LG MS-255T Service Manual ▷ View online
NECESSARY TOOLS
Tools normally used for TV servicing are sufficient.
Standard tools are listed below.
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
• 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.
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
oven unit found to have a microwave emission
level in excess of 5 mW/cm
2
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.
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.
- 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/cm
emitted by the microwave oven should not exceed
5 mW/cm
2
. Always start measuring of an unknown field
to assure safety for operating personnel from radiation
leakage.
leakage.
NECESSARY MEASURING INSTRUMENTS
• TESTER(VOLTS-DC, AC., Ohmmeter)
• Microwave survey meter
• Microwave survey meter
- Holaday HI-1500
HI-1501
- Narda 8100
8200
• Inch scale
• 600 cc non conductive material beaker (glass or
• 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
outside diameter: approx. 190mm
height: approx. 90mm
• Glass thermometer: 100°C or 212°F (1 deg scale)
MEASURING MICROWAVE ENERGY
LEAKAGE
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.
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.
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
• Measure the microwave radiation using and
electromagnetic radiation monitor by holding the
probe perpendicular to the surface being measured
probe perpendicular to the surface being measured
Move probe along shaded area
Probe scanning speed
Less than 2.5 cm/sec
( 1in/sec)
Less than 2.5 cm/sec
( 1in/sec)
5-1
SERVICE INFORMATION
TOOLS AND MEASURING INSTRUMENTS
MICROWAVE LEAKAGE TEST
COMPONENTS
TEST PROCEDURE
RESULTS
5-10
RELAY 2
FAN MOTOR
(Wire leads removed)
(Wire leads removed)
TURNTABLE
MOTOR
(Wire leads removed)
MOTOR
(Wire leads removed)
Check for continuity of relay 2 with an
ohm-meter.
(Remove wire leads from relay 2 and
operate the unit.)
ohm-meter.
(Remove wire leads from relay 2 and
operate the unit.)
Measure the resistance.
(Ohm-meter scale: R x 100)
(Ohm-meter scale: R x 100)
Measure the resistance.
(Ohm-meter scale: R x 1000)
(Ohm-meter scale: R x 1000)
POWER
LEVEL
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: 350~450 Ω
Abnormal: ∞ or several Ω
Normal: Approx. 16 KΩ
Abnormal: ∞ or several Ω
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
• WHEN REMOVING THE WIRE LEADS FROM THE PARTS, BE SURE TO GRASP THE
CONNECTOR, NOT THE WIRES.
Relay 1
Relay 2
Power
Transformer
Transformer
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.
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
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.
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)
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)
plug outlet and using
them at the same time
(blown fuse or breaker)
Microwave oven plug is not
inserted tightly.
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.
allowing it to touch the oven
wall.
Sparks occur.
Inconsistent intensity of
microwave by their
characteristics.
microwave by their
characteristics.
1. Wrap the thinner part with
aluminum foil
2. Use plastic wrap or lid.
3. Stir once or twice while
3. Stir once or twice while
cooking soup, cocoa or
milk, etc.
milk, etc.
Uneven cooking.
Ceramic ware trimmed in
gold or silver power is used.
gold or silver power is used.
Avoid using other electrical
appliances when you use the
microwave oven.
appliances when you use the
microwave oven.
Insert microwave oven plug
securely.
securely.
Use the microwave oven at
adequate line voltage.
adequate line voltage.
This may not be a defect.
It is possible that the food
should be cooked for a
longer time period.
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.
cooking except where noted
in the cooking guide.
Do not use any type of
cookware with metallic
trimming.
cookware with metallic
trimming.
CAUSE
REMEDY
1. Incomplete segments.
• Segment missing.
• Partial segment missing.
• Digit flickering (NOTE:Slight flickering is normal.)
• 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
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.
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.
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.
assembly.
Loose
connection.
connection.
Replace PCB
assembly.
assembly.
Connect them
tightly.
tightly.
Check the conn-
ection between
membrane key
assembly and
PCB assembly.
ection between
membrane key
assembly and
PCB assembly.
2. Some inputs
cannot be
programmed.
programmed.
3. Display shows a
number or figure
different from one
touched.
different from one
touched.
4. Random
programming
when touching
other pads.
when touching
other pads.
5. Display is fixed
at some figure
and can not
accept any
input.
and can not
accept any
input.
Everything works
as specified.
as specified.
Still have trouble.
Defective key
membrane
assembly.
membrane
assembly.
Defective PCB
assembly.
assembly.
Replace key
membrane
assembly.
membrane
assembly.
Replace PCB
assembly.
assembly.
Replace key
membrane
assembly and
check operation.
membrane
assembly and
check operation.
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