TH-42PD25U PA board SOS detect
Transistor Q7541 on the PA board monitors the UNR24V, the UNR10V, and the +9V. If
any of these supply lines develop a short circuit, transistor Q7541 goes into conduction
and applies a high to pin 69 of the MPU, IC001, through pin 33 of connector PA2 on the
PA board. This triggers the SOS circuit.
Transistor Q7544 monitors the +5V, and +2.5V line. If any of these supply lines increase
in voltage transistor Q7544 goes into conduction causing its collector to go low. As a
result, Q7541 conducts and applies a high to pin 69 of the MPU, IC001, through pin 33
of connector PA2 on the PA board. This triggers the SOS circuit.
The main +9V, the VD1+5V, the main 5V, and the main +2.5V are also monitored for a
drop in voltage. A decrease in any of these two supply lines forces the respective diode
to conduct and trigger Q7542. A high is applied to pin 69 of the MPU, IC001, through
pin 33 of connector PA2 on the PA board. This triggers the SOS circuit.
Note: This circuit is identical to the circuit used in the TH-42PX25U-P model.
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