[R128 PPC] Apple Cinema Display black screen but no error

[Flachy Joe]

Hello,
I try to use a Gentoo distrib on an Apple Cube G4 and a 22" Cinema 
Display (ADC plugged).
The graphic card is an ATI Rage 128 PF/Pro AGP 4x TMDS.
First the right resolution isn't autodetected but set it manualy to 
Xorg.conf is ok. (1600x1024 at 60Hz)
Then, when I start the X server, I have a black screen, the monitor seam 
to sleep. Xorg report no error, it's just like all is good for it.

Ideas ?

Thanks.
Florian

PS: I'm french, so my english can be ...
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