LG MH-685HD Service Manual ▷ View online
5-14
CONDITION
No input can be
programmed.
programmed.
Some inputs can not be
programmed.
programmed.
Display fixes some figure and
can not accept any input.
can not accept any input.
Set time does not count
down when touched START.
down when touched START.
H.M.MOTOR not operating.
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.
Defective tact switch key of
P.C.B.
P.C.B.
Loose connection.
Connect them tightly.
Defective secondary switch
or out of adjustment
or out of adjustment
Defective tact switch key of
P.C.B.
P.C.B.
Test procedure tact switch
key of P.C.B.
key of P.C.B.
Test procedure secondary
switch.
switch.
Test procedure tact switch
key of P.C.B.
key of P.C.B.
CAUSE
TEST PROCEDURE OR
CORRECTION
Incorrect touch key.
Touch key again after
closing.
closing.
Loose connection.
• Loose
Gear of H.M.MOTOR
• Loose PCB connector
No. CN6 and H.M.M S/W1,
S/W2
S/W2
Test tact switch key of
P.C.B.
P.C.B.
• To Adjust Gear of
H.M.MOTOR
• To Fasten PCB CN6.
• To check H.M.MOTOR
• To check H.M.MOTOR
S/W1, S/W2
(TROUBLE 2) Oven does not at all even thought MOTOR and P.C.B program.
5-15
CONDITION
Oven does not go into a
cook cycle when START key
is touched.
cook cycle when START key
is touched.
Primary and secondary
interlock switches defective
or out of adjustment.
interlock switches defective
or out of adjustment.
Defective relay 1 of P.C.B.
Test procedure relay 1 of
P.C.B.
P.C.B.
Test procedure primary and
secondary switches.
secondary switches.
CAUSE
TEST PROCEDURE OR
CORRECTION
Defective tact switch key of
P.C.B.
P.C.B.
Test procedure tact switch
key of P.C.B.
key of P.C.B.
Open or loose wiring to
above components.
above components.
Check and repair wiring.
Ouput power is too low.
Defective fan motor.
Low AC input voltage.
Use the microwave oven at
adequate line voltage.
adequate line voltage.
Test procedure fan motor.
Food temperature is too low.
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.
Defective relay 5 of P.C.B.
Test procedure relay 5 of
P.C.B.
P.C.B.
Uneven cooking.
Inconsistent intensity of
microwave by their
characteristics.
microwave by their
characteristics.
Food does not turn during
cook cycle.
cook cycle.
Food or cookware extending
oven edges of turntable
prevents turning rearrange food.
oven edges of turntable
prevents turning rearrange food.
1. Wrap the thinner part with
aluminum foil.
2. Use plastic wrap or with a lid.
3. Stir once or twice while cooking
3. Stir once or twice while cooking
soup, cocoa or milk etc.
Turntable motor does not
operate.
operate.
Refer to preceding turntable
motor problem.
motor problem.
Output is too high when you
set lower power level.
set lower power level.
Defective relay 5 of P.C.B.
High AC input voltage.
Use the microwave oven at
adequate line voltage.
adequate line voltage.
Test procedure relay 5 of
P.C.B.
P.C.B.
(TROUBLE 3) Oven does not operating microwave cooking
5-16
CONDITION
No microwave oscillation.
Defective relay 5 of P.C.B.
• Defective high voltage
transformer.
• Defective of thermal Cut-
out high voltage
transformer.
transformer.
Test procedure high voltage
transformer and thermal
Cut-out of high voltage
transformer.
transformer and thermal
Cut-out of high voltage
transformer.
Test procedure relay 5 of
P.C.B.
P.C.B.
CAUSE
TEST PROCEDURE OR
CORRECTION
Defective high voltage
capacitor.
capacitor.
Test procedure high voltage
capacitor.
capacitor.
Defective high voltage
diode.
diode.
Defective magnetron.
Test procedure magnetron.
Test procedure high voltage
diode.
diode.
Low AC input voltage.
Open or loose wiring to
above components.
above components.
Check and repair wiring.
Use the microwave oven at
adequate line voltage.
adequate line voltage.
Spark occurring.
Using metallic ware and
allowing it to touch the
oven wall.
allowing it to touch the
oven wall.
Ceramic ware trimmed in
gold or silver powder is used.
gold or silver powder is used.
Do not use any type of cook
ware with metallic trimming.
ware with metallic trimming.
Do not use metallic ware for
cooking except where noted
in the cookbook.
cooking except where noted
in the cookbook.
Grill rack or roti-bar is using
in no load condition.
in no load condition.
Do not use the oven at
microwave and combination
mode with the grill rack or
roti-bar placed in the cavity
when the oven is empty.
microwave and combination
mode with the grill rack or
roti-bar placed in the cavity
when the oven is empty.
(TROUBLE 3) Oven does not operating microwave cooking
5-17
CONDITION
Grill indicator lights
but oven does not go into
cook cycle when START key
is touched.
but oven does not go into
cook cycle when START key
is touched.
Temperature in the oven
cavity is lower or higher then
preset.
cavity is lower or higher then
preset.
Grill Heater not operating.
Defective relay 4 of P.C.B.
Open or loose wire
connection to the above
components.
connection to the above
components.
Check and repair wiring.
Test procedure relay 4 of
P.C.B.
P.C.B.
CAUSE
TEST PROCEDURE OR
CORRECTION
Open or loose wire
connection to P.C.B.
connection to P.C.B.
Two lead wires (Live,
neutral parts) feeding the
Noise filter are
interchanged.
At this time, microwave
mode normally operates.
neutral parts) feeding the
Noise filter are
interchanged.
At this time, microwave
mode normally operates.
Interchange live part wire
with neutral part wire
correctly.
with neutral part wire
correctly.
Check and repair wiring.
Defective relay 2 of P.C.B.
Defective grill heater
element.
element.
Defective moving heater
motor.
motor.
• Defective Gear of moving
heater motor and too loose
of PCB connector CN6.
of PCB connector CN6.
Test procedure grill heater.
Test procedure moving
heater motor.
heater motor.
Test procedure Moving
heater Motor and PCB CN6
connector.
heater Motor and PCB CN6
connector.
Test procedure relay 2 of
P.C.B.
P.C.B.
(TROUBLE 5) Oven does not operating Grill cooking
NOTE :• MAKE SURE THE WIRE LEADS CORRECT POSITION.
• WHEN REMOVING THE WIRE LEADS FROM THE PARTS, BE SURE TO GRASP THE CONNECTOR,
AND NOT THE WIRES.
• WHEN REMOVING THE MAGNETRON, BE SURE TO INSTALL THE MAGNETRON GASKET IN THE
CORRECT POSITION AND GOOD CONDITION.
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