4.4. Trouble related to Digital Programmer Circuit
4.4.1. NN-ST657S, ST657W
SYMPTOM STEP CHECK RESULT CAUSE/CORRECTIONS
No display when oven is first plugged
in
1 Fuse pattern of D.P.C. Normal →Step2
Open Replace D.P.C. or Fuse
Pattern
2 Low voltage transforment (L.V.T.)
secondary voltage
Abnormal 0V L.V.T.
Normal →Step3
3 IC1 pin23 voltage Abnormal Q11, ZD11, Q10, ZD10
Normal=3.3V IC1, CX320, Display
No key input 1 Membrane switch continuity Abnormal Membrane switch
Normal IC1
No beep sound 1 IC1 pin 29 voltage Abnormal IC1
Normal=3.3V BZ210, Q210
Power relay A(RY2) does not turn on
even though the program had been set
and the start pad is tapped
1 IC1 pin 2 voltage while operation Abnormal IC1
Normal=3.3V →Step2
2 Collector of Q225 Abnormal Q225
Normal 0.7V RY2
No microwave oscillation at any power 1 IC1 pin 1 voltages while operation at high
power
Abnormal IC1
Normal=3.3V →Step2
2 Collector of Q224 Abnormal Q224, Q231
Normal 0.7V →Step3
3 Short circuit between collector of Q227
and emitter of Q231
Still not turn on RY1
RY1 turns on Q220, Q222
Dark or unclear display 1 Replace display and check operation Normal Display
Abnormal IC1
Missing or lighting of unnecessary
segment
1 Replace IC1 and check operation Normal IC1
Abnormal Display
H95/H97/H98 appears in window and
oven stops operation.Program High
power for 1 minute and conduct
following test quickly, unless
H95/H97/H98 appears and oven stops
1 Unplug CN702 (2 pin) connector and
measure voltage between terminals
Abnormal=0V 1. Latch Switch
2. D.P.C. /Power Relay
Normal=220~240V →Step2
2 Unplug CN701 (3 pin) connector and
measure pin3 voltage
Abnormal=0V D.P.C.
Approx. AC 3V Magnetron
12
NN-ST657S / NN-ST677M / NN-ST667W / NN-ST657W
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