I did some Google searching in various forums and Sony Vaio sound problems
go back as far as Gutsy. There are various fixes that have been tried and
some have worked for some and not for others.

http://ubuntuforums.org/showthread.php?t=677746
www.geoffcorey.com/setup-sony-vaio-laptop-internal-microphone-ubuntu-9-10\
-vpccw17fx/

This probably isn't it, but it's worth checking...

Under Volume Control, the microphone is probably muted by default.

Problem solved, here is how i manage to make the mic works, in case it
helps somebody :
add to /etc/modprobe.d/alsa-base.conf the line
options snd-hda-intel model=auto
if it already exists, just change the value into : auto
after that configure the input levels : choose mic and not front mic as
an input device.
reboot your computer and cross your fingers!