John Lewis NN-GT578SBJQ OEM 27L JLFSMWG002 Service Manual page 18

12.1 Troubleshooting (no operation)
Symptom
1. Oven is dead.
Fuse is OK
No display and no operation at all.
2. Oven does not accept key input
(Program).
3. Oven lamp and turntable motor turn
on when the microwave oven is
plugged in with the door closed.
4. Timer starts to countdown but no
microwave oscillation.
12.2 Troubleshooting (fuse blown)
Symptom
1. No display and no operation at all.
10A Fuse is Blown
Cause
1. Open or loose lead wire harness.
2. Open low voltage transformer.
3. Defective DPC AU or DPC DU
1. Key input is not in sequence.
2. Shorted push button on DPC AU
3. Defective DPC AU.
1. Maladjusted or loose wiring of
secondary latch switch.
2. Defective secondary latch switch.
1. Maladjusted latch switches.
2. Open or loose connection of high
voltage circuit, including the mag-
netron filament circuit.
NOTE: A large contact resistance
lowers the magnetron filament volt-
age reducing the magnetron output
or causing intermittent operation.
3. Defective high voltage component
Inverter circuit or Magnetron.
4. Open or loose wiring of power
relay (RY1)
5. Defective primary latch switch.
6. Defective power relay RY1 or DPC
AU or DPC DU.
Cause
1. Shorted lead wire harness.
2. Defective primary latch switch
(NOTE 1)
3. Defective short switch (NOTE 1)
4. Defective Inverter power supply.
(Refer to inverter circuit test pro-
cedure on page)
NOTE 1: All of these switches must
be replaced at the same time. (Refer
to adjustment instructions page)
Check continuity of power relay RY1
Replacce this relay if it is short cir-
cuit.
18
Correction
Refer to operation procedure.
Refer to DPC troubleshooting
Adjust door and latch switches.
Adjust door and latch switches.
Check high voltage components
according to the component test
procedure.
Correction
Check adjustment of the Door, Pri-
mary, secondary and short latch
switches.