z axis electrical freakout

[endgrainguy]

Every now and then, as in maybe every 100 hours of use, but very eratic, my z axis goes haywire.Especially apt to happen when machine is first turned on. Especially during jogging operations. It'll sometimes whir as if its being asked to do something it can't, and then it'll tend to produce random up/down motion in response to requests. I'll tell it to go up and it will go down. I'll tell it to go up again, and it will go up. At these times it sounds "excited", or maybe pissed off. Then, if I run a program multiple times, it might all at once, lose a whole lot of steps, like a quarter inch, after functioning flawlessly for hours, and then function flawlessly for hours again.Then the problem will go away, and not return for weeks. What should I suspect here? I have shielded cable to my stepper. Bad connections? Bad stepper motor? Bad stepper driver (Keling) ? Thanks!

[ger21]

Possibly a bad connection on the direction pin, or marginal voltage on that pin.

[RomanLini]

I'd also check the wiring to the motor itself.

If you have a bad connection on one motor phase it will make noises, wobble, etc, and if the load weight is pulling it downward then having a loss of one phase will make it rotate downward.

[kolias]

Had similar problem on my Z axis and after I grounded all the motor cables it seems to be ok now.

Also before I start any work on the machine I let the motors warm up for 1/2 hour