Panasonic TH-37PX50U Technical Manual page 15

Figure 8
The power control IC, MC701, upon receiving the "F.STB ON" voltage, outputs the "PC
PFC ON" control signal at pin 20. This turns on the photocoupler PC503 to provide a
low to pin 2 of the "STB Power Control" IC, MC501. MC501 outputs the "relay ON"
control signal to activate the relay K601. (See Fig. 8)
Figure 9
The rectifier MC604 rectifies the 120VAC from the relay and outputs to the "PFC
Control" MC602.
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