This is mostly a note to my future self, or to some googling Ubuntu user in a similar situation. When I upgraded my Sony Vaio PCG-TR3A laptop recently from Feisty Fawn (7.04) to Hardy Heron (8.04) with a fresh install, most things just worked with no tweaking, but sound did not. After trying some of the suggestions at the Ubuntu wiki's Debugging Sound Problems page, I fixed the sound by installing gnome-alsamixer, launching it, and de-selecting the External Amplifier switch.