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2-10
Power
On/stand-by
and Protection
circuit
Power On/Stand-by
The power on/stand-by
signal is outputted from pin 48 of CPU.
When the stand-by
mode is selected
the voltage
of pin 48 changes
from Hi(5V) to
Low(OV), which turns Q792 off and Q793 on. Q793 drives the photo-coupler
D315 which in
turn drives Q312 on. Finally Q312 stops the oscillation
of power circuit switching the TV
into the stand-by condition.
At the same time, Q793 drives the LED, D1 120 to illuminate
and indicate the stand-by
mode.
Protection circuit
A protection circuit is provided to protect the TV set in case of a circuit malfunction.
When an abnormality
occurs during
TV reception
it causes
pin 31 of the CPU to go
continually
Low (less than 2.OV). After one second, the CPU detects that a power failure
has occurred on the TV set, and the CPU turns the TV into the stand-by condition.
CPU
POWER 48
31
PROTECT
IN
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Power
Oscillation
Circuit
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Stand-By
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D362
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