Stahl-tek Vekian - help please!

I have a Stahl-tek Vekian DAC which has hit a problem. The guy trying to fix it for me is "flying blind" with no circuit diagrams or anything to guide him. Does anyone know where he can access some technical data to help fix the problem? (basically a crackle and hiss emerging from the right output channel)

There is a Facebook page but no apparent activity on it to help, so any suggexstions gratefully received....