Problem with threshold S-150

[Victorinox]

I have one channel outputting 18VDC and no idea where to start troubleshooting.
Any help greatly appreciated.

 

[Zen Mod]

start with well lit and big pictures, some (recent) history and fact - do you have appropriate schm, or not

 

[Victorinox]

start with well lit and big pictures, some (recent) history and fact - do you have appropriate schm, or not

Amplifier hasn’t been touched from what I can see.
Schematics I found in another thread on here but barely readable.

 

[Victorinox]

One ch 16 millivolts. Another 18 volts.

 

[Victorinox]

One channel works and sounds fine.