Re: KDE/SDDM screen resolution.

Hi, I have a pretty old machine with ATI R4850 in it using open source drivers. It runs F25, and until recently was booting fine. I have changed my old monitor to an UHD monitor, and that's where the problems started. I simply can't get screen to display anything, it seems, unless : 1. I connect old monitor. It shows Plymouth, then it is only active screen in SDDM, and then it turns off, leaving UHD display working. That last feature is I think thanks to fact that I've disabled it in System Settings -> Display and Monitor -> Display Configuration, as before it stayed on. 2. I set grub to use a theme. UHD screen is flashing through Plymouth run (trying to find correct resolution ?), then SDDM is shown, fully working. Upon login I can see KDE loading screen, and I'm back to blank screen presumably cycling through resolutions, as screen goes off, then on, then off and displays nothing. My assumption is that the monitor's preferred resolution is way more than my old machine can display, and it struggles with it. Any ideas on how to set the correct resolution for it KDE, and maybe for Plymouth ? I've tried setting modelines and resolution in xorg.conf file (/etc/X11/xorg.conf.d/00-video.conf to be precise), as well as presumably disabling EDID. It seems to have no effect. For Plymouth, I'm not too concern about it, I can live with text boot, but it was nice thing to have. I would prefer to have text based grub, rather than a themed one. Any ideas I could try ? Any specific settings for this ? As said, tried to set up modelines and specific resolution, but maybe this was not picked up properly. Thanks in advance.