DOWNLOAD LG MS-1904H Service Manual ↓ Size: 1.21 MB | Pages: 38 in PDF or view online for FREE

MICROWAVE OVEN

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

5-9

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

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: 

Abnormal: 

∞

or several 

Ω

Normal: Approx. 100~200 

§

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.

Relay 1

Relay 2

Power
Transformer

A

B

C

A ~ B           A ~ C

30 ~ 50

Ω

300~500

Ω

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

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)

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.