Panasonic TC-L42D2 Technical Manual page 54

3 and 7 Blinks SOS Circuit
The A Board is responsible for the regulation, distribution and dissemination of all secondary
voltages derived from the DTV12V output of the P Board. When the unit is powered, the 12V
output of the P board biases the transistor Q5613 into operation, causing its collector to become
"low". As a result the transistors Q5612 turns off. The high at the collector of Q5612 causes
IC5606, IC5608, IC5610, and D5670 to operate and provide the SUB5V, 1.8V, 1.2V, and
SUB3.3V output.
If a malfunction occurs and the SUB5V, 1.8V, and 1.2V are not present, IC4700 detects the loss
of voltage and provides an output to IC8001 to shut the unit down. The power LED blinks 3 times.
The SUB3.3V is monitored directly by the CPU, IC8001. If it is shorted or missing, the unit shuts
down and the power LED blinks 7 times.
IC8001 turns off the AC power by disabling the SUB_ON command that turns on the AC relay.
Slide # 54