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Problem

I've connected my new LG TV 55QNED823RE to my computer (Ubuntu 22.04) and unfortunately after booting up (including unlocking the disk with FDD - this part appears just fine), I end up on the login screen which is mostly black apart from few green spots in the middle.

What I checked

I tried to boot up live disks of Kali and an old Ubuntu 16.04. Both worked flawlessly. Because of this as well as the fact that the Grub menu and Luks form for the input of the disk encryption passphrase appear fine even on the main system, I think it's safe to conclude that there is no issue with the TV or the HDMI cable used for the connection.

What I think is happening

When the PC was previously connected to a Philips TV, the colours were off, and I had to change the colour profile to make it look right. Before settling on an unconventional BruceRGB profile that fit the bill, I remember going through a couple of others and sRGB was the one which gave me the terrible result similar to what I'm seeing now. Therefore, my guess is that the problem is due to the colour profile that Ubuntu decided to apply by default on the newly connected display.

What I tried

  • I attempted to switch to the terminal using Ctrl+Alt+F3 and use an existing answer to set the color profile from within the terminal using colormgr. Unfortunately, that is not possible. After Ctrl+Alt+F3 all I get is a completely black screen, that is even without the green spots. This tells me that it switched to the terminal but I cannot see any input and most of all output.
  • Using live Kali, I unlocked the disk and looked at the /var/lib/gdm3/.local/share/icc/ folder. I see that there is a new edid-*.icc file created and its content mentions my TV. Unfortunately, I didn't get any other useful info from that file.

Diagnostics

inxi -G:

Graphics:
  Device-1: Intel Atom/Celeron/Pentium Processor x5-E8000/J3xxx/N3xxx Integrated Graphics driver: i915 v: kernel
  Display: server: X.org v: 1.21.1.4 with: Xwayland v: 22.1.1 driver: X:
    loaded: modesetting unloaded: fbdev,vesa gpu: i915 tty: 91x55 resolution: 3840x2160

Additional notes

  • The machine is an 8 years old Intel NUC (model NUC5PPYH) with integrated graphics card.
  • The system has a SSH deamon running so if I plug the computer to the router I might be able to SSH into it (once I get a long enough cable so that I can connect the computer to the display and to the router at the same time).
  • I have currently no other display at my disposal, spare the option that I buy one which is not something I want to do (at least not until I get desperate). That means that a solution of connecting two displays (hopefully the other one working) and setting the right profile on the TV is currently not possible.

Progress updates

  1. I've managed to SSH into the computer while having it connected to the TV. Using colormgr I set a different colour profile ("X11 Colors") and voila, the login screen now appears. Unfortunately, after login I'm at square one: all I see is a completely black screen.
  2. After login I can switch to the terminal (Ctrl+Alt+F3) and surprisingly when I return to the GUI (Ctrl+Alt+F2), all is displayed just fine. So the remaining problem is to figure out why I get a black screen just after login.
  3. Lowering the resolution (from 4k to full HD) might have solved the remaining problem. Though, the jury is still out.
  4. Unfortunately, there are still issues. When switching users, the screen sometimes goes all red and it's not possible to switch to the console.
tmt
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