Help. x1600, dual monitors, DVI twitching

Alex Deucher alexdeucher at
Wed Aug 5 13:10:15 PDT 2009

On Wed, Aug 5, 2009 at 3:24 PM, Ron King<rking at> wrote:
> Hi,
> I'm on Fedora 11, M56 x1600, X server 1.6.2-3, ATI driver 6.12.2-14.
> Laptop with docking station and dual Samsung SyncMaster 940Be LCDs.
> Docking station has one VGA and one DVI-D.  All works fine in XP, Fedora
> 8 (using Xrandr 1.2, I believe).
> LVDS and VGA work fine, alone or dual.  DVI produces a vertical twitch,
> always.  Running the cursor up the screen shows missing horizontal
> lines.  Modes appear to be correct and match published monitor modes.
> Changing modelines with xorg.conf and Xrandr do not seem to have any
> effects.  Adding modes in Xrandr and using them causes the monitor to
> blank, then return and still report the same problem.   Monitor reports
> 31.7kHz and 30Hz regardless of changes.  Is this mode hard coded for
> DVI-D somewhere?

It sounds like your monitor doesn't like dvi coherent mode.  try:
xrandr --output DVI-0 --set coherent_mode 0
xrandr --output DVI-0 --off
xrandr --output DVI-0 --auto
If that doesn't work, you might try the driver from xf86-video-ati git
master.  The display issues may be due to underflow to the display


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