Every second column of pixels is black after changing MB

[MinisterK]

Hi.

I have recently changed the mainboard
of my R40, but the only available I could get was one without a FireWire Port and with
a Radeon Mobility M6-C16H with 16MB of video memory, instead of my former Radeon Mobility
7500 chip with 32MB.
My problem now is the following:
Every second column of pixels on my internal TFT is black, not depending on the resolution I set.
This occurs from the first moment the Notebook is switched on.
I have done a BIOS update to Version 1.27, but that changed nothing.

Is there any known possibility to solve this? Or is
the graphics chip/the mainboard incompatible with the 1400x1050 TFT in Thinkpads? (According to the chip's data sheet the resolution normally is possible).

http://home.arcor.de/derflo84/bilder/streifen.jpg
(The bending of the stripes is just a photographic effect)

Thanks in advance.

MinisterK