User manual

TH-42PX25U 3.3V SOS detect
Pin 2 of the Microprocessor IC9709 on the D board, monitors the 1.8V_S, the
1.8V, and the 3.3V generated on the D board. It also monitors the P12V
(Unregulated. 14V) generated on the P board. The 12V(Unregulated. 14V) from
the P board is connected to pin 1 and pin 2 of connector D25.
If the voltage in any of these lines drops, the SOS circuit is triggered.
Under normal conditions, the voltage drop derived from the voltage divider
circuits at the base of Q9714, Q9717, or Q9716 is enough to turn the transistor
on. However should the voltage drop at the base of any of these transistors
decrease, the transistor is turned off. This allows the 5 volts at their collectors to
forward bias transistor Q9715. This effectively grounds pin 3 of the CPU (IC9709)
on the D board, triggering the shutdown circuit.
Under normal condition, pin 3 of IC9709 is set to high.
TH-42PX25U 5V SOS Detect Circuit (D board)
Pin 2 of the Microprocessor IC9709 on the D board, monitors the P5V from the P
board
If there is a short or the voltage goes low, the voltage drop derived from the
voltage divider circuit goes low and the SOS circuit is triggered.
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