Fix screen resolution in Ubuntu – ATI Radeon Mobility 7500

May 24th, 2008 | Category: howto, linux

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.

Open terminal
Navigate to /etc/X11 directory
```
cd /etc/X11
```
Make a backup of existing xorg.conf file
```
sudo cp xorg.conf xorg.conf.original
```
Edit the xorg.conf file
```
sudo vi xorg.conf
```
or if you are not comfortable use vi use gedit
```
sudo gedit xorg.conf
```

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

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

Add the following text

Option        "NoDDC"             "true"

The edited section should look similar to

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

Save the file
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.

Share and Enjoy:

5 comments

5 Comments so far

Brian July 30th, 2008 3:59 pm

Worked like a charm for me. I tried following some other fixes but they did not work. This one had my screen resolution resolved in a matter of minutes.
Compaq evo n610c recently upgraded to Hardy Xubuntu.
Ivan Dario otalvaro February 11th, 2009 8:46 am

Thanks, solved my problem had been unable to find a solution.

perfect!
Osama August 7th, 2009 10:50 pm

thanksssssssssssssssssssssss

the best tutorial ever
srikumar November 12th, 2009 1:00 am

Hi,
I have the same issue on my IBM R50 laptop which is using the Radeon Mobility 7500 card with Ubuntu 9.10 karmic. I tried to do modify xorg.conf but the xorg.conf itself is not available.
I create the file using Xorg -configure and added the line NoDDC and restarted the X server. But i am still unable to see the new resolution.

I looked into the log xorg.conf.log and observed that it is showing some logs related to DDC….

Please suggest me how to set this parameter on karmic which does not has xorg.conf file
Srikumar B November 12th, 2009 5:53 am

Hi,
I got the same problem in my IBM R50 thinkpad (contain Radeon Mobility 7500) with Ubuntu 9.10 Karmic. It seems Karmic does not use xorg.conf and i created the file using Xorg -configure then modified the xorg.conf adding the NoDDC line and then restarted the system but it still i am not able to increase the resoultion.

I still suspect, DDC is getting invokde because i observed from xorg.conf.0.log as below:

II) RADEON(0): Port0:
XRANDR name: VGA-0
Connector: VGA
CRT1: INTERNAL_DAC1
DDC reg: 0×60
(II) RADEON(0): Port1:
XRANDR name: DVI-0
Connector: DVI-D
DFP1: INTERNAL_TMDS1
DDC reg: 0×64
(II) RADEON(0): Port2:
XRANDR name: LVDS
Connector: LVDS
LCD1: INTERNAL_LVDS
DDC reg: 0×0
(II) RADEON(0): Port3:
XRANDR name: S-video
Connector: S-video
TV1: INTERNAL_DAC2
DDC reg: 0×0
(II) RADEON(0): I2C device “VGA-0:E-EDID segment register” registered at address 0×60.
(II) RADEON(0): I2C device “VGA-0:ddc2″ registered at address 0xA0.
(II) RADEON(0): Output: VGA-0, Detected Monitor Type: 0
finished output detect: 0
(II) RADEON(0): I2C device “DVI-0:E-EDID segment register” registered at address 0×60.
(II) RADEON(0): I2C device “DVI-0:ddc2″ registered at address 0xA0.
(II) RADEON(0): Output: DVI-0, Detected Monitor Type: 0
finished output detect: 1
(II) RADEON(0): Output: LVDS, Detected Monitor Type: 2
finished output detect: 2

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