Z-Axis Stepper only moving downwards

[mighty 0]

Hallo everyone,

I hope someone can help me with my stepper problem.

My Ultimaker was running perfect for about 3-4 month.

Now my Z-Axis stepper is only moving the platform downwards.

If I manually move the axis with my Ulticontroller, the platform lowers always (turn clockwise and counterclockwise).

(the same result by PC-USB controlling)

What I´ve done so far:

- change stepper driver with another axis (same problem with the Z-Axis)

- flashed Firmware many times

- inverted the axis in the firmware

- checked the endstops (the endstops are working correctly)

- checked the cable connections

Thanx for help

Mighty