Sony KDP-57XBR2 Training Manual page 51

D BOARD
+135V
T8001
HDT
4
3
FROM
6
HV
DRIVE
7
2
1
C8014
Troubleshooting
Shorted HV Output Transistor: As with all horizontal output transistors, care must be taken to avoid failure of the
replacement part. Always check Q8008 since it can be easily damaged by the large current surge if Q8007
shorts. There is even the possibility that Q8008 was the cause of the failure. Disconnect or short the B-E
junction of Q8002. This will run the driver stage at low level. The output regulator will now try to compensate so
it must also be disabled. This can be done by unsoldering the gate of Q8008. The main relay can now be
jumped and power can be applied with the variac while monitoring the pulse at Q8007 collector. This is a little
extra work but it is better than losing the replacement part(s) and it is part of a critical safety circuit.
Place your scope probe somewhere near the HV output transistor or flyback. Most scope probes are not able to
handle the direct spike level from the flyback so this is a safe method. Just turn up the gain a little on the scope
and you will easily see the retrace pulse. Apply full AC power with the variac and watch for the pulse (assuming
it appears) before the circuit shuts down. If the flyback is defective, one of two waveforms is likely to appear.
The first may look like a sinusoidal waveform with a distinct ringing appearance. This definitely indicates flyback
problems. The second phenomenon will be a retrace pulse with a second, lower level, "phantom" pulse. It is
sometimes normal for this "phantom" pulse to appear at low B+ input levels but it should disappear quickly as you
increase AC voltage. Monitor the AC current level closely while doing this. If the phantom pulse remains and
current starts to rise, it is time to replace the flyback. One last situation that might occur is that the retrace pulse
looks great but as you approach higher AC input, it begins to jitter and dance on the scope screen. The current
will also be higher than normal. Back off the AC power quickly as this usually indicates excessive loading of
secondary lines. In this unit, it can be loads on T8002. Measure for shorts on the filament and 200V line. The
flyback T8003 only has two load circuits and they are the HV and focus blocks
T8002
LOT
Q8007
D8011
1
2
3
R8019
D8007
4
C8018
6
D8010
7
8
9
C8021
C8012
C8009
FB8001
Q8008
D8009
L8003
D8008
11. RA-4/4A High Voltage Circuit Troubleshooting
HEATERS
D8013
18
C8020
17
C8023
16
15
PS8001
R8039
R8038
13
12
R8199
D8014
11
L8004
10
D8003
R8012
FB8002
R8023
FIGURE 11-2 - HV OUT
48
R8183
R8200
C8025
R8016
R8020
H+
H-
210V
TO
HV
HV
BLOCK
1
2
T8003
FBT
3
4
5
6
TO
FOCUS
BLOCK
HV
7
8
9
10
12
ABL
(HV
11
STOP1)
NL8001
TO HV
C8032
STOP2
PWM
FROM
HV REG
11.2TVP14 5/30/02