I'm trying to connect an ASUS monitor to a desktop, using an HDMI cable to an Nvidia card (GeForce GT 730). The graphics card has both HDMI and VGA ports. After connecting the HDMI cable, when HDMI input is selected on the monitor, the monitor says "No HDMI signal".

The monitor connection works perfectly using a VGA cable, so the card and monitor are good. I'm using the Noveau driver, in Debian.

xrandr gives: "HDMI-1 disconnected (normal left inverted right x axis y axis)", but the HDMI cable is connected.

Every search on this I've tried talks about connecting a second monitor to a laptop, and using Intel onboard to drive the HDMI port, which doesn't apply to my situation.

Does anybody know where to start trying to diagnose this, or how to get Nouveau to output to HDMI?

Unless the issue is with the HDMI ports on either the card or monitor. Have you examined them for dirt or damage?

Have you tried a different cable that's known to work and/or tried the cable you have on hardware that has known working ports?

Does the monitor have a source selection option that you are explicitly setting to HDMI?

Are you unplugging the VGA cable whilst trying to get the HDMI cable working?

Thanks boughtonp!

The ports look ok/clean, and I know the cable works. I did select HDMI as the source on the monitor - the monitor just pops up a box that says "No HDMI source"

Yes I've tried both booting with only HDMI cable plugged in, and also booting with VGA and then switching to HDMI. Always same result, "no HDMI source"

I bolded a piece of your post for emphasis only. Two things come to mind, having done something similar in the past. First, have you tried connecting/powering on the monitor first, before booting up? HDMI can be picky, and may not activate if it doesn't detect things in the 'right order'.

Second, I'd suggest trying the nVidia proprietary drivers. Sadly, the nouveau driver doesn't always provide 100% functionality...try the nVidia drivers, and blacklist nouveau.
https://wiki.debian.org/NvidiaGraphicsDrivers

Thanks TB0ne!

I have tried booting with the monitor powered on, no luck.

I also just installed the nvidia drivers through apt, rebooted and nvidia is now listed in lsmod, but same result: "HDMI no signal"

I noticed one difference after installing the nvidia drivers: xrandr now says that "HDMI-0 disconnected (normal left inverted right x axis y axis)" -- before it said "HDMI-1". Don't think that makes any difference, though....

Hmm; this might help. Granted, it's for Mint (and a little bit old), but may still help:
https://forums.linuxmint.com/viewtopic.php?t=235372

@pepperslq, Try booting without the HDMI cable connected and once booted connect the HDMI cable.

Which Debian is OP using? What does inxi -GSaz --vs report, ideally with at least two connected displays?

Given all OP's activity, it's not clear to me if HDMI never produces video, or if the no signal message only appears sometime after the Grub menu, or after Debian has started booting. How is xrandr output being examined? Is a second display involved, also on the 730 card? OP says he knows the cable is good, but sometimes a cable is only "good" when tried with something other than where it's needed, a form of infuriating flakiness. I've had to throw away HDMI cables several times that worked when new, but didn't last. HDMI connectors can go bad, both female and male. That's happened to me several times with various components' output connectors. Does the 730 also have a DVI connector, for 3 total outputs? If yes, try it with a DVI to HDMI converter or cable. Is OP trying to use all three 730 outputs at once? It's possible no more than two at a time can be used, and the HDMI is the one disabled when all three are connected. I have a GT 630 with HDMI, VGA & DVI outputs that with all three connected to a display produces:Note that according to xrandr, all three are "connected", but there is no resolution or location reported for the (primary) DVI port. It POSTs and puts Grub entirely on the DVI display. Shortly after making a Grub selection, the DVI goes black, and the other two light up, mirrored on the ttys, then side by side when X starts. Key to this behavior is listproviders output - "crtcs: 2" means only two outputs can function at once.

Based on info @ https://www.kernel.org/doc/Documentation/fb/modedb.txt I tried adjusting outputs using video= on Grub's linu line:This produced Xorg output on the VGA and DVI screens, but mirrored, and 1400x1050 resolution on both. Note for HDMI the name HDMI-A-1. This is the name found in /sys/class/drm/, not the xrandr name.

Then I tried adjusting with xrandr:Based on these results, I suggest it may be possible to take the same video= + xrandr approach to getting your HDMI connection to light up its display.

Just to clarify, with hdmi only can you get into your bios setup? If you are getting no output at all with hdmi only when you power on, it's definitely a hardware problem. Blown hdmi ports are not uncommon. On one of my motherboards with display port, dvi and hdmi outputs, the hdmi port stopped working one day for no apparent reason but the dvi and display ports work fine. Got a display port to hdmi adapter which I am using to this day. Just because your vga port is working doesn't mean your hdmi port is good.

Seconded.

I've had two ASUS monitors (VP278s) hanging off an nVidia card (1650) and had two devices hanging off the second monitor with both using HDMI (the second device was a Win11 laptop). Zero issues. Unfortunately, I cannot attest to what my experience might have been had I been using the Nouveau driver---that was blacklisted long ago.

OP: Unless there's some technical reason for not doing so, I'd install the nVidia driver.

1 members found this post helpful.