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7.2. (Troubleshooting) Other problems
SYMPTOM CAUSE CORRECTIONS
1. Oven is dead. 1. Open or loose lead wire harness
Fuse is OK. 2. Open thermal cutout / thermistor Check thermal cutout is defective.
No display and no operation at all. 3. Open low voltage transformer
4. Defective DPC
2. No display and no operation at all.
Fuse is blown.
1. Shorted lead wire harness Check adjustment of primary, secondary latch
switch and short switch including door.
2. Defective primary latch switch (NOTE 1)
3. Defective short switch (NOTE 1)
4. Defective Inverter Power Supply (U)
NOTE 1:
All of these switches must be replaced at the same time.
Check continuity of power relay RY1 contacts (between 1 and 2) and if it has continuity, replace
power relay RY1 also.
3. Oven does not accept key input
(Program)
1. Key input is not in proper sequence Refer to operation procedure.
2. Open or loose connection of membrane key
button to DPC (Flat cable)
3. Shorted or open membrane key board
4. Defective DPC Refer to DPC troubleshooting.
4. Fan motor turns on when oven is
plugged in with door closed.
1. Misadjustment or loose wiring of secondary
latch switch
Adjust door and latch switches.
2. Defective secondary latch switch
3. Door switch CN12
5. Timer starts count down but no
microwave oscillation.
(No heat while oven lamp and fan
motor turn on)
1. Off-alignment of primary latch switch Adjust door and latch switches.
2. Open or loose connection of high voltage
circuit especially magnetron filament circuit
NOTE:
Large contact resistance will cause lower
magnetron filament voltage and cause
magnetron to have lower output and/or be
intermittent.
3. Defective high voltage component
H.V. Inverter Power Supply (U)
Magnetron
Check high voltage component according to
component test procedure and replace if it is
defective.
4. Open or loose wiring of power relay RY1
5. Defective primary latch switch
6. Defective DPC or power relay RY1 Refer to DPC troubleshooting
6. Oven can program but timer does not
start countdown.
1. Open or loose wiring of secondary latch switch
2. Off-alignment of secondary latch switch
3. Defective secondary latch switch
7. Microwave output is low. Oven takes
longer time to cook food.
1. Decrease in power source voltage Consult electrician
2. Open or loose wiring of magnetron filament
circuit.(Intermittent oscillation)
3. Aging change of magnetron
8. Fan motor turns on and turntable
motor rotates when door is opened.
1. Low voltage transformer on DPC.
9. Oven does not operate and return to
plugged in mode as soon as [Start]
button is pressed.
1. Defective DPC Check grounding connector on escutcheon
base.
10. Loud buzzing noise can be heard. 1. Loose fan and fan motor
11. Oven stops operation during cooking. 1. Open or loose wiring of primary and
secondary latch switch
Adjust door and latch switches.
2. Operation of thermal cutout
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NN-SD452W / NN-ST462M / NN-ST452W