06-02-2013, 12:59 PM
That makes sense, old CRT monitors were notorious for either not supplying EDID information, or supplying bad EDID information.
The reason it only happens after you install Catalyst is because before you install Catalyst, you're using the generic Vesa driver, which only supports generic modes. It's the "this is guaranteed to work" driver. Once you install the proprietary driver, xorg learns of the specific modes your card can support, and thus tries to use an optimized mode. But since your monitor is giving xorg bad info, it ends up running in a mode your monitor can't actually support.
The reason you see the purple Ubuntu loading screen is because that screen is not displayed by x11, it's displayed on the framebuffer before xorg is started, via the vesafb framebuffer driver.
The reason it only happens after you install Catalyst is because before you install Catalyst, you're using the generic Vesa driver, which only supports generic modes. It's the "this is guaranteed to work" driver. Once you install the proprietary driver, xorg learns of the specific modes your card can support, and thus tries to use an optimized mode. But since your monitor is giving xorg bad info, it ends up running in a mode your monitor can't actually support.
The reason you see the purple Ubuntu loading screen is because that screen is not displayed by x11, it's displayed on the framebuffer before xorg is started, via the vesafb framebuffer driver.