Namco Class Of 81 Problem

[gkukuk]

Hi All, I recently picked up a Namco Class of 81 (Galaga/MsPac) in absolutely perfect condition for super cheap.  This is the smaller (home use) version with 19" monitor.  It's great because its small enough that the wife let me put it in the dining room.  Anyway, everything works great except for a few sound issues.  The woo-woo siren in Pac-man is definitely not the correct pitch, and the equivalent background sound is Ms-Pac is missing completely.  I've watched video reviews on Youtube and the sounds in the videos are correct, so I know it's not bad emulation.  I've searched the forum and haven't seen anyone else with this issue.  The game uses 1 very small board for everything so it's kinda hard to isolate what would be the equivalent of a sound board.  Any ideas?   Thanks!