Atik383LC+ strange flat artefacts

[Andreas_Roerig]

Hello,

I recently bought an Atik 383LC+ and this is my first post here.
Unfortunately the camera produces some strange artefacts when taking flat frames.
It seems that I have run into the same problem that Guenther described in this older thread:

http://www.atik-cameras.com/forum/index.php?topic=122.0

The artefacts I am seeing look quite the same. It is a pattern of streams at the top of the image.
Beside this one may notice a strong color gradient from top to bottom that causes an inverted gradient in the calibrated images
I have uploaded a debayered and extremely stretched version of my masterflat here:

http://www.andreasroerig.de/test/DB_flat_stretched.jpg

The image was resized to 25 percent and saved as JPG just to show the problem.
The original masterflat can be found here:

http://www.andreasroerig.de/test/flat.fit

It is a combination of 10 single flats. Exposure was 6 seconds each. Matching darks have been subtracted.
This was taken on a 120mm refractor using EL foil with several layers of paper as light source.
Taking flats with this setup never caused any problems with my Sbig ST10 XME or my Canon DSLR.
However to rule out the optics and the foil I also tested with a canon lens instead of the refractor and tried a white illuminated wall instead of the foil.
I also rotated the foil and the camera.
Additionally I have tried two different USB cables, the Atik software as well as MaximDL and two different power supplies.
The result always remains the same.

Has anybody, especially the Atik staff, any clues?

Best regards
Andreas Rörig