Vintage Synth Explorer Forums

Hey all, I'm experiencing a small, (usually tougher to figure aren't they?) but annoying problem with my OB-Xa. One voice card has a problem with VCO 1. I have moved the card around, it is certainly only on one board, one VCO, problem follows the card.

Anyway, the problem is an unsteady, and too low pitch only on VCO1. It consistently tunes significantly too low, different amounts depending on vco tune trimmer (usually between a fifth and an octave), and just has a bit of a "warble" to it. I have already tried swapping all the ICs, no luck. I've also tried recalibrating to no luck.

I was just curious if others have experienced a similar problem and may be able to give some insight before I start searching for the bad part. Thanks in advance for any help.

If you've swapped the CEM3340 on VCO 1 and you still have the problem, I would check the back of the PCB and clean off any dirt/gunk that may have built up, then turn my attention to trimmers T1, T2 & T3 and R12 (the 1M resistor from the +15 supply)

There's no other active components in that part of the circuit, and passive components rarely fail.

Good call on R12! I pulled it, and measured it, and it was conducting nothing whatsoever. Replaced it, and back to new

My OB-Xa and I thank you very much Broadwave!!

Jacob Hunt wrote:Good call on R12! I pulled it, and measured it, and it was conducting nothing whatsoever. Replaced it, and back to new

My OB-Xa and I thank you very much Broadwave!!

Always glad to help