LG MB-394A Service Manual ▷ View online
5-10
COMPONENTS
TEST PROCEDURE
RESULTS
FUSE
HEATER ELEMENT
(Wire leads removed.)
(Wire leads removed.)
GRILL THERMOSTAT
OVEN THERMOSTAT
MAGNETRON
THERMOSTAT
MAGNETRON
THERMOSTAT
Check for continuity of the fuse with an
multi-meter.
multi-meter.
NOTE: If the fuse is blown, check the primary, the secondary, and the monitor
switches, H.V.D. and H.V.C. before replacing the fuse.
If the fuse is blown by improper switch operation replace the defective switch
and the fuse at the same time. Replace just the fuse if the switches operate
normally.
switches, H.V.D. and H.V.C. before replacing the fuse.
If the fuse is blown by improper switch operation replace the defective switch
and the fuse at the same time. Replace just the fuse if the switches operate
normally.
NOTE: Make sure heater is fully cooled when tested.
Measure the resistance.
(Multi-meter scale: Rx1)
(Multi-meter scale: Rx1)
Normal:
*Grill heater
*Grill heater
Approx. 50 ohm
(at 20 ~ 30
(at 20 ~ 30
o
C)
Normal: more than 0.5 Mohm
Normal Abnormal
Measure the resistance with 500V-100M ohm
insulation resistance meter.
insulation resistance meter.
0°C~Approx.90°C Approx.90°C
0°C~Approx.145°C Approx.145°C
5-11
COMPONENTS
TEST PROCEDURE
RESULTS
Disconnect the 8 pin
connector from P.C.B.
(Refer to schemetic diagram
on page 4-3)
connector from P.C.B.
(Refer to schemetic diagram
on page 4-3)
RELAY 2, RELAY 3
OF P.C.B.
(Wire leads removed.)
Note: Relay
Relay 1: Fan motor
OF P.C.B.
(Wire leads removed.)
Note: Relay
Relay 1: Fan motor
Turntable motor
Oven lamp
Oven lamp
Relay 2: Microwave
Relay 3: Grill
Relay 3: Grill
FAN MOTOR
(Wire leads removed)
(Wire leads removed)
TURNTABLE
MOTOR
(Wire leads removed)
MOTOR
(Wire leads removed)
Measure the resistance.
(Ohm-meter scale: R x 1)
(Ohm-meter scale: R x 1)
Measure the resistance.
(Ohm-meter scale: R x 1000)
(Ohm-meter scale: R x 1000)
Normal:
Abnormal: ∞ or several Ω
Normal: Approx. 100~200 Ω
Abnormal: ∞ or several Ω
Abnormal: ∞ or several Ω
NOTE : • A MICROWAVE LEAKAGE TEST MUST ALWAYS BE PERFORMED WHEN THE UNIT IS
SERVICED FOR ANY REASON.
• MAKE SURE THE WIRE LEADS ARE IN THE CORRECT POSITION.
• WHEN REMOVING THE WIRE LEADS FROM THE PARTS, BE SURE TO GRASP THE
• WHEN REMOVING THE WIRE LEADS FROM THE PARTS, BE SURE TO GRASP THE
CONNECTOR, NOT THE WIRES.
A
B
C
Cooking Start OFF
1
3
5
7
8
Relay 2
Relay 3
Cooking Start OFF
A ~ B A ~ C
30 ~ 50Ω 300~500Ω
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
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.
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