Comment 2 for bug 576160

I have a Dell M1730 laptop which I believe matches with this hardware

Codec: SigmaTel STAC9228
Address: 0
Function Id: 0x1
Vendor Id: 0x83847616
Subsystem Id: 0x102801f7
Revision Id: 0x100201
No Modem Function Group found

I got the microphone to work by adding the following line to /etc/modprobe.d/alsa-base.conf

options snd-hda-intel model=dell-bios

This changed the sound preferences to have three options Microphone 1, Microphone 2 or Microphone 3.

Microphone 1 worked with skype and you can see the meter change when noise / voices are detected.

It would be nice if this worked without this mod ;) but at least there is now some info on how to get it working.