I just installed a PowerBook G4 15inch and had a similar issue. I had to insert the snd-powermac module by hand (i.e., with 'modeprobe snd- powermac') which resolved the problem on my end.
-- No Sound on Edgy PPC on Powerbook G4 17 (alsa? snd-aoa?) https://launchpad.net/bugs/64247 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
