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EnglishMohican

Member

Registered: 2022-09-15

Posts: 20  

[SOLVED] Only top half of screen works while in Grub

I have been running Excalibur on my laptop for over a year. I do have two Excalibur installations in separate partitions, one an upgrade from a used Daedalus and the other an upgrade from a fresh install of Daedalus. Both worked fine until recently. There is also a Windows partition. The laptop has both an AMD integrated gpu and a separate Nvidia GPU.

A possible cause of my problem is that I installed and ran Plymouth and the problem occurred soon after, though not immediately.

So the problem is that when I turn on my laptop, only the top half of the screen is active. There is a band of broken up lines half way down the screen and below that the bottom half of the of the screen is inactive. Only the top half scrolls.  OS selection is possible as that is in the top half of the screen but the log-in box is a problem as that is under the broken up band of lines. Once I succeed in logging in, the screen instantly changes to a perfectly normal full screen that works well until I log out  - at which point the screen sometimes returns to the half screen active version (with a log-in box hiding behind the broken lines. When I log back in, the screen starts operating properly again.

I have been trying to read up on this. As I understand it, the screen is initially set up by the EFI BIOS and then grub takes over. Some reports say that Grub just uses whatever screen it finds as is without changing it but others imply that grub can select a screen resolution, colour etc. Grub handles selection of an OS and then hands control over to the init procedure of the selected OS which puts up the log-in screen. Initially, I blamed grub for not setting the screen correctly and thought that it was the OS taking control that corrected the screen - but the log-in screen is surely set up by the OS after (in my case) lightdm has taken charge.

I believe that grub uses the EFI graphics driver as the two built in ones seem totally irrelevant, Cirrus and something else I do not have. I have tried various "repairs", uninstalled Plymouth, tried various settings in grub etc but nothing has made much difference.

Does anybody have experience of this sort of problem or can anybody comment on when the OS positively takes charge of the screen?

stargate-sg1-cheyenne-mtn

Member

Registered: 2023-11-27

Posts: 472  

Re: [SOLVED] Only top half of screen works while in Grub

what happens when you use a liveusb?

this was one of the results from searching DDG-Lite for "grub only the top half of the screen is active"(no quotations)

https://elementaryos.stackexchange.com/questions/25485/live-usb-only-displays-on-half-the-screen-installation-fails

keep us posted on your progress!

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EnglishMohican

Member

Registered: 2022-09-15

Posts: 20  

Re: [SOLVED] Only top half of screen works while in Grub

Just to  finish this thread,

I believe the TCON within the screen has failed. The screen works well in 60Hz mode but not in 144Hz mode. The initial start-up reset puts it into 144Hz mode, so the UEFI (firmware) screen also only shows the top half. Although the web says I should be able to get GRUB to switch into 60Hz operation when it starts, nothing that I have tried seems to achieve that.

Once I select an OS and get into it, I  can use X to set up 60Hz and I have a full screen again. If I try to switch back to 144Hz, I am back to half a screen.

An external screen (admittedly running at 60Hz) shows a full screen even when the laptop is set to 144Hz for its screen and only showing a part picture. So the GPU is working and putting a valid picture into the framebuffer. The problem is on the output side of the framebuffer which is almost entirely the TCON built into the screen itself.

So basically a hardware failure but with a few puzzles left (to be ignored)  about why the various GRUB configuration methods seem not to work.

fsmithred

Administrator

Registered: 2016-11-25

Posts: 2,800  

Re: [SOLVED] Only top half of screen works while in Grub

I see something like this on one laptop that's fixed by changing the screen resolution for grub.
Edit /etc/default/grub to uncomment this line: #GRUB_GFXMODE=640x480 and change the resolution, then run update-grub and reboot. You might need to try a few resolutions until you find one that works.