Tannoy Arena Sub schematics

Hi, I got a Tannoy Arena Subwoofer from a friend for repair. I managed to get the amplifier board out of the magnificent(!) box and also got the power supply out. When on there’s 7.7V between CD- and CD+. If the amp isn’t in standby I assume that should be much more. 

Things would get a lot easier from here if I got a service manual or schematics. Any hint will be appreciated! Tia Eduard. Power supplyPower supply