Z Axis Jump Issue

Hello All
I have a MendelMax 1.5 from 3Dprintertek.com.
Here is the issue. It will be printing away just fine and then randomly the Z axis will just jump up 2 to 5mm and print in the air.
For example it printed up to 5mm then is will move up to the next layer but it will move up 3mm and start printing in air.

It will do this with any file that I have tried.
I have sent one of my slic3 files to 3dprintertek and they printed it just fine.
So I sure that it is not the slic3 file (at least I think so).

Things that I have done.
1. Ground all the aluminum extrusions, Y axis aluminum bed parts and connected the power supply 5V negative to ground. All this help the display from get messed up but not the Z Axis jump issue.
2. Replaced the Arduino 2560 with a different one load with Marlin 1.0. This was the fix I though but then it did it again.

Any thoughs?
It was late last night when posted this and I forgot the photo.

And thanks for all replies!

GeckospotNixie

Edited 1 time(s). Last edit at 12/01/2013 07:31AM by GeckospotNixie.

Watch the motors as the printer does the move. It will take some time to move 5mm. Either the mechanical part of the printer is shifting or the electronics are going nuts. If it's the mechanical part, you won't see the motors running for a long time. If it's the electronics then the motors will run overly long. One *very* easy way for the Z axis to jump is for the nuts on the 5mm thread rod to jump in their mounts. That's happened to me multiple times.

... don't forget a ground wire to the X and Y carriage ... (It will do nothing at all for your Z problem, but it's one more place for static to hit). The easy place to attach them is on a motor mount screw.