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11. RA-4/4A High Voltage Circuit Troubleshooting
3
2
1
2
3
1
2
3
1
FIGURE 11-5 - HV STOP 1
R8176
+12V
Q8027
FROM
HV STOP 2
ABL
R8170
C8092
D8036
R8116
C8071
C8062
R8106
R8115
+12V
Q8023
P
D8024
FROM
IC8007/7
REGULATION
CONTROL
C8059
5.9V
IC8010
R8111
9.3V
D8025
+12V
C8065
D8030
IC8008
7.4V
+12V
R8107
5.1V
+135V
R8134
R8133
R8182
C8072
D8031
4.6V
D8027
R8091
R8087
+12V
R8102
C8060
IC8006
R8120
C8078
R8137
Q8019
TO
D8021
OR
HV STOP 2
C8053
N
TO HD
BUFFER
Q8005/B
11.5TVP14
6/3/02
HV Stop 2: Referring to Figure 11-6, the second HV protect circuit is shown. It functions in a similar manner as
HV stop 1 with a few differences. Q8031 monitors voltage from the flyback transformer rather than the HV block
assembly. Pin 5 of IC8010 will receive this signal and, instead of comparing it to a fixed reference, the ABL
voltage is used. The reason behind this design is to shut down the high voltage quickly if it is rising and flyback
current is simultaneously increasing. This severe condition can damage multiple components. The ABL voltage
at pin 6 will drop, while the HV sample at pin 5 increases. Q8028 will monitor flyback current in the same manner
as HV stop 1.