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19. RA-5A High Voltage Circuit Troubleshooting
Chapter 19 - RA-5A High Voltage Circuit Troubleshooting
FIGURE 19-1 - HIGH VOLTAGE STAGE - RA-5A CHASSIS
T8005
FBT
IC8007
PROT. 1
Q8028-9
ABL
DRIVER
Q8004
Q8016
Q8019
Q8020
H DRIVE
Q8023
H OUT
REG.
Q8027
DRIVER
Q8036
Q8037
IC8008
PWM GEN.
1
10
3
3
C8118
LOT
T8004
1
14
12
12
1
6
2
2
4
1
HV BLK
7
VIDEO
OUT B+
C B BD.
14
10
10
9
IC3006
VIDEO
PROCESS
40
7
3
5
IC8006
PROT. 2
5
3
2
D8025
D8023
+12V
CN8016
CRT
HV
R8171
100
+135V
D8036
15V
MIX OUT TO
IC8007
Q8035
HV REG.
P
CH
CN6106/
CN8013
CN8004/
CN3005
CN3007/
CN8006
V BD.
VEL MOD COILS
CN3023/
CN9001
CN3010/
CN9001
CN3001/
CN9001
+135V
SEC.P.S
IC6001
(G BD.)
D8039
200V
R8219
D8038
R8223
CN8022/
CN7304
D8029
D8030
C8142
ABL
R
R8153
PROT.
VR8002
100k
D8017
N
D8031
18V
D8034
D8035
R8160
R8198
10k
Q8021
Q8022
DRIVERS
Q8005,
Q8032
+15V
CN8021
A BD.
G BD.
D BD.
Q8038
HV OUT
D BD.
+135V
+135V
7/17/02
19.1TVP14
1
1
1
200V TO
R8196
8.1V
7.46VDC
7
11
S
D
G
D8015
LATCH
18
6
VR8001
5k
HV
1
1
Overview
Figure 19-1 illustrates a block diagram to give an overall view of the circuitry on the D board for generating high
voltage. The main components consist of a regulator stage to vary the B+ level to the flyback transformer for HV
level control, a driver and output stage to switch the flyback on and off, a flyback transformer to generate HV and
a LOT transformer to generate heater voltage and 200VDC for CRT cathode bias.
IC8008 is a PWM generator and driver to control the on and off time of HV regulator Q8035. The sawtooth
waveform for the PWM generator is synchronized to the horizontal drive pulse at pin 14 to provide a stable
reference. A sample of HV level is taken from the HV block assembly and enters pin 12 to provide an error loop
by which to vary the duty cycle of the drive pulses to Q8035. Q8038 provides the necessary switching to turn
T8004 and T8005 on and off and maintain a HV level of 31KV.
HV level and current are monitored by IC8006 and IC8007. They will stop high voltage generation to provide
protection for the HV components, CRT’s and X radiation level. This is accomplished by disabling the H drive
pulse from video process IC3006. Both the HV level and shutdown threshold are shown as adjustable by
VR8001 and VR8002 but these controls are sealed with epoxy at the factory and are not adjustable.