Panasonic TH-65PX600U Service Manual page 27

STB5V and TV-SUB-ON function on the PA PCB
The STB 5V at pin 1 of connector PA40 and the TV SUB ON command at pin 33 of
connector PA20 are used to activate the PA SOS detect circuit on the PA board. This circuit
monitors the following voltages for abnormality: FTSB14V, SUB3.3V, SUB9V, SUB5V,
Main3.3V, and Main1.8V.
Under normal operation, the voltage from the voltage divider (R5694 and R5654) is enough
to turn on Q5604. When Q5604 is on, a low is applied to the base of Q5643 turning it on.
When Q5643 is on, 5V is applied to the collector and base of Q5641. The transistor remains
off until a short circuit is developed in the supply lines connected to its base.
When Q5641 is off, a low is output to pin 34 of PA20. This low is then applied to pin 209 of
IC1103 on the DG board through pin 7 of connector DG20.
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