Panasonic Generation Plasma Display Television Technical Manual page 29

Main CPU VCC Supply (A Board)
On the A board, the STB5V is applied to pins 3 and 4 of the 3.3V regulator (IC5604). Pin 4 is the voltage
input to the IC and pin 3 is the ON/OFF command. The STB5V at pin 3 allows pin 5 to output 3.3V. The 3.3V
from IC5604 is then applied to pins 31, 50, 74, 78, 81, 85, and 100 of the CPU (IC1100). This turns on the
main CPU (IC1100) and a high command (TV_SUB_ON/TUNER_SUB_ON) is output on pin 1.
This command splits in 2 (TUNER_SUB_ON and TV_SUB_ON).
The TUNER_SUB_ON command together with the STB5V is applied to the "SOS detect circuit" to monitor
the sub voltages generated in the A board.
The TV_SUB_ON command is applied to the power supply board (P board) to create the F+15V.
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