Cfrgtkky

My son's PC is running XUbuntu 16.04 LTS. For years the monitor would periodically go black for a short while. I have finally got round to trying to fix it and it is not going well.

First I tried a different monitor in case the monitor is at fault. The other monitor showed exactly the same behaviour so I don't think the monitor is the problem.

Next I got an old nVidia graphics card and installed that into the PC. I installed drivers, upgraded all the packages and so on, all done remotely from my main PC. When I then went to use my son's PC, I saw the monitor was black. I tried plugging the monitor into the old onboard graphics output, not expecting much, and sure enough the screen stayed black. I then plugged the monitor into the new nVidia graphics card output and wahey, the monitor worked.

I did some more stuff and rebooted and lo and behold, the monitor was black again. I repeated the process of plugging the monitor into the old card and back into the new and the monitor started working...for a while. Five minutes later while editing xorg.conf, the screen went black again.

The PC is using lightdm.

I believe that the original behaviour was due to XUbuntu periodically losing monitor detection and then detecting it again after a few seconds.

I believe that the new behaviour is because XUbuntu is only trying to use the old on-board graphics card to detect the monitor and, as before, periodically un-detects the monitor.

"xrandr" reports two displays.

How do I get Xubuntu to completely forget about the old on-board graphics card and only use the new nVidia graphics card for display?

How do I get Xubuntu to always enable the monitor output even if detection fails from time to time.

xrandr says:

Screen 0: minimum 8 x 8, current 1280 x 1024, maximum 4096 x 4096

DVI-I-0 disconnected primary (normal left inverted right x axis y axis)

VGA-0 disconnected (normal left inverted right x axis y axis)

TV-0 disconnected (normal left inverted right x axis y axis)

DVI-I-1 connected 1280x1024+0+0 (normal left inverted right x axis y axis) 376mm x 301mm

   1280x1024     60.02*+  75.02  

   1024x768      75.03    70.07    60.00  

   800x600       75.00    72.19    60.32  

   640x480       75.00    72.81    59.94  

I have disabled the on-board graphics in the BIOS as per the comment below, but I still get this xrandr output. Where does "DVI-I-0" come from? Obviously it is from the on-board graphics card, but that has been disabled!!

The original drivers were from nVidia's website. They were causing crashes (apparently a known but never going to be fixed issue) so I uninstalled them and used the nVidia drivers from the Ubuntu repo. I no longer get crashes but I still get the black screen. It seems generally less frequent, but I did get it twice in a row. None of the logs in /var/log show anything useful as far as I can see.

I tried running xrandr with the monitor unplugged and then plugged into the old graphics card. When I plugged back into the new one I found myself on the login screen and XUbuntu was reporting an Xorg crash.

I tried just running xrandr with the monitor unplugged and couldn't get video back at all. I had to remotely reboot the computer. After it came up I tried the same thing, just running xrandr with the monitor unplugged, and again I couldn't get video back.

This is not going well. I have turned my young son's irritating video glitch into a non-operational PC problem :( Still, we have some old PCs at work we are going to throw away. I'm sure the boss won't mind me having one. They probably are much better than my son's PC too.

Someone on another forum suggested that the cable might be a problem. I have swapped the cable with that on a Windows PC and now both the Windows and the Linux PC are working fine with no problems seen (so far).

So I guess the answer was that the cable was faulty.

I ended up taking out the nVidia graphics card. With it in and everything sort of working I could get WoW WotLK working under Wine, but Steam refused to run, and the boy prefers playing Steam games so...