I've looked at the schematics (Sound and Serial - File P7 of those you gave me). The only thing that caught my eye as C16 ( .1µf) on the bottom of the board. Its parallel to the Reset Button (both to ground). So if C16 is shorted out then it would hold the reset down. It would also look like the reset button is shorted out.

Have you tried removing C16? And then test the reset button.