Panasonic TH-37PX60U, Technical Manual

Page: 42 / 98

F+15V, DTV9V, SUB5V SOS Detect Circuit
The F+15V, DTV9V, and SUB5V are monitored for over-voltage and over-current conditions by the SOS
circuit on the A board.
Under normal condition, pin 114 of the main CPU (IC1100) is low. When a short circuit or an over-voltage
condition occurs, the SOS detect circuit is triggered causing pin 114 to go high. When pin 114 goes high, the
TV shuts down and the power LED blinks 10 times.
When the F+STB15V line is shorted, the base of Q3503 goes low turning it on. When Q3503 is on, a high is
applied to pin 114 of IC1100 triggering the shutdown operation.
The same will happen if a short circuit develops in the DTV9V line and the SUB5V line.
The transistor Q3505 monitors the SUB5V and the DTV9V lines. If any of these supply voltages becomes
excessive, the inline zener diode (D3505 or D3506) goes into conduction and turns on transistor Q3505. As a
result, a voltage drop appears at the base of Q3503, causing it to turn on and output a high to pin 114 of the
MPU, IC1100. The MPU shuts down the unit.
42