[RESOLVED] Suddenly only one of of two monitors working in Plasma

[ralfheinz]

Hi all,

I'm struggling with a strange dual display problem, occuring as soon as the Plasma desktop starts and disappearing immediately after telling the machine to shut down.

My setup is a 2012 MacBookPro with a second monitor on Kubuntu 22.04. The system is running since one and a half years without any significant problems, neither with the monitors nor something else. In detail:

During the whole boot process including the KDE logo popup after logging in, both monitors display the same. Immediately after the KDE logo disappears and the desktop starts, the laptop screen gets black and only the external display works. Unplugging the HDMI cable from the laptop brings back the picture to its screen, plugging it back in makes it black again. As I said above: as soon as I shut down, both displays are back in the game.

The error appeared literally overnight, I didn't even touch the computer between everything worked until it didn't anymore.

Settings/Display & Monitor obviously detects the two monitors 'Laptop Screen' and 'BenQPD2500Q', but when I click on 'Identify' I get the same result 'BenQPD2500Q' in both cases.

As both displays work in every situation outside the Plasma desktop I tend to exclude hardware damages as well as driver problems and assume the devil is hiding somewhere in Plasma. Sadly I have not the slightest idea where to start searching for him.

[ralfheinz]

oshunluvr Schwarzer Kater Since 'a simpler solution' sounds a little bit nicer than 'very little flexibility' I tried the Backports PPAs suggestion first and it worked – both monitors act like before! So thanks a lot to both of you.

Beside that, it's hard to understand what was going on here. Going to bed with a working system and waking up with a damaged one seems to be a bit too much for my average intelligence. I think I will try to distract myself from those gnawing questions by trying out mbpfan – thanks for this recommendation too!

[oshunluvr]

Which operating system are you using?

Are you using Wayland or X11?

Can you translate the warning message displayed at the top of the window?

[ralfheinz]

oshunluvr I'm using Kubuntu 22.04 (with all the latest updates delivered by discover) and X11. The warning says something like 'A new output was added. The settings were reloaded.' I think it appeared while I was clicking around for the screenshots.

[oshunluvr]

Thanks for the translation. Try running "xrandr" in Konsole and pasting the output here.

I'm going to guess that the version of Kscreen you are using is the culprit. I had to remove it in the past to avoid dual monitor problems. The solution was to create an xrandr script that set the monitors correctly and uninstall kscreen. The difficulty with doing this is you have very little flexibility if you tend to change monitors or remove the external one occasionally.

[Schwarzer Kater]

Perhaps a simpler solution could be to additionally use the Kubuntu Backports and Kubuntu Backports PPAs for Kubuntu 22.04 LTS, because then you will get Plasma 5.27.x and in Plasma 5.27.x the multi monitor support has been vastly improved compared to Plasma 5.24.x …
If interested see e.g. KDE Plasma 5.27.11 available in Kubuntu Backports Extra.

PS: This has nothing to do with the topic, but I would suggest to install mbpfan for your MacBook Pro (if you haven't already done this) so you can properly adjust the fan speeds and cooling for your laptop.

[ralfheinz]

Thanks for the translation. Try running "xrandr" in Konsole and pasting the output here.

I'm going to guess that the version of Kscreen you are using is the culprit. I had to remove it in the past to avoid dual monitor problems. The solution was to create an xrandr script that set the monitors correctly and uninstall kscreen. The difficulty with doing this is you have very little flexibility if you tend to change monitors or remove the external one occasionally.

xrandr output:

Screen 0: minimum 320 x 200, current 2560 x 1440, maximum 16384 x 16384
eDP-1 connected (normal left inverted right x axis y axis)
2880x1800 59.99 +
2880x1620 59.99
2560x1600 59.99
2560x1440 59.99
2048x1536 59.99
1920x1440 59.99
1856x1392 59.99
1792x1344 59.99
2048x1152 59.99
1920x1200 59.99
1920x1080 59.99
1600x1200 59.99
1680x1050 59.99
1400x1050 59.99
1600x900 59.99
1280x1024 59.99
1400x900 59.99
1280x960 59.99
1440x810 59.99
1368x768 59.99
1280x800 59.99
1280x720 59.99
1024x768 59.99
960x720 59.99
928x696 59.99
896x672 59.99
1024x576 59.99
960x600 59.99
960x540 59.99
800x600 59.99
840x525 59.99
864x486 59.99
700x525 59.99
800x450 59.99
640x512 59.99
700x450 59.99
640x480 59.99
720x405 59.99
684x384 59.99
640x360 59.99
512x384 59.99
512x288 59.99
480x270 59.99
400x300 59.99
432x243 59.99
320x240 59.99
360x202 59.99
320x180 59.99
DP-1 disconnected (normal left inverted right x axis y axis)
HDMI-1 disconnected (normal left inverted right x axis y axis)
DP-2 disconnected (normal left inverted right x axis y axis)
HDMI-2 disconnected (normal left inverted right x axis y axis)
HDMI-3 connected primary 2560x1440+0+0 (normal left inverted right x axis y axis) 553mm x 311mm
2560x1440 59.95*+
1920x1080 60.00 60.00 50.00 59.94 30.00 25.00 24.00 29.97 23.98
1920x1080i 60.00 50.00 59.94
1680x1050 59.88
1600x900 60.00
1280x1024 75.02 60.02
1280x800 59.91
1152x864 75.00
1280x720 60.00 50.00 59.94
1024x768 75.03 60.00
832x624 74.55
800x600 75.00 60.32
720x576 50.00
720x480 60.00 59.94
720x480i 60.00 59.94
640x480 75.00 60.00 59.94
720x400 70.08

[claydoh]

Have you looked at hardware -- even though the monitor is on during boot, perhaps it has been set to disable the screen when an external monitor is plugged in? (keyboard combos, like these?)

[ralfheinz]

oshunluvr Schwarzer Kater Since 'a simpler solution' sounds a little bit nicer than 'very little flexibility' I tried the Backports PPAs suggestion first and it worked – both monitors act like before! So thanks a lot to both of you.

Beside that, it's hard to understand what was going on here. Going to bed with a working system and waking up with a damaged one seems to be a bit too much for my average intelligence. I think I will try to distract myself from those gnawing questions by trying out mbpfan – thanks for this recommendation too!

[ralfheinz]

claydoh Thanks for your response. I saw another post (can't remember where) describing the same thing discussed in your linked post and checked that, but couldn't find any setting or combo that could have caused the problem.