X-Ray Protection Circuit - Toshiba TW40F80 Technical Training Manual

N5ss chassis projection television

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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

and C471 in X-RAY protection circuit rises. When E

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.

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-

rectified by D471

rises,

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:

Fig. 9-23 X-RAY protection circuit

• To restart TV set, repair failure first.

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