the magnetron assembly 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.

E. REMOVING THE TURNTABLE MOTOR (Figure 11)

1) Remove the turntable and rotating ring.

2) Lay the unit down on its back.

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

4) Disconnect the leadwire from the turntable motor
terminals.

5) Remove the screw securing the turntable motor to the
oven cavity ASSEMBLY.

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

7) 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.

-14-

Magnetron

Waveguide

Magnetron
Gasket

Magnetron

Dome

Waveguide
Bracket

Turntable

Motor

Wire Leads

F. 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.

G. FAN MOTOR ASSEMBLY REMOVAL

1) Discharge the high voltage capacitor.

2) Disconnect the leadwire from fan motor and high voltage
capacitor.

3) Remove the two screws holding the the suction guide
ASSEMBLY to the oven cavity.

4) Remove the two screws holding the fan motor ASSEMBLY
to the suction guide ASSEMBLY.

H. HIGH VOLTAGE CAPACITOR AND DIODE REMOVAL

1) Discharge the high voltage capacitor.

2) Disconnect the leadwire from fan motor and high voltage
capacitor.

3) Remove the screw holding the suction guide ASSEMBLY to

the oven cavity.

4) Remove the screw holding the high voltage capacitor
bracket and remove the high voltage diode earth screw.

I. 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 this
adjustment. Make sure that the latch moves smoothly after
adjustment is completed and that the screws are tight.
Make sure the primary, monitor, and secondary switches
operate properly by following the continuity test
procedure.

-15-

-16-

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.

10. 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

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

Secondary
Switch

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

connected correctly.

COM

COM

NO

NC

NO

COM

-17-

11. TEST AND CHECKOUT PROCEDURES, AND TROUBLESHOOTING

A. TEST PROCEDURES

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.

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

HIGH VOLTAGE
TRANSFORMER
(Wire leads removed)

MAGNETRON
(Wire leads removed)

Approx.: 0.7 ~ 0.9 ohm
Approx.: 90 ~ 120 ohm
Less than: 1 ohm

Normal: Infinite
Normal: Infinite

Normal: Less than 1 ohm

Normal: Infinite

FILAMENT
WINDING

PRIMARY
TERMINAL

SECONDARY
WINDING

COMPONENTS TEST PROCEDURE RESULTS

1. Measure the resistance.
(Select the ohm scale on the meter)

• Primary winding

• Secondary winding

• Filament winding

2. Measure the resistance.
(Select the ohm scale on the meter)

• Primary winding to ground

• Filament winding to ground

1. Measure the resistance.
(Select the ohm scale on the meter)

• Filament terminal

2. Measure the resistance.
(Select the ohm scale on the meter)

• Filament to chassis

-18-

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

HIGH VOLTAGE
CAPACITOR

1. Check DC 9V battery before performing
tests.

2. Select the DCV scale on the meter.

3. Using the meter, battery, and jump wire,
connect the items as illustrated in figures.

• Terminal to terminal.

Normal: Approximately 9V

Normal: Approximately 0V or a

value displayed in mV
Will be seen.

1. Check DC 9V battery before performing
tests.

2. Select the DCV scale on the meter.

3. Using the meter, battery, and jump wire,
connect the items as illustrated in figures.

• Terminal to case.

COMPONENTS TEST PROCEDURE RESULTS

-19-

H.V.Diode (rectifer) STEP 1. Test the diode to see if it is shorted.

Procedure:

1. Select the Ω scale on the meter.

2. Place the meter leads across the diode as
pictured in Figure 14-a. The reading should be
“40MΩ,” “OL,” or a reading of infinity.

3. Reverse the meter leads. The reading should
again indicate a reading of infinity. If the diode
shows “infinity” in BOTH directions, it is NOT
shorted.

4. If the diode is not shorted, proceed to step 2.

STEP 2. Test the diode for forward biasing.

Procedure:

1. Select the DCV scale on the meter.

2. Using the meter, battery, and jumper wire,
connect the items as illustrated in Figure 14-b.
This has the positive side of the battery
connected to the cathode of the diode.

3. The diode should be forward biased therefore
a voltage reading of approximately 4.7 VDC to

6.4 VDC will be read depending on meter, battery
strength, etc. (Note: If the meter leads were
reversed, a negative voltage of the same amount
would be seen.)

STEP 3. Test the diode for reverse biasing.

Procedure:

1. Using the same scale on the meter, connect
the positive side of the battery to the anode of the
diode as illustrated in Figure 14-c.

2. The diode should be reverse biased therefore
a reading of 0 volt or a value displayed in mV will
be seen. (The display will be erratic changing
values rapidly in the mV scale.)

Normal:
Approximately
4 .7-6.4V

Normal:
Approximately 0V

COMPONENTS TEST PROCEDURE RESULTS

Figures 14-a Figures 14-b Figures 14-c

-20-

COMPONENTS TEST PROCEDURE RESULTS

RELAY 2
(Power Relay)

FAN MOTOR

TURNTABLE
MOTOR

1. Measure continuity.

2. Remove the lead wires and operate oven
at power level 1 through power level 10.

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.

