13 AMD 7640U / Kubuntu - External monitor not working

Hi all,

I have a AMD Ryzen 5 7640U, and have just installed Kubuntu (dual booting with windows 11).
I have both Display Port and HDMI expansion cards (I’d prefer to use display port if possible).
I have a Samsung G9 monitor which runs at 5120x1440 resolution natively.

On the first ever boot of Kubuntu I was able to get the monitor working by enabling it and setting the resolution to 1024x768, this worked, i then upped the resolution gradually until getting to 5120x1440.
After a reboot however, the monitor is disabled and no combination of lower resolution will output to the monitor.
I updated (apt update) rebooted and now every time i attempt to enable the monitor and hit apply I get a hard crash.

Does anyone have any experience with this or a similar setup or does anyone have any recommendations of things I could try? I use my laptop primarily at my desk with my monitor so I really like to get this working.

I just tried HDMI, can’t get it to go past 640x480 resolution and the picture looks garbled, not sure how to describe it.

I switched the back to display port, but this time connected the expansion card to the rear right slot which seems to be working perfectly however, if I’m not mistaken it’s recommended to charge/USB-C in this slot right?

Under linux, just check what the system detects with xrandr - it will show you all possible resolutions with frequencies. (Note - you have to start it inside a console → try konsole).

But, checking the AMD specs of the CPU, especially GPU (https://www.amd.com/en/product/13196) it seems the 5120x1440 is not supported. But I wouldn’t bet on these.
Check the output of the xrandr call and you’ll know what has been detected and should work.

Note also that on these high frequencies, you need to have a decent cable attached (HDMI or DP).