You most likely need a Torx No. 10 screwdriver or bit. Easy to open, and the revision number is plainly written on the motherboard.
I share your pain. I have an ACA500 I have been unable to use because it apparently does not work with NTSC Rev 5 boards. As far as I know, these are the most common revision boards in the U.S.
I need to find and buy a Rev 6 NTSC board.
