LG MS-285SD Service Manual ▷ View online
5-12
COMPONENTS
TEST PROCEDURE
RESULTS
CN2
1
3
5
Relay 2
1
2
3
4
5
6
7
8
9
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Main
P.C.B
Key PCB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Cooking Start
OFF
Cooking Start
OFF
Check continuity between
switch terminals, by pressing an
appropriate pad on key board.
The contacts assignment of the
respective pads on the key
board is as shown left figures.
switch terminals, by pressing an
appropriate pad on key board.
The contacts assignment of the
respective pads on the key
board is as shown left figures.
RELAY 1 OF P.C.B
(Disconnect the 5 pin
connector from P.C.B)
See Schematic Dagram on
page 4-4)
RY1 : Turn Table,
(Disconnect the 5 pin
connector from P.C.B)
See Schematic Dagram on
page 4-4)
RY1 : Turn Table,
Fan Motor,
Oven Lamp
Oven Lamp
RELAY 2 OF P.C.B
(Wire leads removed.)
RY2 : Microwave
(Wire leads removed.)
RY2 : Microwave
CONTROL PANEL PCB
NOTE : A MICROWAVE ENERGY LEAKAGE TEST MUST ALWAYS BE PERFORMED WHEN THE UNIT IS
SERVICED FOR ANY REASON.
MAKE SURE THE WIRE LEADS ARE CORRECT POSITION.
WHEN REMOVING THE WIRE LEAD FROM THE PARTS, BE SURE TO GRASP THE
CONNECTOR, NOT THE WIRES.
MAKE SURE THE WIRE LEADS ARE CORRECT POSITION.
WHEN REMOVING THE WIRE LEAD FROM THE PARTS, BE SURE TO GRASP THE
CONNECTOR, NOT THE WIRES.
Trouble Shooting Guide
5-13
CAUTIONS
1. Check grounding before checking for other trouble.
2. Be careful of the high voltage circuit.
3. When checking the continuity of the switches or transformer, disconnect one lead wire from these parts and
then check continuity without turning the power source on.
4. Do not touch any part of the circuitry on the control circuit board, since static electric discharge may damage
this control circuit.
Always touch yourself to ground while working on this circuit to discharge any static charge built up in your
body.
Always touch yourself to ground while working on this circuit to discharge any static charge built up in your
body.
5. First operate the microwave oven following the correct operating.
6. If the oven become inoperative because of a fuse, check the primary, the secondary and the monitor switches
before replacing the fuse.
(TROUBLE 1) Oven does not operate all.
CONDITION
CAUSE
OFF CONDITION
The fuse blows when power
cord is plugged into wall
receptacle.
cord is plugged into wall
receptacle.
"0" does not appear in
displasy window when
power cord is first plugged
into wall outlet.
displasy window when
power cord is first plugged
into wall outlet.
Display does not operate
properly when CLOCK is
touched.
properly when CLOCK is
touched.
Shorted lead wire assy or
wire harness.
wire harness.
Defective monitor switch or
out of adjustment.
out of adjustment.
Microwave oven plug is not
inserted tightly.
inserted tightly.
No power at outlet.
Check home fuse.
Blown fuse.
Test procedure fuse.
Open wire in power cord,
wiring harness, or wiring
between control panel
assembly units.
wiring harness, or wiring
between control panel
assembly units.
Defective tact switch key of
P.C.B.
P.C.B.
Replace or repair wiring.
Test procedure tact switch
key.
key.
Replace lead wire or check
and repair wire hardness.
and repair wire hardness.
Test procedure switches.
Insert microwave oven plug
securely.
securely.
TEST PROCEDURE OR
CORRECTION
5-14
CONDITION
CAUSE
No input can be
programmed.
programmed.
Some inputs can not be
programmed.
programmed.
Display shows a number or
figure different from one
touched.
figure different from one
touched.
Random programming when
pressing other than touch
keys.
pressing other than touch
keys.
Display fixes some figure
and can not accept any
input.
and can not accept any
input.
Set time does not count
down when touched START.
down when touched START.
Defective tact switch key of
P.C.B.
P.C.B.
Loose connection.
Incorrect touch key.
Defective secondary switch
or out of adjustment
or out of adjustment
Defective tact switch key of
P.C.B.
P.C.B.
Loose connection.
Test procedure tact switch
key of P.C.B.
key of P.C.B.
Connect them tightly.
Touch key again after
closing.
closing.
Test procedure
secondary switch.
secondary switch.
Test procedure tact switch
key of P.C.B.
key of P.C.B.
Test tact switch key of
P.C.B.
P.C.B.
TEST PROCEDURE OR
CORRECTION
(TROUBLE 2) Oven does not at all even thought P. C. B program.
5-15
CONDITION
CAUSE
Oven does not go into a
cook cycle when START key
is touched.
cook cycle when START key
is touched.
Ouput power is too low.
Output is too high when you
set lower power level.
set lower power level.
Uneven cooking.
Primary and secondary
interlock switches defective
or out of adjustment.
interlock switches defective
or out of adjustment.
Defective relay 1, 2 of
P.C.B.
P.C.B.
Defective tact switch key of
P.C.B.
P.C.B.
Open or loose wiring to
above components.
above components.
Defective fan motor.
Low AC input voltage.
Food temperature is too low.
Defective relay 2 of P.C.B.
Defective relay 2 of P.C.B.
High AC input voltage.
Inconsistent intensity of
microwave by their
characteristics.
microwave by their
characteristics.
Food does not turn during
cook cycle.
cook cycle.
Turntable motor does not
operate.
operate.
Test procedure primary and
secondary switches.
secondary switches.
Test procedure relay 1, 2 of
P.C.B.
P.C.B.
Test procedure tact switch
key of P.C.B.
key of P.C.B.
Check and repair wiring.
Test procedure fan motor.
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 period.
It is possible that the food
should be cooked for a
longer period.
Test procedure relay 2 of
P.C.B.
P.C.B.
Test procedure relay 2 of
P.C.B.
P.C.B.
Use the microwave oven at
adequate line voltage.
adequate line voltage.
1. Wrap the thinner part with
aluminum foil.
2. Use plastic wrap or with a lid.
3. Stir once or twice while cook-
3. Stir once or twice while cook-
ing soup, cocoa or milk etc.
Food or cookware extending
oven edges of turntable prevents
turning rearrange food.
oven edges of turntable prevents
turning rearrange food.
Refer to preceding turntable
motor problem.
motor problem.
TEST PROCEDURE OR
CORRECTION
(TROUBLE 3) Oven does not operating microwave cooking
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