Without a scanner anymore I will have to type this out. I hope Frank does not mind, I'm just trying to help. There is no schematic but some of this might help you in your repair if your going the DIY route; here goes.....April 1,1981.
The MOS-FET control amplifier SCA-80 is a combination of the MOS-FET 80C circuits and Super FET PAT-4 Series 2 preamp circuits built into either a SCA-80 or SCA-80Q integrated amplifier chassis, complete with precision volume and balance controls and a new power supply.
The new PC cards contain a simple, but eloquent three transistor Class A voltage amplifier circuit of all new design. Each devise has an independent current regulator for outstanding power supply rejection, the front end cannot overload or slew limit on any signal slope( the amplifier has an infinate slew factor). Each channel has trim pots for adjusting bias current and DC centerline for maximum power and symetrical clipping. Gain set and pole determining components are installed in matched pairs for exact channel balance.
The current amp is a complementary pair of Hitachi 2SK133 and 2SJ48 power MOS-FET devices. They are each rated at 100 watts, 120 volts, and 7 amps and thus cannot be over driven in this circuit. Because the current amp has high input impedence, no driver transistors are required. V1 limiting, thermal bias tracking,and output coils are unnecessary and are not used.
The power supply is a stiff unregulated 70 volt DC supply, with a seperate supply for the voltage amplifiers, and additional decoupling and regulation at the cards.
Well thats all I can dig up for right now. It's above me but I hope might be of some use to you guys. I loved that amp....Mark Korda.