I have a MCS 3225 from 1980 and it hums on all inputs. The Tape Input appears to have gotten shorted out with a CD player plugged into it. BAD Capacitors? Protection Circuit if there is one I don't know if there after the receiver is being played for a while will suddenly cut out not coming back for a long period of time.

It is always on the Left Speaker or left side of headphones. I know the receiver is not that great but good enough for a spare unit at 30 Watts RMS.