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frequency, and the turned waveform is shown in Fig. 11-17.
6. X-RAY PROTECTION CIRCUIT
1. Outline
In case picture tube using high voltage, when high voltage
rises abnormally due to components failure and circuit
malfunction, there is possible danger that X-RAY leakage
increases to affect human body. To prevent it, X-RAY
protection circuit is equipped.
2. Operation
Figure 10-18 shows the circuit diagram. Supposing high
voltage rises abnormally due to some reason, pulse at pin 9
of T461 also rises, and detection voltage Eb rectified by
D471 and C471 in X-RAY protection circuit rises. When Eb
rises, emitter voltage of Tr10 divided by R25 and R26 in
protector module becomes higher than [zener voltage (6.2V)
of ZD6 + Tr10 VBE ]. This causes Tr10 turns on to supply
base current to Tr9. Then Tr9 turns on. By this Tr6 and Tr6
turn on to make ON/OFF pulse at pin 7of QA01 in low level,
QB30 and Q843 turns off, then relay SR81 turns off. Tr6 and
Tr7 are in thyristor-connection, and 5V of power holds
protection operation until main power switch is turned off.
During circuit operation, power LED near main power
switch blinks in red. Caution : To restart TV set, repair failure
5V
MICOM
QA01#7
RB30
RELAY
SR81
Q843
QB30
15
R9
R10
Tr7
R21
Tr6
R12
C1
16
Tr5
R11
Figure 11-18 X-RAY protection circuit
12V
Tr10
Tr9
R20
R22
D3
12
+
C474
82
R472
R25
E
D
13
R26
C471
ZD6
T461
9
D471
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