Patches and discussion for Ensoniq VFX family

Hello,

I am new to this group as I just recent purchased an Ensoniq SD1 on 
eBay.  When I received it, everything worked just fine until I 
started to try the Pitchbend and Mod wheels.  Then after I tried to 
use them, when I would play the piano keys, the notes would be all 
shaky and jump to higher pitches, even after I returned the wheels to 
their basic non-effect positions.  So I turned the keyboard off.  
Then I turned it on again, and things worked just fine for several 
hours until I was done using it.

The next day, it would work fine for about 30 minutes, then without 
even touching the wheels, the notes would go all shaky again.

These keyboards are extremely difficult to find in Europe so I am 
wondering if this problem is not too expensive to repair, if it is 
even at all possible?

If anyone has any suggestions, please let me know.

Thank you very much for your time.