Nvidia mode is set to an incompatible mode, xorg.conf ignored

[Thorsten Barth]

I downloaded and installed the 12.04 beta 2 64-bit desktop edition, after installation upgraded to April 11, 2012.
I have an NVIDIA 6200 card. DVI out is connected to the HDMI input of a Samsung TV capable of Full HD resolution @60Hz non-interlaced, which worked perfectly with the same graphics card on MythBuntu 11.04 32-bit.

The problem:
When the service lightdm is started, and the screen mode is set to 1920x1080@50Hz interlaced after a second or so - the TV claims
that it cannot display this mode.

Details:
Ubuntu starts with a purple screen on 1920x1080@60Hz NI. For example fsck displays perfectly in this screen.
As I can see from Xorg.log files, the screen resolution is first set to "nvidia-auto-select" which seems to work well.
Then, after a second or so, "something" seems to switch modes once again, to the illegal mode.
Creating a new Xorg.conf using nvidia-xconfig does not improve anything. Again, first the correct mode is detected by DPMS, and set... and then after a second, the mode is changed to interlaced @50Hz.

Same results if I stop and restart the service "lightdm" from the console.

Could it be an issue with xrandr? I did not find any documentation in the Wiki about additional configuration files to configure video modes, or other software packages that change video modes after the X server has already been started, so I am stuck.

I searched the whole directory "/etc/X11" for files that contain anything noticable, nothing...

I think end users should not be confronted with this kind of stuff, newly installed system must show a picture anyhow, so I consider this a bug to be fixed in the distribution.

[Daniel Letzeisen (dtl131)]

It appears you know how to get to a terminal. I suggest trying a different DM (e.g. gdm3) to see if the issue is just with lightdm. If possible, run this command to gather the logs:
apport-collect 978937

[Thorsten Barth (barth-x)]

Thanks Dave, it seems to work right with gdm, but I changed some more things yesterday, so I want to reproduce everything this evening again.

[Thorsten Barth (barth-x)]

After doing an apt-get upgrade again this morning, the problem can be reproduced:
- with lightdm, video mode is changed to interlaced, which does not work for my TV
- with gdm, everything works perfectly
( I did not do anything more than "dpkg-reconfigure gdm" and selecting one of the display managers, then reboot)