A Board Sos Detect (Explanation) - Panasonic TH-42PX80U Service Manual

A board SOS Detect (Explanation)

10 Blinks SOS: The voltage regulators IC5400 and IC5401 in the A board generate SUB9V and
SUB5V. The 9V and 5V from these ICs are monitored by IC1100. Any abnormality on the SUB9V or
SUB5V lines, triggers the shutdown circuit and the MPU shuts down the unit. The power LED blinks
10 times.
11 Blinks SOS: The ventilation fans are monitored for proper operation. If one of the fans opens or
increases resistance, the resulting current change is applied to pin 61 of the main CPU. This triggers
the Fan SOS and the TV shuts down. The power LED blinks 11 times.
To prevent the TV from shutting down when one of the fans is disconnected, a jumper should be
placed between pin 2 and pin 3 of the missing fan connector.
12 Blinks SOS: On the A board, transistor Q2301 monitors the Sound 15V line and the operation of
the audio power amplifier IC2301. If the audio output circuit, IC2301, or the 15V lines develops a
short to ground, transistor Q2301 goes into conduction and applies a high to pin 70 of the MPU,
IC1100, triggering a SOS condition. The power LED blinks 12 times.
A short circuit in the sound P15V normally shuts the TV down and the power LED blinks 2 times. It
can also cause the TV to shutdown and make the power LED blink 12 times.
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