Trouble with Control Board Audio Output

Bad board is possible. Single board often serves many panels and if they wired something wrong... (Not you, the manufacturer). 

@marcdraco Probably didn't make myself clear--I've built two other monitors with two other, separate control boards of different models, and they both had the same problem.

I’ve done a couple myself. One of them wouldn’t even fire up the display despite being “guaranteed” for that panel. 

Is this the only one causing issues? 

@marcdraco No, all of my control boards do this. I have one powering a laptop screen, one powering an LCD panel from an old iMac, and now this one, which I'm using to repair an Asus PB278Q. I've never gotten an audio output out of any of these. The audio ports seem securely seated on the circuit boards as well. They're also all from different sellers (so I assume from different manufacturers), and I bought them with at least 6 months' time between each purchase, which is why I don't think it's a production line fault. 

I use HDMI and Displayport for all of them, and they're all being powered by an RTX 3080 Ti, if that helps.

OK, have you looked at your software audio mixer to make sure the nVidia audio drivers are there? I'm not sure if the video card has its own audio but I've seen them listed on machines with other cards like the 1080 and my 4060.

If the drivers are missing -or- IIRC, if the software mixer isn't pointing to that output, you won't get sound over HDMI. 

I find it sometimes helps to use a live Linux (something like Ubuntu, Mint, etc.) to see if I can see any life in the devices.

However, I would probably try to validate that sound is coming from HDMI in the first place by popping it into your nearest HDMI-capable TV - which should be any modern device.

@marcdraco Okay so an update: one of my DIY monitor's sound outputs does actually work for some reason. It's not the one I'm currently working on, but it does make me think that it is unlikely that it's the GPU's fault. I have a funny feeling now that it might have worked once before, but that I'd just forgotten it, and this just makes me more confused.

I'm pretty sure I have all the audio drivers. I use the NVIDIA app to download my drivers, and I get the studio bundle every time. Also, when I plug in my DIY monitors, their names appear in the sound outputs, I just never hear any sound when I select them--except, apparently, for the one that started working. I also unfortunately don't have any normal monitors or TVs with built-in speakers, so I can't test that way either.

Seeing as I'm upgrading my PC in a few days anyway, I think I'll wait until then to continue troubleshooting. If it's a PC hardware issue, there's not much point in finding out the problem, only to switch to a different machine anyway. Thanks for your help!