Power / Stand-By Circuit; Protection Circuit - Sanyo FC3G2 Training Manual

2-3 Power On/ Stand-by circuit.
Power on / stand-by
The power on/stand-by signal is output from pin 31 of the CPU.
When the stand-by mode is selected the voltage of pin 31 changes from Hi(5V) to
Low(0V) to turn off Q681and Q652. Q652 turning off causes Q653 and
Q654 to turn off. +24V supply for vertical and horizontal output circuit, +9V supply
for IF/VIDEO/Chroma circuit and +5V for tuner circuit are all cut off, resulting in the
TV set going into the stand-by mode.
When the TV is switched back into the power on mode, Q681 and Q652 are turned
on and the relevant voltage are supplied back to each circuit.
Q681
IC681
Q652
Fig. of Power On/Stand by Circuit

2-4 Protection circuit

This chassis employs two kinds of protection circuit, one controlled by software through
the CPU and the other by hardware.
. 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 31 of
the CPU to go continually Low (less then 0.8V) for about one second. The CPU detects
that circuit malfunction has occurred and cut off the signal output to Q681.
. Protection circuit (hardware)
When a power failure is detected by diodes D655, D690 and D468, this protection circuit
operates causing the power oscillation to stop. If one of above diode is turned on, the
voltage of Q661-emitter decreases, and it turns on completely. Photo-coupler D610 is
driven by this and generates a current which drives Q625 on. As a result, the operation
of the power oscillation circuit is stopped. Under normal circumstances these parts,
D610, Q661, D661, R661, VR661, R662 are operating as the error detection and
regulation circuit for +130V power supply.
TO HEATER PROTECT
& HOLDDOWN CIRCUIT
TO VERTICAL
DEFL. CIRCUIT
(FOR PROTECTION)
TO CPU
TO IC201, IC281
AUDIO PROCESSOR,
AV SWITCH & CRT UNIT
TO VIDEO PROCESSOR,
TUNER & DEFLECTION
TO HOR & VER,
DEFLECTION CIRCUIT
TO AUDIO AMP. IC
TO TUNER AND
HOR DEFL. CIRCUIT
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Training Manual FC3G2 Chassis