Ball vario overhaul?

My wife and I have recently acquired a 1-26B with a
Ball 400/6 (not a new installation). It is plumbed
parallel with a Winter mech. (and T.E. probe). Since
we acquired it, the Ball indicates climb pretty much
at all times, and no amount of adjustment (red knob
on back), setting selections, etc. have made a difference.
The Winter works fine, and I can identify no problems
with the flask or plumbing.

I note there are 2 potentiometers pigtailed off the
back of the instrument, but I have no paperwork or
manual of any kind on it.

I was wondering if anyone knew where I could send it
for overhaul, and better yet, if anyone has data or
ideas I could use first to more completely troubleshoot/adjust
it in the field.

Short of that my next step would be to find someone
with a hole in their panel to take it up in their ship
for a test hop...