For starters, enter this in the terminal
gksudo xed /usr/share/pulseaudio/alsa-mixer/paths/analog-output-headphones.conf
and when the file opens find this section:
Code: Select all
[Element Speaker+LO]
switch = off
volume = off
Code: Select all
[Element Speaker+LO]
switch = mute
volume = merge
Be aware that at first, the Line will probably be muted. You can unmute it however you wish, and it will hopefully work. The amixer toggle command should be both quick and sufficient.
If there's still no difference, do the above again and change mute to on then save, reboot and test.