There's no firmware update for the M8892/A1025 (the 1GHz Ti Powerbook).
Pulled the logic board - cables all seemed intact and attached. Put it all back together again - still only mono sound - and now only coming through the headphone jack. I've read that this can be a sticking jack, as only headphone is selectable in OSX's sound control panel. Wriggling the headphone plug didn't resolve it. The fact it's only mono through the headphone, as well as the external speaker, leads me to suspect a soundboard i.e. logic board problem, rather than a loose or blown speaker, no?
Pulled the logic board - cables all seemed intact and attached. Put it all back together again - still only mono sound - and now only coming through the headphone jack. I've read that this can be a sticking jack, as only headphone is selectable in OSX's sound control panel. Wriggling the headphone plug didn't resolve it. The fact it's only mono through the headphone, as well as the external speaker, leads me to suspect a soundboard i.e. logic board problem, rather than a loose or blown speaker, no?