High Voltage Circuit Troubleshooting - Sony KDP-57XBR2 Training Manual

Chapter 11 - RA-4/4A High Voltage Circuit Troubleshooting
Overview
The RA-4 chassis reintroduced the separate high voltage circuit that had been eliminated in the RA-2 and RA-3
chassis. This design offers better control of the high voltage level, resulting in more stable brightness and picture
size fluctuations. It is also a complicated circuit with regulation control and redundant protection circuits for over-
voltage and current problems. The circuit functions the same as a conventional horizontal/HV stage in most
televisions and troubleshooting is relatively the same. When regulation or shutdown problems occur, diagnosis
becomes more difficult because the circuit is critical for X-radiation control and to protect the small CRTs. The
anode cap is very close to the grounded mounting brackets and the deflection yoke. It can easily damage the
CRT if it leaks out of the anode cap.
Regulation is performed at the driver and output stages. Figure 11-1 illustrates the drive circuitry. The B+
supplying T8001 and Q8003 is varied by a PWM controlled regulation stage that controls Q8001 and Q8002,
which functions as a variable resistor across R8005 and R8007.
Figure 11-2 shows how the circuit is similar to flyback circuits found in other units and shows the regulation of the
output stage. The same PWM circuit that controlled the regulation in the drive section will control Q8008. This
FET will vary the ground return for Q8007 emitter. The circuit drives the flyback transformer, T8003 and T8002
that will generate the heater and 200V bias voltage for the CRT cathodes. The regulation and protect circuits will
be reviewed later in the troubleshooting of shutdown.
+135V
HV
R8024
REG
BLOCK
C8010
FROM HV
STOP 1&2
Q8019/C
Q8021/C
1
H
2
DRIVE
CN8003
JUMPER PLUG
R8002
D8002
D8001
R8123
Q8001
N
R8001
+12V
Q8005
R8011
R8015
R8010
11. RA-4/4A High Voltage Circuit Troubleshooting
D BOARD
R8004
1k
R8007
22k
R8005
22k
P
Q8002
N C8006
R8008
R8003
C8007
FIGURE 11-1 - HV DRIVE
47
R8009
C8008
Q8003
N
C8004
TO HV REG
BLOCK
T8001
HDT
4
5
6
TO
3
HV
OUT
2
7
1
PWM
11.1TVP14 5/29/02