Vintage Synth Repair

>I wonder if anyone could help with this one:
>
>On my OBXa, one voice card sound thinner than the others. When
>playing high notes this is less noticable but as going down the
>keyboard it goes and sound thinner, sort of like a high pass filter
>(no low frequencies). I tried to replace the CEMs but it's not in
>there...


It's difficult or impossible for anyone without intimate knowledge of the 
OBXa to suggest what to look for specifically.  What you need to think about 
is how to most efficiently analyze and approach the problem.  I would 
determine first if any parameters affect this by comparing pulsewidth, 
cutoff, resonance, etc. between the voice cards.  Then maybe I'd compare 
output waveforms or spectra for each voice to see if there's something more 
quantifiable, and find the source of the problem by tracing the signal path. 
  You probably don't even need an oscilloscope if you can use some sort of 
"audio probe" that goes straight into your sound card.

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