Bigbad,
I have the same issue. My music is fine, but no sound effects or speech.
I'm told that something is wrong with the CPU board. I have minor alkaline corrosion but it is limited to only 10 or so components and all adjacent traces appear to have 0 ohms, I am lucky.
Possibly it's an EPROM, but I suspect discrete components instead.
I'm having my board inspected today, perhaps I can let you know what problems need to be fixed on my board.
Tim