Panasonic NN-T793SF APH Service Manual page 55

Trouble Related to Digital Programmer Circuit
SYMPTOM
No display when oven is first plugged in.
Oven is dead.
NOTE
Procedure of fuse pattern repairing is as follows:
1. When the fuse pattern (PF2) opens.
(1) Remove the jumper wire (PF1).
(2) Insert the removed jumper wire (PF1) to "(PF2)" position and solder it. If both "PF1" and "PF2" fuse patterns are open, please replace DPC.
2. When the fuse pattern (PF4) opens.
(1) Remove the jumper wire (PF3).
(2) Insert the removed jumper wire (PF3) to "(PF4)" position and solder it. If both "PF3" and "PF4" fuse patterns are open, please replace DPC.
NOTE:* At the time of these repairs, make visual inspection of the varistor for burning damage and examine the transformer with tester for the presence of layer short-
circuit (check primary coil resistance).
If any abnormal condition is detected, replace the defective parts.
SYMPTOM
No key input
No beep sound
Power relay A(RY-2) does not turn on
even though the program has been set
and the start pad is tapped
No microwave oscillation at any power
setting
Dark or unclear display
Missing or lighting of unnecessary
segment
H97/H98 appears in window and oven
stops operation. Program High power
for 1 minute and conduct following test
quickly, unless H97/H98 appears and
oven stops.
NEW H.V.
TO BE CONTINUED FOR SENSOR MODELS
Auto sensor cooking does not operate
normally.
(Steam Sensor cooking does not detect
steam from foods.)
STEP CHECK
1 Fuse pattern of DPC
2 Low voltage transformer (LVT)
secondary voltage
3 IC-1 pin 8 voltage
(Emitter of Q10)
4 IC-1 pin 10 voltage
(15 pin of IC-220)
STEP CHECK
1 Membrane switch continuity
1 IC-1 pin 31 voltage
1 IC-1 pin 32 voltage while operation
2 Short circuit between pin 6 and pin
16 of IC-220
1 IC-1 pin 38 and pin 39 voltages while
operation at high power
2 Q220 transistor
1 Replace display and check operation
1 Replace IC-1 and check operation
1 Unplug CN702(2 pin) connector and
measure voltage between terminals
2 Unplug CN701(3 pin) connector and
measure pin 1 voltage
1 Steam sensor terminal voltage by
using high impedance tester (20k Ω/
V), when breathe on metal surface of
sensor
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RESULT CAUSE/CORRECTIONS
Normal STEP 2
Open (NOTE) Shorted Circuit of ZNR,
L.V.T., Oven Lamp etc.
Replace DPC
Abnormal 0V LVT
➝ Step 3
Normal
Abnormal ZD10, Q10
➝ Step 4
Normal = 5V
Abnormal IC-220
➝ IC-1, CX320
Normal
RESULT CAUSE/CORRECTIONS
Abnormal Membrane switch
Normal IC-1
Abnormal IC-1
Normal BZ, IC-220
Abnormal IC-1
➝ Step 2
Normal = 5V
Still not turn on RY-2
RY-2 turns on IC-220
Abnormal IC-1
➝ Step 2
Normal
5---5V, 15---5V
Abnormal Q220
Normal IC-220, RY-1
Normal DISPLAY
Abnormal IC-1
Normal IC-1
Abnormal DISPLAY
1. Latch Switch
0V
2. DPC/Power Relay
➝ Step 2
AC line voltage of 120V
0V DPC
Approx. AC 3V Magnetron
Abnormal = 0V Steam sensor
Normal > 10~30mV IC-1