This was an easy one, but just due to being so busy I never got around to investigating the issue. Basically on my JP6 for the past 2 or 3 years (basically since I moved, you'll see why!) I've had my 2 voice board go off pitch or to frequencies I couldn't hear. Thumping the bottom of the keyboard and pressing tune would solve
it temporarily. When I did have a short amount of time I opened up the top and checked connectors and sockets. That fixes the problem too.
It wasn't until yesterday that I found the problem and solved it. IC11 (an intersil chip) has an ECO on my JP that jumpers a resistor from IC12 (an op amp). Its lead
is shielded, however the solder point on the IC11 was just touching. So, it would lose contact an cause the voices on that board to go wonky. Very easy fix, just heat up the solder point.
So if you have a voice board that is going wonky, take it out and look at the underside for that ECO. It may be simple as that!