John Lewis NN-GT578SBJQ OEM 27L JLFSMWG002 Service Manual page 21

H97, H98 appears in
the display window.
Check oven input
current.
More than 0.5A
Check magnetron
filament continuity.
Refer to component
OK
test procedures
12.6 Digital programmer circuit troubleshooting
SYMPTOM
No display when the microwave
oven is first plugged in.
Microwave oven is dead
NOTE
The procedure for repairing the fuse pattern on the DPC is as follows:
1. Fuse pattern PF2 open circuit
a) Remove the jumper wire PF2
b) Move the jumper wire PF3 into the postion of PF2 and solder inplace.
Replace the DPC if both the fuse pattern PF2 and PF3 are open circuit.
Note: After repairing the fuse pattern on the DPC, check the varistor for any burns and measure the winding
resistance of the low-voltage transformer primary coil.
No key input
No beep sound
Power relay (RY2 ) does not
operate
No microwave oscillation
Dark or unclear display
Missing segments in display
DPC board/Power Relay
Less than 0.4A
Loose wiring.
Latch Switch.
DPC control signal
Open
Magnetron*
Stop!!
If all the preuious checks
are OK, there may be an
H.V. Inverter fault.
NOTE:
STEP CHECK
1 Fuse pattern on DPC
2 IC10 pin 9
12V line
3 IC-1 pin 73
(Emitter of Q10)
4 IC-1 pin 27
(pin 15 of IC220)
1 Push button switch
1 IC1 pin 12
1 IC-1 pin 23 during
operation
2 Create a short circuit
between pin 6 and pin
16 of IC-2
1 IC-1 pin 18 and 16
during high power
operation
2 Q221 transistor
1 Replace display
Replace IC-1
DANGER
HIGH
VOLTAGE
*Check the continuity of the magnetron
filament. Check the fialment is not shorted to the
magnetron case..
NOTE:
power supply.
THE PRESET VOLUME
board. It is very dangerous to repair or adjust this
preset without correct test equipment.
Do not attempt to repair the inverter circuit board,
replace the inverter circuit board with a new unit.
RESULT
Normal
Open (Note1)
Abnormal 0V
Normal 12V
Abnormal
Normal 5V
Abnormal
Normal
Abnormal
Normal
Abnormal
Normal
Abnormal
Normal 5V
RY2 does not turn on RY2
RY2 turns on
Abnormal
Normal 18 - 5V
16 - 5V
Abnormal
Normal
Abnormal
Normal
21
DO NOT REPAIR
try to the inverter
DO NOT ADJUST
on the inverter circuit
CORRECTION
STEP 2
Shorted circuit ZNR-
LVT-Lamp
IC10
Step 3
ZB10 Q10 Ribbon cable
Step 4
IC-220
IC1 CX1
Push button switch
IC-1
IC-1
IC-220 BZ310
IC-220
IC-1
Step 2
Display
IC-1
IC-1
Display