I posted this message to VintageSynthRepair earlier, but have since
discovered this group and thought I join. Apologies for the cross-post
if you're subbed to both.

Recently I acquired a "troubled" Oberheim OB-8 (non-MIDI, firmware rev.
A8). It's behavior is very erratic, but the one symptom that is
consistent is that when using the frequency adjustment for OSC 1 or 2 in
any voice, or the Master Tune control, the pitch change is not smooth,
but rather extremely glitchy. What follows are the tests I've performed
so far, and their results.

*Verify voltage sources at connectors I and J: In spec
*DAC calibration: In spec
*Oscillator volts per octave adjustment: I was able to get the
adjustments for oscillators 1 & 2 in spec (both test LED's lit), but in
every case the adjustment was extremely sensitive and it was difficult
to get both LED's to stop flickering. When performing the adjustment
for F-ENV modulation (T102, T202, etc) on voices 1-4 (lower board) only
test LED 1 was illuminated regardless of trimmer setting; I couldn't get
LED 2 to light at all. In addition, if I revisit any of these
adjustments a few hours or days later, I find that most are once again
out of calibration.
*Oscillator drift test: I ran this test several times, and each time it
passed without issue.
*Auto Tune does not indicate problems with any of the voices.

I've also noticed that at some point one of the bridge rectifiers for
the power supply must have let go, as one of them has clearly been
replaced, and there is a bit of damage on the board in that area. I'm
tempted to replace the three of them just for good measure, but since
all my voltages are in spec at I and J, I don't think they are the
source of my problems. Or could they be At any rate, given this
information, does anyone have suggestions as to where to go from here
Any feedback would be greatly appreciated.

Thanks,

george