Sony KDP-57XBR2 Training Manual page 42

The other lines monitored are not detected by IC1009 and, therefore, will not be indicated by the self-diagnostics.
Figure 9-2 provides a detailed view of these. This includes over-current (or loss of) the +19, +22 and +7 volt
lines. The 11V is protected against over-voltage. The base of Q6101 is kept high by the 11V line through R6133.
If the +19V or +22V drops below 11.5V, diodes D6122 and D6125 will forward bias, pulling Q6101 base down and
turning it on. This will activate the relay latch circuit (Q6102 and Q6103). The same will occur if the +7V is lost
by causing D6121 to fire. If the +11V line rises to 15.1V or more, D6121 will also participate by firing and holding
the base of Q6101 steady while the emitter rises. This will also turn on Q6101 and the latch circuit.
Most protect circuits that monitor multiple lines are arranged in this manner. Troubleshooting consists of checking
the voltages across the blocking diodes. Since they are normally reverse biased, the voltages across them will
be greater than .6V. Even a DVM without peak hold can detect this. For example: If the +19V failed, the meter
would read a maximum of 0.6V across D6122. Under normal conditions, approximately 8.5V would appear. By
monitoring blocking diodes for 0.6V and zener diodes for their rated voltages, one can test each of these while
turning the set on and quickly locate the source of the protection event.
Another useful tip when working on shutdown events is to monitor the AC current draw with the variac. Large
current spikes will assist in determining if an over-current condition exists, and helps to decide which areas to
check first. When working on direct-view televisions, be sure and disconnect the degauss coils to get an accurate
assessment since they draw large amounts of current. Even if the diagnostic feature is indicating an over-
current protection, it is wise to check the AC current draw when turning the set on. This helps to determine if
there is an actual current problem. Sometimes the circuits that monitor the current will fail and cause a shutdown
event even though one does not exist. The block diagrams illustrated in this manual will assist in locating
shutdown sources within minutes.
FROM RM+5V
R6110
D6101
FROM
R6102
+135V
3
IC6103
REF. VOLTAGE
uPC1093J-1T
2
C6103
R6103
R6101
R6104
FROM
T6001/7
R6118
+19V
+22V
+7V
2.25V
8
5
6
OVP
2.4V
1
IC6102
OVP/OCP
uPC393C
0.2V
OCP
2
3
4
C6102
C6108
11.5V
R6106
D6122
R6105 D6125
D6121
MTZJ - 7.5B R6132
FIGURE 9-2 - DC PROTECTION
R6143
7
R6142
1
D6124
D6123
R6113
Q6101
R6134
P
R6120
C6140
11.5V
R6133
39
9. RA-4/4A Protect Circuit Troubleshooting
CN6101
5 B+OVP
6 B+OCP
4
PROTECT
3
RELAY
R6112
R6121
Q6104
D6111
R6125
P
Q6102
R6126
R6117
N
Q6103
IC6011
VCC SW.
PC123FY2
C61115
G BOARD
TO
A BD.
CN505
D6112
N
2 1
3 4
TO
VCC SW.
TO
SOFT
START
FROM
11V
9.2TVP14 5/23/02