I was given a Technics SX-KN800 keyboard and am trying to repair it. I have
opened it up and the six or so PCB's are easy to get at. The symptom is no
audio. The PA thumps through the speakers on turn off and the PA has power
supply OK so it is not a concern at the moment. The line out has no audio
either. Of course it is possible that a crash has occured but I cannot find
a reset so far. No audio is getting to the PA. I could not find any signal
at the master volume either, though it may not have real signal at it.

I believe it was made early to mid 90's. There are a lot of Technics
proprietery chips in it. I have an op manual for a KN1000 which is similar,
but no schematics appear anywhere I have seen.

What I would like to know is a general question about how the audio signal
is generated from the PCM pulse stream. It may be a simple LPF from a
digital chip which regenerates the audio, or there may be a specialised
audio chip to look for? If I can't go much further I will have to junk it.