Fanuc 0T C positioning

[richardfp4]

We have a Takisawa TC3 and just bought a Victor
Vturn 20 with both a 1990 0TC. They both have the
same Fanuc 5.9 NM servo motor and the weight of the
turrets are comparable. There is no friction or any other
mechanical problem, they both have very few backlash in
the spindles or guides. The machines are both in very
good mechanical state.

The Takisawa is much stiffer on the X controll loop
and is much faster when positioning a couple of hundreds
of a mm. It moves instantly with the handle.

The Victor is less stiff and slow when for example
moving a couple of hundreds of a mm on the handwheel.
After the position is done, you sometimes see that
it moves a little more again after half second or so.
I checked and optimized the backlash compensation
(parameter 535) on the X-ax and it is only 0.011 mm
which is good.

I have the impression that the position loop gain is
too low or it could also be that there is some integral
gain that is not wright. We have some experience with
adjusting PID filters on servo systems but I cannot find
anything usefull in the manual. I only found a 8000 parameter
that adjust the inertia ratio between the servo motor and
the driven parts but I wonder if that could be the cause.
I also found a general proportional gain parameter, but
as it is only the X-ax I think it is tricky to change that.

I have red the fanuc service manual but I could not find
anything to start with. I think it is has something to
do with the positioning loop filter.
Is there a kind of service manual for adjusting the servo
loop? I hope someone can help me a little bit.

Thanks for your help
Richard