LG MB-393T Service Manual ▷ View online
5-12
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.
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 circuitry on the digital programmer circuit 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.
CONDITION
Microwave oven
does not work.
Inserting many plug into one
plug outlet and using
them at the same time
(causes overloading).
plug outlet and using
them at the same time
(causes overloading).
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 occurring.
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 powder is used.
gold or silver powder 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
5-13
CONDITION
CHECK
RESULT
CAUSE
REMEDY
1. Fuse blows.
Continuity.
No continuity.
Continuity.
Shorted contact at
the primary switch.
the primary switch.
Replace fuse,
primary, monitor
and secondary
switches.
primary, monitor
and secondary
switches.
No continuity.
Normal.
Defective high
voltage capacitor.
voltage capacitor.
Replace high
voltage capacitor.
voltage capacitor.
Fuse blows again
Defective high volt-
age transformer.
age transformer.
Replace high volt-
age transformer.
age transformer.
Malfunction of the
monitor switch.
monitor switch.
Replace fuse,
primary, monitor
and secondary
switches.
primary, monitor
and secondary
switches.
Check continuity
of monitor
switch (with
door closed).
of monitor
switch (with
door closed).
Check continuity
of primary
switch (with
door opened).
of primary
switch (with
door opened).
Disconnect one
side of the wire
lead connected
from transformer
to the high
voltage
capacitor and
operate the unit.
side of the wire
lead connected
from transformer
to the high
voltage
capacitor and
operate the unit.
Replace fuse
1. Oven does not
operate.
No continuity.
No continuity.
Adjust or replace.
Malfunction of the
primary switch.
primary switch.
Malfunction of the
secondary switch.
secondary switch.
Adjust or replace.
Check the
continuity of the
primary switch
with door
closed.
continuity of the
primary switch
with door
closed.
Check the
continuity of the
secondary
switch with
secondary
switch pushed.
continuity of the
secondary
switch with
secondary
switch pushed.
(TROUBLE 1) Oven lamp does not turn on when the timer knob is pushed with door closed.
(TROUBLE 2) Oven does not start even though the timer is set.
NOTE : All these switches must be replaced at the same time.
This fuse is a special type of fuse which is kept as spare part by the importer.
CONDITION
CHECK
RESULT
CAUSE
REMEDY
5-14
(TROUBLE 3) Output power is low.
CONDITION
CHECK
RESULT
CAUSE
REMEDY
Output is low
Lower than 207V.
Normal
Less than 8.5
o
C.
Measure the
magnetron’s
output(See test
procedure).
magnetron’s
output(See test
procedure).
Faulty magnetron.
Replace.
Decrease in power
source voltage
with load.
source voltage
with load.
Suggest customer
contact local
electric power
utility co. or
qualified
electrician.
contact local
electric power
utility co. or
qualified
electrician.
Check the
power source
voltage
oscillating.
power source
voltage
oscillating.
No continuity.
No continuity.
replace.
Malfunction of the
timer switch.
timer switch.
Faulty thermostat.
replace.
Check the
continuity of the
timer switch
contacts.
continuity of the
timer switch
contacts.
Check the
continuity of the
thermostat.
continuity of the
thermostat.
CONDITION
CHECK
RESULT
CAUSE
REMEDY
(TROUBLE 4) Grill.
CONDITION
CHECK
RESULT
CAUSE
REMEDY
1. Heater is not
operating.
Abnormal.
Normal.
Normal.
Heater.
Thermostat
(Grill)
(Grill)
Abnormal.
Malfunction the
thermostat.
thermostat.
Malfunction the
heater.
heater.
Replace.
Wire connection.
No continuity.
Open or loosen.
Replace.
Replace.
5-15
CONDITION
CHECK
RESULT
CAUSE
REMEDY
No microwave
oscillation.
oscillation.
No continuity.
Continuity.
Abnormal or burn
out.
out.
Defective monitor
resistor.
resistor.
Replace.
Malfunction of the
power control
switch.
power control
switch.
Replace the power
control switch.
control switch.
Check the
power control
switch(cooking
state).
power control
switch(cooking
state).
Check the
monitor resistor.
monitor resistor.
Abnormal
Defective AC
relay.
relay.
Replace.
Normal
Check the AC
relay.
relay.
Abnormal
Open the
secondary winding
of the high voltage
transformer of
faulty insulation of
filament winding.
secondary winding
of the high voltage
transformer of
faulty insulation of
filament winding.
Replace .
Check H.V.
transformer.
transformer.
Abnormal
Shorted H.V. diode
Replace .
Check H.V.
diode.
diode.
Abnormal
Faulty capacitor.
Replace .
Check H.V.
capacitor.
capacitor.
Abnormal
Faulty magnetron.
Replace .
Magnetron
(TROUBLE 5) Oven does not cook at all even though turntable rotates.
Click on the first or last page to see other MB-393T service manuals if exist.