[sdiy] Oberheim 4-voice issues (SEM, keyboard)

[Oakley Sound]

The most common cause of SEM VCOs going high frequency that I have found 
is, in order of likelihood:

1. Dead 3086 (we know it's not that though)
2. Dead timing cap
3. Dead temp co

Although, since both VCOs are dead this does seem to indicate another 
possibility. Having two dead temp cos (or dead polystyrene caps) does 
seem somewhat unlucky.

The timing cap is an easy check though. Just bung another 1nF cap across 
the existing cap and see if the VCO drops to audio frequencies.

Tony

www.oakleysound.com