Comment 13 for bug 534372

I had the same problem in Ubuntu Lucid on a Sony VAIO VPCEB1M1E.

I've run hda-analyzer, and under Node[0x19] PIN, changed Widget Control VREF from 80 to HIZ. Problem solved, sound restored.

However, running hda-analyzer and clicking through that every time is somewhat laborious, so I've downloaded the hda-verb utility, compiled it, and added a script to rc.local to invoke it this way:

/PATH/TO/hda-verb /dev/snd/hwC0D0 0x19 SET_PIN_WIDGET_CONTROL 0x60

0x60 is the code for the constant VREF_HIZ.