The internal microphone suddenly stopped working in Ubuntu 18.04 on my Lenovo Yoga 900 laptop. It was working for a while before so I suspect some update caused it to stop working.
The internal microphone is detected, but simply picks up no sound (note the input level in this screenshot). I have tried an external microphone and it successfully picks up sound.
My alsa info can be found here.
snd_hda_inteldevice... I found this page a good jumping-off point. https://www.alsa-project.org/main/index.php/Help_To_Debug_Intel_HDA - although in the end, I did have to write a kernel patch to get it fixed.... the HDA codec graphing tool was a great start point. My problem was in the "patch panel" code - the stuff that determines which virtual "wires" are connected. – Adrian Sep 27 '18 at 14:21