Comment 7 for bug 546769

I've had the same problem on Lucid. I've found a solution in Bug report #445889. I will quote Arwin Tugade:
"
There is this tool that lets you flip settings around but the changes aren't persistant: http://www.alsa-project.org/main/index.php/HDA_Analyzer

To get my speakers working, I ran the hda_analyzer above and under "Node[0x19]" at the bottom in a pane called "Widget Control", I flipped the VREF to "HIZ" and that did the trick. Because I'm impatient, I flipped this value in the kernel source tree I'm using (stable 2.6.33.2):

<KERNPATH>/sound/pci/hda/patch_realtek.c

13479c13479
< {0x19, AC_VERB_SET_PIN_WIDGET_CONTROL, PIN_VREF80},
---
> {0x19, AC_VERB_SET_PIN_WIDGET_CONTROL, PIN_IN},

Recompiled and it's persistent. This is just informational and is by no means a official solution, so use it at your own risk, I just wanted to get this out of the way so I can get on to using my laptop. "

I haven't changed the value in the kernel source yet. But the non-persistent solution works for me so the persistent solution should work to. But it's quite harder...