LG MS-255T Service Manual ▷ View online
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
switches, and
RELAY(RY2) of
P.C.B Assembly.
primary, monitor
switches, and
RELAY(RY2) of
P.C.B Assembly.
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
switches, and
RELAY(RY2) of
P.C.B Assembly.
primary, monitor
switches, and
RELAY(RY2) of
P.C.B Assembly.
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
2. Fuse does not
blow.
No continuity.
Continuity.
No continuity.
Defective power
supply cord.
supply cord.
Replace power
supply cord.
supply cord.
Defective
thermostat.
thermostat.
Replace
thermostat.
thermostat.
Check continuity
of thermostat.
of thermostat.
Check continuity
of power supply
cord.
of power supply
cord.
(TROUBLE 2) Oven does not operate at all; Display window does not display any figures,
and no input is accepted.
NOTE : All these switches must be replaced at the same time. Refer to page 5-6, 5-7
5-14
CONDITION
CHECK
RESULT
CAUSE
REMEDY
1. Setting time
does not count
down when
touching START
pad.
down when
touching START
pad.
2. Fan motor or
oven lamp do
not turn on.
not turn on.
No continuity.
Continuity.
Continuity
Defective PCB
assembly.
assembly.
Loose connection.
Replace PCB
assembly.
assembly.
Connect them
tightly.
tightly.
No continuity
Abnormal
Check fan motor.
Defective fan motor.
Replace fan motor.
Abnormal
Normal
Check oven lamp.
Defective oven lamp.
Replace oven lamp.
Defective
secondary switch.
secondary switch.
Replace
secondary switch.
secondary switch.
Check continuity
of secondary
switch (with
door closed).
of secondary
switch (with
door closed).
Check the con-
nection between
CN1 connector
and PCB
assembly.
nection between
CN1 connector
and PCB
assembly.
(TROUBLE 3) Display shows all figures set, but oven does not start cooking while desired
program times are set and START pad is touched.
(TROUBLE 4) Oven seems to be operating but little heat is produced in oven load.
NOTE : Simple test of power output-conducted by heating one liter water for one min. if available.
Minimum 8.5°C temperature rise is normal condition.
CONDITION
CHECK
RESULT
CAUSE
REMEDY
Output is low
Lower than 90% of
rating voltage.
rating voltage.
Normal
Abnormal
Defective PCB
assembly.
assembly.
Replace PCB
assembly.
assembly.
Normal
Abnormal
Measure the
output power.
output power.
Defective
magnetron.
magnetron.
Replace
magnetron.
magnetron.
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.
power source
voltage.
Disconnect the
wire leads from
relay 2 and
check on and off
time with
multitester.
wire leads from
relay 2 and
check on and off
time with
multitester.
5-15
CONDITION
CHECK
RESULT
CAUSE
REMEDY
No microwave
oscillation.
oscillation.
No continuity.
Continuity.
Abnormal
Defective high
voltage
transformer.
voltage
transformer.
Replace high
voltage
transformer.
voltage
transformer.
Normal
Defective PCB
assembly.
assembly.
Replace PCB
assembly.
assembly.
Disconnect the
wire leads from
relay 2 and
check continuity
of relay 2.
(Operate the unit)
wire leads from
relay 2 and
check continuity
of relay 2.
(Operate the unit)
Check high vol-
tage transformer.
tage transformer.
Abnormal
Defective circuit
protector.
protector.
Replace circuit
protector.
protector.
Normal
Check circuit
protector.
protector.
Abnormal
Defective high
voltage capacitor.
voltage capacitor.
Replace high
voltage capacitor.
voltage capacitor.
Normal
Check high vol-
tage capacitor.
tage capacitor.
Abnormal
Defective high
voltage diode.
voltage diode.
Replace high
voltage diode.
voltage diode.
Normal
Check high vol-
tage diode.
tage diode.
Abnormal
Defective
magnetron.
magnetron.
Replace
magnetron.
magnetron.
Check
magnetron.
magnetron.
(TROUBLE 5) No microwave oscillation even though oven lamp and fan motor run.
(Display operates properly)
5-16
Output is full power
when you set lower
power level.
when you set lower
power level.
Abnormal.
Defective PCB
assembly.
assembly.
Replace PCB
assembly.
assembly.
Disconnect the
wire leads from
relay 2 and check
continuity relay 2.
(Operate the unit)
wire leads from
relay 2 and check
continuity relay 2.
(Operate the unit)
NOTE : • Make sure the wire leads correct position.
• When Removing the wire leads from the parts, be sure to grasp the connector, not the wires.
• When removing the magnetron, be sure to install the magnetron gasket in the correct position
• When removing the magnetron, be sure to install the magnetron gasket in the correct position
and in good condition.
CONDITION
CHECK
RESULT
CAUSE
REMEDY
(TROUBLE 5) No microwave oscillation even though oven lamp and fan motor run.
(Display operates properly)
Click on the first or last page to see other MS-255T service manuals if exist.