1. Remove wire leads.

2. Measure resistance.

Normal:
A: Approximately
95~120 ohms.
B: Approximately
10~25 ohms.

Abnormal:
Infinite

Normal: Approx.2.5~3.5 Kohms
Abnormal: Infinite or several

ohm.

POWER

LEVEL

1
2
3
4
5
6
7
8
9

10

4 sec
6 sec

8 sec
10 sec
12 sec
14 sec
16 sec
18 sec
20 sec
22 sec

18 sec
16 sec
14 sec
12 sec
10 sec

8 sec
6 sec
4 sec
2 sec
0 sec

1. Remove wire leads.

2. Measure resistance.

B. CHECKOUT PROCEDURES

(1) CHECKOUT PROCEDURES FOR FUSE BLOWING

CAUTION: REPLACE BLOWN FUSE WITH 15 AMPERE FUSE.

NOTES:

- If the fuse is blown by an improper switch operation, replace the defective switches and the fuse at the same time.
After replacing the defective switches with new ones, make sure that they are correctly connected.

- Check for microwave energy leakage according to “1. ADJUSTMENT PROCEDURES” on page 3, when the
primary interlock, secondary interlock switches and/or the interlock monitor switches are adjusted or replaced.

-21-

PROBLEMS CAUSES

Fuse blows immediately after
the door is closed.

Improper operation of the primary interlock,
secondary interlock switches and/or the interlock
monitor switch.

Malfunction of the high voltage transformer; the high
voltage capacitor including the diode, the magnetron,
the blower motor or the circuit board.

Fuse blows immediately after
the door is opened.

Fuse blows when the door is closed and START key
is touched.

-22-

(2) CHECKOUT PROCEDURES FOR RELAY.

Microwave Oven

Toaster

- PROBLEM (A) ­FAN motor and oven lamp turn on without touching
START key when the door is closed.

Remove the mate connector of I/O
CON from the circuit board does
the unit still operate?

Replace the
circuit board

NO

NO

YES

GOOD

- PROBLEM (B) -

FAN motor and oven lamp turn on When the door is
closed and START key is touched.

Check the interlock switches

Replace the
micro switches.

Defective
RELAY or poor
connection of
relay

Replace
RELAY or correct
the connection.

YES

NO

NO

YES

GOOD

- PROBLEM (A) ­FAN motor and indicator light turn on without touching
START key when the door is closed.

Remove the mate connector of I/O
CON from the circuit board does
the unit still operate?

Replace the
circuit board

NO

NO

YES

GOOD

- PROBLEM (B) -

FAN motor and indicator light turn on When the door
is closed and START key is touched.

Check the interlock switches

Replace the
micro switches.

Defective
RELAY or poor
connection of
relay

Replace
RELAY or correct
the connection.

YES

NO

NO

YES

GOOD

(3) CHECKOUT PROCEDURES FOR CIRCUIT BOARD

The following symptoms indicate a defective circuit
board.
(1) The start function fails to operate but the high

voltage Systems, the interlock switches, the door

sensing and the relay check good.
(2) The unit with a normal relay continuously operates.
(3) The buzzer does not sound or continues to sound.

(4) Some segments of one or more digits do not light up, or

they continue to light up, or segments light when they

should not.
(6) Wrong figures appear.
(7) The figures of all digits flicker.
(8) Some of the indicators do no light up.
(9) The clock does not keep time properly.

-23-

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

SERVICED FOR ANY REASON.

-24-

CONDITION

Toaster and Microwave oven

does not work.

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

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 in oven.

Inconsistent intensity of
microwave by their
characteristics.

1. Use plastic wrap or lid.

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

Uneven microwave cooking.

Ceramic ware trimmed in
gold or silver powder is used.

Avoid using other electrical
appliances when you use this
unit.

Insert plug securely.

Use the this machine 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

C. TROUBLE SHOOTING

CAUTIONS

1. Check grounding and cool this unit before checking for trouble.

2. Be careful of the high voltage circuit.

3. Discharge the high voltage capacitor.

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 to ground while working on this panel to discharge any static charge built up in your body.
(Micom model only)

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 TOASTER AND

MICROWAVE OVEN. THIS CAN ELIMINATE AN UNNECESSARY SERVICE CALL.

-25-

CONDITION CHECK RESULT CAUSE REMEDY

1. No input can be
programmed.

Continuity.

No continuity.

Defective PCB
assembly.

Replace PCB
assembly.

Check the conn­ection between
membrane key
assembly and
PCB assembly.

Replace key
membrane
assembly and
check operation.

2. Some inputs
cannot be
programmed.

4. Random
programming
when touching
other pads.

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

3. Display shows a

number or figure
different from one
touched.

Everything works
as specified.

Still have trouble.

Loose
connection.

Connect them
tightly.

Defective key
membrane
assembly.

Replace key
membrane
assembly.

Defective PCB
assembly.

Replace PCB
assembly.

(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.

-26-

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.

