Monitor only works if second monitor is also connected

[John6942]

Just got a GMKtek Nucbox G3 mini-PC with an N100 CPU, UHD 730 graphics, and dual HDMI outputs. It came with Windows 11 Pro pre-installed, but problem also occurs with clean Win 11 24H2 install.

This PC has an odd graphics problem that I've never seen before: One of my monitors only works when a second monitor is also connected.

Monitor 1: Vizio 4K TV
Monitor 2: HP 24" LCD monitor (from old desktop computer)

The LCD monitor works by itself, and the TV and LCD monitor work if both are connected.

But if only the TV is connected, it acts as if there is no signal from the PC. Hard to say if there really is no signal, or if the HDMI output is in a format the TV can't process -- I don't have an oscilloscope or HDMI bus analyzer to check it.

The TV works by itself during UEFI boot, with the basic VGA driver in Windows 11. But it fails as soon as Windows Update installs the Intel UHD drivers.

It doesn't matter which HDMI ports are used, or which cables (I've tried all combinations).

Does this sound familiar to anybody?

[n_scott_pearson · Accepted solution]

This doesn't strike me as being a driver problem. Have you tried accessing BIOS Setup with only the TV connected? If this doesn't work (either), then it's definitely a hardware/firmware problem.
In either case, I suggest you contact the manufacturer. Don't be surprised, however, if there's nothing they can do about it.
Sorry,
...S

[John6942]

Have you tried accessing BIOS Setup with only the TV connected?

Yes. UEFI setup works OK. TV also works by itself with Ubuntu 24 Linux. Only fails once UHD drivers get installed on Windows 11.

... I suggest you contact the manufacturer. Don't be surprised, however, if there's nothing they can do about it.

My only real hope was that somebody might recognize the problem. I don't expect the vendor to be able to troubleshoot or fix it.

Looks like I'll be sending this mini-PC back for a refund.

Thanks for the response.