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ii
2-4 Protection
circuit
L
This chassis employs two kinds of protection circuit, one controlled by software through the
CPU and the other by hardware.
L
Protection circuit (software)
The protection circuit is provided to disable the operation of the TV set in case of a circuit
malfunction.
When an abnormality
occurs during TV reception it causes pin 41 of the CPU to go con-
tinually Low (less than 0.8V) for about one second. The CPU detects that this has
occurred and outputs the signal to cut off Q683 and Q684.
Protection circuit (hardware)
When a power failure is detected by diodes D643, D644 and D645, this protection circuit
operates causing the power oscillation to stop.
If one of the above diodes is turned on, the voltage of Q631 -emitter decreases,
and it
turns on completely. Photo-coupler
D615 is driven by this and generates a current which
drives Q612 on. As a result, the operation of the power oscillation circuit is stopped.
Under normal circumstances
these parts, D615, Q631, D641, R635, R636, VR631 are
operating as the error detection and regulation circuit for +130V power supply.
D445
Heater
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130V
Regulator
circuit
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power
15k
iAA
operation ~ failuer
Training
Manual
AC 1Chassis
-11-
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