LG MB-395T Service Manual ▷ View online
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 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.
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.
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.
5-13
(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.
5-14
CONDITION
CHECK
RESULT
CAUSE
REMEDY
1. Fuse blows.
Continuity.
No continuity.
Continuity.
Shorted contact at
the primary switch.
the primary switch.
Replace primary
and monitor
switches.
and monitor
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 primary
and monitor
switches.
and monitor
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
(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
2. Fuse does not
blow.
No continuity.
No continuity.
Replace power
supply cord.
supply cord.
Defective mag-
netron thermostat.
netron thermostat.
Defective power
supply cord.
supply cord.
Replace mag-
netron thermostat.
netron thermostat.
Check continuity
of magnetron
thermostat.
of magnetron
thermostat.
Check continuity
of power supply
cord.
of power supply
cord.
Continuity.
5-15
(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 operation but little heat is produced in oven load.
CONDITION
CHECK
RESULT
CAUSE
REMEDY
1.Setting time does
not count down
when touching
START pad.
when touching
START pad.
2. Fan motor or
oven lamp
do not turn
on.
do not turn
on.
No continuity.
continuity.
No continuity.
Continuity.
Check the con-
nection between
connector and
P.C.B assembly.
nection between
connector and
P.C.B assembly.
Defective
secondary switch.
secondary switch.
Replace
secondary switch.
secondary switch.
Defective P.C.B
assembly.
assembly.
Replace P.C.B
assembly.
assembly.
Check continuity
of secondary
switch (with
door closed).
of secondary
switch (with
door closed).
Check fan motor.
Check oven lamp.
Abnormal.
Abnormal.
Normal.
Defective fan
motor.
motor.
Defective fan
motor.
motor.
Replace fan
motor.
motor.
Replace fan
motor.
motor.
Loose connection.
Connection then
tightly.
tightly.
CONDITION
CHECK
RESULT
CAUSE
REMEDY
Output is low.
Lower than 90% of
rating voltage.
rating voltage.
Normal.
Abnormal.
Abnormal.
Measure the
output power.
output power.
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.
Defective P.C.B
assembly.
assembly.
Replace P.C.B
assembly.
assembly.
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.
Defective
magnetron.
magnetron.
Replace
magnetron.
magnetron.
NOTE: Simple test of power output-conducted by heating one liter water for one min. if available.
5-16
CONDITION
CHECK
RESULT
CAUSE
REMEDY
No microwave
oscillation.
oscillation.
No continuity.
Continuity.
Defective P.C.B
assembly
assembly
Replace P.C.B
assembly
assembly
Disconnect the
wire leads from
relay 2 and
check continuity
of relay2.
(Operate the
unit)
wire leads from
relay 2 and
check continuity
of relay2.
(Operate the
unit)
Abnormal
normal
Defective high
voltage
transformer.
voltage
transformer.
Replace high
voltage
transformer .
voltage
transformer .
Check H.V.
transformer.
transformer.
normal
normal
Abnormal
Defective high
voltage Diode.
voltage Diode.
Replace high
voltage Diode.
voltage Diode.
Check H.V.
diode.
diode.
Abnormal
Defective high
voltage capacitor.
voltage capacitor.
Replace high
voltage capacitor.
voltage capacitor.
Check H.V.
capacitor.
capacitor.
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)
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