Panasonic TH-37PX50U Technical Manual page 19

The high command at pin 17 of connector P25 is applied to pin 18 of MC701 of the P
board. Pin 11 switches from 5V to 1.3V, and pin 12 from 15V to 0V.
The 1.3V at pin 11 causes Q551 to turn on and output 5V. The 5V is applied to pin 22 of
the "Drive Voltage Oscillator" MC303. It is also applied to the "Fan SOS" circuit of the
PB board via pin 4 of the connector P30. (See Fig 14.)
The 5V on pin 22 of IC MC303 causes it to operate. IC MC303 then turns on the Vsus
power supply circuit (MC301) and the Vda power supply circuit (IC301, and T301).
Vsus is output to SC and SS-boards. Vda is output to the Data Drive Circuit boards via
the SC board.
The low from pin 12 is used to turn on Q453, and Q451.
When Q453 is on, it outputs 12V to the PB board and the D board.
When Q451 is on, it outputs 15V to the PB board and the SC board
14