Comment 13 for bug 1414706

Could we check whether it's the jack detect or the signal which is at fault here?

To do that, install the alsa-tools-gui package and start hdajackretask. Select the analog codec, check "advanced override" and for pin 0x1a (Mic), change "jack detection" to "not present". After applying the change, now both the "Internal Mic" and "Mic" options should always be available. So plug your headset in and manually switch to the external mic.

What is the result now, e g:
 - recording from external mic?
 - recording silence or random buzz noise?
 - recording from internal mic although the external is selected?