Sound: Headphones - yes, speakers - no

[Cameron Hutchison]

I have just installed Ubuntu 10.04 on a Compaq Presario CQ42-210AU
laptop. I cannot get the speakers in the laptop working. It does work if
I plug in the headphones. It is not a volume or mute issue. Pulseaudio
is set up to use the device (and clearly does when the headphones are
plugged in).

I have tried installing PPAs from ricotz to upgrade alsa to 1.0.23, as
some people had the same problem and it was solved with a later release
of alsa.

The audio device is:
00:14.2 Audio device: ATI Technologies Inc SBx00 Azalia (Intel HDA) (rev 40)

The module loaded for this card is:
  snd_hda_codec_realtek

I have read of similar sorts of issues in the past which were solved by
passing some module parameters to the appropriate alsa modules, but I
dont know what those parameters might be.

Can any one suggest something to try? (I wont be removing pulseaudio)