analog Servo spins on its own when connected to 7i77

I've got a lathe with two axes, X and Z as usual.
The Z axis is already set and works. there is a pulley between servo and leadscrew.
I did remove the pulley on the X axis since the servo starts spinning right away when drives are enabled.
Not at max speed but rather fast.

the exact same servo system on the Z axis works good, no drift no random spinning. I did already swap the drivers to no effect.

the Servo does spin when I connect the analog-+10 pin plug to the 7i77. when its not connected its not moving at all.

Linuxcnc is setup to have two axes with two encoders. when inplug in the analog plug into another analog drive header its the same effect. I didn't try to plug x into the z header.

any ideas why the servo spins up when analog plug is plugged into the 7i77 ?

Sounds like you are describing a run away servo system. First thing to check is if the encoder feedback direction is correct. Make sure that spinning the motor in the positive direction moves the DRO in the positive direction.. Second need to check if the analog output signal polarity is correct. Make sure applying a positive voltage to the drive input turns the motor in a positive direction. Both of these issues can be corrected in software by making their scale values negative (neg. encoder scale or input scale and neg. output scale). Either of the above conditions can cause a runaway as you describe. However changing both at the same time will cancel each other out and leave you with the same problem.
other out

You are correct but in my case the servo isn't connected to the axis, and only spins when the +-10V are connected to the 7i77, if unplugged the servo is perfectly still.
The exact same setup for the Z axis works.
I'll check the axis configuration today, maybe I made a mistake.

Look at the command output signals from hal. Are they zero before you "plug in" the servo? If they are zero, is the voltage at the analog out pins zero? Double check your wiring?

Does the servo spin when LinuxCNC is not running?

I have the servo enabled pins setup, so when Linux is not running, the drives are disabled. But as far as I can remember, the servo was always spinning when i turned the mains on. I just recently found out, it would stop spinning when i disconnect the +-10 plug from the 7i77.

I would:

1. Disconnect the drive from the 7I77 analog output (with all power off)

2. Power up the 7I77 with LinuxCNC not running

3. Check the analog output voltage of the affected channel
If  it is not near 0V, the 7I77 output has been damaged

If it is near 0V when LinuxCNC is not running, (this is the expected condition) 
It may simply be that the  feedback is reversed or there is some other tuning/setup
issue causing lack of control

UPDATE

okay, I'm feeling ashamed and stupid.

so the servo drives have 5 potentiometers at their front for several adjustments. guess you already know where this is going...

offset 1 and 2
rpm
P as of PID
and current

i already tried to adjust the offsets with zero effect days ago.

turns out you have to turn the potis like 8 times to get an effect from 60% to 0% offset, you can go both directions so like 20 turns at max. in fact I wasn't adjusting hard enough to get an effect.

and to my defense i bought the machines with minor problems and didn't touch the drives before and x-axis was always spinning like crazy, right from the very first start it ran into hardware endstops.

so it was just a drive someone messed with, before I got it, to get the machine running again.

no more spinning on its own. thanks.

Ahh someone was probably trying to fix a problem in the previous control
by adjusting the drive zero.