Vintage Synth Repair

Anyone ever work on a Synthex?  I have one with a weird problem.

VCO 2 of 1 voice card is not quite in tune.  It's off by as much as 
1 and a half steps  (ie - D# when you press C), but only in the lower
ranges.  On a normal synth, you'd look at the range and scale trimmers
to bring it back in spec across the playable range, but the Synthex
doesn't have individual oscillator trims.

The problem follows the voice card and it's just 1 VCO of 1 voice, so 
it's not any of the controller cards or master oscillator.

My guess is that a component has drifted out of spec or gone bad, but
where to start?  Any suggestions from folks that have worked on the
Synthex?

thanks
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Tom Moravansky                                    tom@...