Well i was close… the LC475 / Q605 does not have a -12 volt rail…  It has a -5v rail…   and if that goes out you get no sound and maybe other stuff as well ( serial ports )

And as elfin mentioned before, He had situations where the metal in his LC power connector was rotted away.  That can also be bad, looks like -5v is on the end right near C129, so i bet if cap go made it to that terminal, could get rotted out. Killing your -5v rail as well.