Quoted from Robotworkshop:
Can you post pictures on how the wires for the sound are plugged in? Also of the Rottendog board.
The photo dump, as promised.
Condition of old MPU after a lot of attempted cleanup, with (original?) ROMs sitting on top:
Sound board. The ROM was actually "Music / Spch" which potentially blows my theory that it was that chip, since speech works.
Rottendog 11A Audio Module:
The area below that in case it's relevant: