Comment 3 for bug 200523

The MCP51 mixer gets muted unless you specify correct model option.

The file /usr/share/doc/alsa-base/driver/ALSA-configuration.txt.gz lists different options for driver snd-hda-intel. For instance, my mobo is ASUS M2NPV-VM, and model alsa-dig seems to work on it.

You can try different model names until you get mixer unmuted.

Remove snd-hda-intel module and reinstall it with correct "model", e.g.,

sudo rmmod snd_hda_intel
sudo modprobe snd_hda_intel model=alsa-dig

If the module is in use, see which process keeps it open with

sudo lsof /dev/snd/*

and kill the processes.

As permanent fix, add line with correct module option to /etc/modprobe.d/options:

options snd-hda-intel model=alsa-dig

Also, make sure that you don't already have an incorrect options line.