Lucid Tips

Last month when Ubuntu 8.04 LTS (Hardy Heron) was officially release I wrote about my experience of running Ubuntu Hardy Heron on Compaq Evo N610c laptop. In response to this reader Graham posted a comment indicating problem with adjusting the screen resolution to anything other than the native 1400×1050.

Since I generally use the laptop with a port replicator and external monitor I had not noticed this bug. Graham reported this bug to the Ubuntu development community and a solution was posted there that works perfectly.

Some background information - Compaq Evo N610c uses ATI Radeon Mobility 7500 display adapter. As per the responses to Graham’s posting the support by open source ATI drivers is incomplete. The actual solution is provided by Bryce Harrington who writes that Mobility 7500 uses DDC (Display Data Channel) instead of EDID (Extended Display Identification Data) and DDC is returning only one resolution. So how do you fix this? You need to manually edit the xorg.conf file and add the “NoDDC” option.

Disclaimer: These steps have worked for me and have been tested on Compaq Evo N610c running Ubuntu 8.04 LTS (Hardy Heron). YMMV. I am not responsible for loss of data or damage to computers.

Prior to making any changes check if you are able to change the screen resolution. System->Preferences->Screen Resolution. If you are able to change the resolution then these steps do not apply.

Below are the detailed steps to fix the resolution issue.

1. Open terminal
2. Navigate to /etc/X11 directory

   cd /etc/X11

3. Make a backup of existing xorg.conf file

   sudo cp xorg.conf xorg.conf.original

4. Edit the xorg.conf file

   sudo vi xorg.conf

   or if you are not comfortable use vi use gedit

   sudo gedit xorg.conf

5. Find the section that describes your Video Device. In my case it looks like

   Section "Device"
   Identifier    "Configured Video Device"
   Option        "UseFBDev"        "true"
   EndSection

6. Add the following text

   Option        "NoDDC"             "true"

7. The edited section should look similar to

   Section "Device"
   Identifier    "Configured Video Device"
   Option        "UseFBDev"        "true"
   Option        "NoDDC"           "true"
   EndSection

8. Save the file
9. Either reboot the system or restart XWindow (ctrl+alt+backspace) for the changes to take effect.

You should now be able to change screen resolution.

For reference here’s my xorg.conf file. On a side note OpenSUSE 10.3 on the same Compaq Evo N610c allows adjusting screen resolution without any changes to xorg.conf file (OpenSUSE 10.3 xorg.conf file). The above fix seems to work on FreeBSD too although I have not tested it myself.