I would start (surprisingly) with checking LFO circuit :-)
Look if there's no cable broken or connector disconnected. Clean all connectors and reseat them. Reseat carefully all IC's in sockets. Check if switches work properly.
If this doesn't help, it needs more detailed analysis of signals with oscilloscope.
There's also lot of trimmers for calibration, maybe your instrument needs such calibration.
Let me know if you need Service manual, I have some downloaded from internet. There's description how to calibrate LFO's.
Good luck with repair. Probably it will be not so difficult.
Daniel Forro
On 27 Jun, 2014, at 8:35 PM,
zap@...
[oberheim] wrote:
Hi guys,
first time post to this group, so hello to all of you. I recently bought a used OB-Xa for a quite reasonable price and face the following
problem:
All controls on the surface work fine except the LFO Rate. The depth controls for Pitch/Filter and PWM, however show a change to the destination, but in a static way. The LFO isn't oscillating.
Can someone give me a hint of what could be wrong, or where to start investigating
Cheers,
Stephan