Intermittent loss of sound output on Denon D-C1

I switch it on and one of two things happens. Either its fine, or I get no sound out from it. Then the next day it works fine again - or maybe it doesn't. When the sound stops, it stops on both left and right channels. I get no output from CD or radio or tape so it looks like the problem is in the audio amplifier stage. Volume control rotates but has no effect. There is nothing audible from the speakers. The display light etc are on so the PSU is presumably OK. Powering on-off doesn't fix it. I waited till it stopped working, and opened it up and "wiggled" all the connectors but it made no difference then, or after reseating them. I cannot see any dry joints, split tracks or burned components by quick inspection. I think I may have started it working after tapping it strongly suggesting an intermittent or dirty contact, or a split track in a PCB. If so, it affects both left and right channels so it must be somewhere where one fault stops both channels. I can borrow an oscilloscope :-) but I don't have a circuit diagram :-(. A circuit diagram would be fantastic or even hints as to how it works, or which components are which - eg which is the amplifier(s), or a circuit diagram of a system which uses the same audio chip(s) so I at least have an audio circuit to work from. WHat is the chip set number? I am thinking of following the audio signal from the volume control. Does anyone know how the volume control works? Does the audio signal appear across the volume control, and a proportion is fed into a constant-gain amplifier from the wiper? Or does the audio NOT appear across the volume control, and instead goes direct into the amp, and the volume control provides a control signal to the amp varying its gain? If anyone can help I will be very grateful. It's probably not worth paying to get it repaired as it would cost more than a new one, but I hate to be beaten by what must be a really simple fault.