Panasonic TH-65PX600U Service Manual page 34

VSUS and VDA Circuits
The 3.2V from pin 17 of connector P25 is applied to the base of Q557 to turn it on. When
Q557 is on, a low is applied to the TV ON/OFF pin (20) of the POWER CPU (IC501).
When pin 20 goes low, pin 14 goes high to turn on Q551. When Q551 is on, it provides the
ground path to turn on the LED within the photocoupler IC507. The light from the LED
turns on the phototransistor within the photocoupler and its collector goes low to turn on
Q540. When Q540 is on, the DC voltage from the rectifier D586 is applied to pin 8 of
IC509. This makes pin 7 go high to turn on Q507.
Q507 outputs the VSUS. The VSUS is also used to turn on Q527 to generate the VDA.
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