ATI 9250: screen black for a second

[Hartmut Niemann]

Hello!

I have a 
  01:00.0 VGA compatible controller: ATI Technologies Inc RV280 [Radeon 9200 SE] (rev 01)
ATI 9250 card on a BENQ G2400W, connected with DVI,
The software is debian testing with 
	Kernel 2.6.30

	X.Org X Server 1.7.7
	Release Date: 2010-05-04

(II) Module radeon: vendor="X.Org Foundation"
        compiled for 1.7.7, module version = 6.13.0

and during normal X work (KDE 4.3.4) the screen often goes black for a second or so,
like someone needs to resync for whatever reason.
This happens maybe every 5 minutes.

What can that be? What can I do against it?

With best regards
Hartmut Niemann