Toshiba TW40F80 - Manual (Page 79)

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Then Q463 turns on. By this Tr6 and Tr6 turn on to make
ON/OFF pulse at pin 7of QA01 in low level, Q846 and Q845
turns off, then relay SR81 turns off. Tr6 and Tr7 are in thy-
ristor-connection, and 5V of power holds protection opera-
tion until main power switch is turned off. During circuit
operation, power LED near main power switch blinks turn
on and off in red.
Caution:
• To restart TV set, repair failure first.
7. X-RAY PROTECTION CIRCUIT
7-1. Outline
In case picture tube using high voltage, when high voltage
rises abnormally due to components failure and circuit mal-
function, there is possible danger that X-RAY leakage in-
creases to affect human body. To prevent it, X-RAY protec-
tion circuit is equipped.
7-2. Operation
Figure 9-23 shows the circuit diagram. Supposing high volt-
age rises abnormally due to some reason, pulse at pin 9 of
T461 also rises, and detection voltage E
D
rectified by D471
and C471 in X-RAY protection circuit rises. When E
D
rises,
emitter voltage of Q464 divided by R459 and R462 becomes
higher than [zener voltage (6.2V) of D458 + Q464 VBE ].
This causes Q464 turns on to supply base current to Q463.
Fig. 9-23 X-RAY protection circuit
RELAY
SR80
Q846
Q845
Tr5
Tr6
Tr7
R11
R12
R9
R10
R19
C1
C894
R879
R467
12V
D459
R468
C458
R458
R462
R459
Q463
Q464
C471
R472
D471
9
T461
D458
14
17
16
Z801
C459
5V
E
D
15