External 4K Monitor Unable To Run At Full Resolution Post Upgrade

[firebadger]

Hi,

After recently upgrading from Kubuntu 22.04 to 24.04 my 4K external monitor isn't working properly. When I enable it at full resolution it remains black and my computer grinds to a halt and I have to reboot. I can enable it at 1920x1080 or 2560x1440.

However if I try and change it to native resolution (3840x2160) it simply does not change.

If it is disabled and I enable it directly into that resolution, it does not show, and everything grinds to a halt.

I've experimented with different drivers but did not improve matters.

I'm currently running the "recommended" proprietary Nvidia 550 drivers. And the Nvidia card is active.

My computer is a Dell XPS 15 laptop with Nvidia RTX 305o Ti Laptop GPU.

Would love some advice. It was all working fine pre-upgrade. And I'm not keen to have to start again with a clean install.

Thanks,
Alan

[firebadger]

No idea what was wrong but is now sorted. As a random dice-throw, I installed "Monitor Settings" for LXDE and got it to set the large monitor's settings to "auto" and it worked. I assume it must have removed/reset some dodgy config.

[firebadger]

Actually it is now back the way it was. Cannot set it to 4K (60hz) no matter what I try - even repeating that last trick. It is incredibly frustrating. Delighted to hear any ideas or suggestions. 30hz now seems to work, but is far from ideal.

[jrwatts]

Sounds like you might have a bad HDMI cable. I had similar symptoms and traced it to a bad cable.

[firebadger]

Good suggestion, but was working before. However I'll try that.