The PA receiver is housed at the toilet end of the coach behind the vestibule panel next to the lights switch.

The 24v positive supply comes from the RCH light control switch, as do the two RCH connections. The 0v is taken to a convenient light fitting. Coach saloon speakers are wired in series/parallel to present a load of 3 - 6 ohms to the receiver.

The circuit is a simple preamplifier (U1) followed by a fairly conventional power amplifier.  The power supply is overvoltage protected by D3 and D5, and reverse polarity protected by D6.

A repair service for these units is available from GoToPCs - just email me (see Home page)