Comment 10 for bug 573550

@rr

Expanding on igor's guide, the commands you want to run are the following (exactly what I did)

user@linux:~$ sudo cp /etc/default/grub /etc/default/grub-ORIG
user@linux:~$ sudo nano /etc/default/grub

Look for this:
GRUB_CMDLINE_LINUX=

And change the end to this:
"nomodeset"

Save the file with Ctrl+X (press Y to write to the file)

Now type:

user@linux:~$ ls /etc/modprobe.d/

and look for this file:
radeon-kms.conf

If it does not exist, create it:

user@linux:~$ sudo touch /etc/modprobe.d/radeon-kms.conf

Then open the file in nano:

user@linux:~$ sudo nano /etc/modprobe.d/radeon-kms.conf

Add this line:
options radeon modeset=0

Save it with Ctrl+X (press Y to write to the file)

Reboot the machine

After login connect svideo and run this:

xrandr -s 800x600
xrandr --addmode S-video 800x600
xrandr --output S-video --mode 800x600 (don't forget to set the PAL option here if you need to)