[sdiy] OB-8 voice glitching, warble

[Eric Frampton]

What might cause a single OB-8 voice to make a very fast pitch warbling on both oscillators? Both oscillators modulate together. The individual VCO tune knobs on the front panel are still working, but they don't track the full 1V/octave on the keyboarfd.

I've tried replacing the 4051 and TL084 feeding TR3A and TR3B. Tried replacing the 4051 and TL084 feeding CV3. Just for grins, tried replacing the 4051 and TL084's on each side of VCO1F and VCO2F. Also happened to have a spare DAC and tried swapping that on the off-chance that it had failed.  No change in any case.

Also noticed that immediately upon first power up of the day it's in tune, then as it warms up it falls in pitch and goes into this warbly state.

Thoughts?

thanks,
eric