Crumar Musical Instruments User Group.

Greetings,

I have two Crumar Bit One keyboards that have bad voices.  One has
three working voices, and the other has a single working voice.  I do
have schematics and board layouts, but have not been able to get
anywhere with them.

The two Bits are different revisions, one with CEM3328 and the
other with SSM2044 filters.  The circuit boards within each are not
interchangeable.

I do have a meter and a scope, but haven't been able to determine
which (if any) signal paths may be defective.  My knowledge of
electronics is basic, so while I can replace parts and generally poke
around with a meter, I don't know how to diagnose with the scope
beyond looking at the waveform going in and out of chips.  I haven't
yet located the lack of signal that would indicate failures.

I do have a few spare filters of each type, but it appears that the
problems with these are not the filters, since no matter how I swap
and change them around, the bad voices are always in the same place,
such as 1,5,6

I also tried rearranging some of the other socketed ICs, and swapped
common ones from one board to the other, but the problem does not
change at all.  It seems that both boards may have the same problem
(missing, non-filter related voices) but I'm definitely lost.

Any suggestions or insights would be appreciated, in particular, what
sorts of parts are likely to fail on these instruments.  These were
unused for over a year, due to these problems, only more voices have
failed as time has gone on.  I would very much like to get at least
one of these working again.

Thanks very much for your consideration.