Furuno FS-1570 Service Manual page 150

5.5 Power Amplifier (PA)
TEMP signal
The thermistor RT1 detects the temperature of power amplifier. When the temperature
increases up to about 80 °C, "TX POW REDUCED MAIN AMP HEATED" appears
and the power is reduced automatically.
PA ON signal
PA ON signal switches on/off the DRV and PA bias circuits on PA board.
Fig.5.5.2 PA frequency characteristic of FS-1570
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