I found the solution : the "headphone jack sense" must be activated in the gnome-volume-control (accessible in the notify area). Once the option is activated, the headphones are well detected.
Users of the nforce3 chips appear to have this kind of problem. -- Speakers not muted when headphones are plugged in https://launchpad.net/bugs/37055 -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
