I just bought a new computer with RX 5600 XT and wanted to try Manjaro on it.
However, I did have a problem installing. Booting from usb stick ended up on black screen (monitor went to standby) after a few seconds.
I managed to install in the end by using the Architect edition and adding nomodeset to boot options in grub.
Now that I have the system installed, I have the same problem. Just after boot starts, the screen turns off.
What I tried:
Setting nomodeset. This gets the system to boot, X does not work, but I can get to a different TTY and login to CLI. I did find that nomodeset disables the amdgpu driver, so this is not a solution anyway.
Installing vesa with mhwd -i pci video-vesa. This does get me to Gnome desktop, but uses vesa.
First booting normaly (I get the screen off issue), then rebooting with nomodeset and checking the logs of previous boot. This is in the logs:
I found the cause of the issue. It was a bad (old/incompetable?) displayport cable
The full story:
Following @stephane’s reply, I first wanted to check if it’s not perhaps the card’s fault before reporting this as a bug. I installed Windows 10, which went without a hitch, but then the same issue happened while installing AMD drivers. The monitor went black at the point at which the installed switches to AMD driver.
At this point I thought the card was faulty. Still I wanted to try everything I could think of before RMAing it. After some other stuff I tried the other card outputs thinking perhaps the driver switched to different one then the one my displayport cable was plugged into. I also tried connected via HDMI which supprisingly worked . This was the clued that lead my to try another displayport cable and then everything worked, both in Manjaro and Windows.