CONDITION CHECK RESULT CAUSE REMEDY

(TROUBLE 2) Microwave oven does not operate at all, Display window does not display any figures,

and no input is accepted.

1. Fuse blows.

Continuity.

No continuity.

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).

Continuity.

No continuity.

Shorted contact at
the primary switch.

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

Check continuity
of primary
switch (with
door opened)

Normal.

Replace fuse

Fuse blows again

Defective high
voltage capacitor.

Replace high
voltage capacitor.

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

Defective high volt­age transformer.

Replace high volt­age transformer.

-27-

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

program times are set and START pad is touched.

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

1.Setting time
does not count
down when
touching START
pad.

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

No continuity.

Continuity.

Defective
secondary switch.

Replace
secondary switch.

Check continuity
of secondary
switch (with
door closed).

Check the con­nection between
CN1 connector
and PCB
assembly.

Continuity

No continuity

Abnormal

Abnormal

Normal

Defective fan motor.

Defective oven lamp.

Defective PCB
assembly.

Loose connection.

Output is low.

Lower than 90% of
rating voltage.

Normal.

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.

Measure the
output power.

Abnormal.

Abnormal.

Normal.

Defective PCB
assembly.

Defective
magnetron.

Replace PCB
assembly.

Replace
magnetron.

Replace PCB
assembly.

Connect them
tightly.

Replace fan motor.

Replace

oven lamp.

Check fan motor.

Check oven lamp.

CONDITION CHECK RESULT CAUSE REMEDY

CONDITION CHECK RESULT CAUSE REMEDY

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

Minimum 8.5oC temperature rise is normal condition.

-28-

CONDITION CHECK RESULT CAUSE REMEDY

(TROUBLE 5) No microwave oscillation even though oven lamp and fan motor run.

(Display operates properly)

No microwave
oscillation.

No continuity.

Continuity.

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

Defective PCB
assembly

Defective high
voltage
transformer.

Replace PCB
assembly

Output is full power
when you set lower
power level.

Abnormal.

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

Defective PCB
assembly

Replace PCB
assembly

Replace high
voltage
transformer.

Defective high
voltage capacitor.

Replace high
voltage capacitor.

Abnormal

Normal

Check high vol­tage transformer

Abnormal

Normal

Check high vol­tage capacitor.

Defective high
voltage diode.

Replace high
voltage diode.

Abnormal

Normal

Check high vol­tage diode.

Defective
magnetron.

Replace
magnetron.

Abnormal

Check
magnetron.

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.

-29-

(TROUBLE 6) When toaster operates, strange code can be seen on the display and stop with beep sound.

1. “F-1” code.

No continuity.

Continuity.

Defective
thermistor

Replace thermistor

Check continuity
of thermistor.

Check the
continuity of
heater.

Check the
connection
between CN3
connector and
PCB assembly.

Continuity.

No continuity.

Continuity.

No continuity.

Defective heater

Defective PCB
assembly.

2. “F-2” code.

Attached

Seperated

2 wire leads are
shorted contact

Internal
temperature is
over 220 deg c

Apart 2 wire leads
as far as possible.

Check the CN3
connector
whether 2 wire
leads are
attached.

3. “HOT” code.

Allow the toaster to
cool down.
(Automatically fan
will blow for
3 minutes to cool
this unit)

Defective PCB
assembly.

Replace PCB
assembly.

Replace toaster
Assembly.

Replace PCB
Assembly.

Loose connection

Connect them
tightly.

CONDITION CHECK RESULT CAUSE REMEDY

-30-

EXPLODED VIEW

INTRODUCTION

-31-

DOOR PARTS

14890A

13213A

13536A

13552A

15006A

13581A

14026A

14970A

WTP004

268712

13720D

13650A

13551A

For model
LTRM1240ST

23506A

For model
LTRM1240SB
LTRM1240SW

WTT028

-32-

OVEN CAVITY PARTS

33112U

WTT010

WTT020

33390G

35889A

WTP013

36549S

33052A

WSZ185

LTRM1240SB

LTRM1240ST

For model

For model

LTRM1240SW

-33-

LATCH BOARD PARTS

WSZ085

56912B

55262A

466003

466001

466001

43500A

44510A

-34-

OVEN INTERIOR PARTS

568771

56930V

WTT028

56324A

WSZ002

WTT028

56851D

WSZ002

54810C

50CZZH

WSZ002

55900A

54974S

56549F

568772

WTT037

WSZ002

56411A

WTT024

34930W

35012A

55006F

50FZZA

WSZ

002

268711

-35-

BASE PLATE PARTS

63302A

WTT021

65006A

647781

WTT028

WTT021

WSZ002

56170D

63303A

-36-

SENSOR PARTS

WTP004

56501A

WTT021

54974T

-37-

COFFEE MAKER PARTS

75993M

73550L

768711

74970A

73650A

73551B

73720D

73213A

73552A

73572A

73740A

73551C

73551A

766001

74510L

76322A

76930V

For LTRM1240ST

For LTRM1240ST