My HDMI sound is connected from an intel NUC core i3 (a version without all the extra legacy serial and vga interfaces) and connected to a 1080p ViewSonic Monitor with built in speakers. My sound mysteriously failed again, after having worked just fine for a couple of months. (this is a repeating issue) This has happened several times before. Sometimes a shutdown and restart restores the sound after a few tries, other times it takes many days, then a shutdown/restart immediately restores the sound. In all the other cases of HDMI sound failure to my Viewsonic Monitor, the sound (if it inexplicably resolves) will occur immediately after a restart, and without prior settings readjustment. And, in every case the sound was originally working just fine, up until the Intel NUC was powered off for whatever reason reason.
I've checked all the normal things like mute buttons, sound settings, but adjusting those never helps. The settings are correct because they were working beforehand.
This has happened with numerous Linux operating systems. Right now I'm using Kubuntu 14.04. ...then eventually, sometimes days later but immediately after a restart, the sound starts working again, inexplicably. Any ideas what's going on? (I'm the only one who uses this computer)
I don't believe it's a hardware issue because when the sound does work, it works perfectly, and when the sound fails, it fails completely, and both the sound-failure and the sound-fix are somehow triggered by Restarting the system, so I believe it's not a mechanical issue with the sound.
I just tested the HDMI cable and my monitor (Viewsonic 1080p with built in speakers) using a Raspberry Pi 2 running Ubuntu Mate. The sound works fine. Next I will test both the Pi2 and my Intel NUC on a Big TV, to see what works, and what doesn't...
...testing complete. I've found the solution that worked this time, and am posting it for posterity, and to others facing the problem of their HDMI sound mysteriously going out after powering their Intel NUC off.