The Mediator board use up to six Mach chips, coded by Elbox, so you need the Multimedia CD (from the guy who sell you the board) and the chips from Elbox.
Notice there is not a way to duplicate a Mach chip (or any other programmable PGA chip) if the protection bit/fuse is set/open. Buy the replacement chips from Elbox directly!
BTW: test the pass-trough card before start messing with the chips. The most common source of Mediator failures is just that little piece of crap.
I had a very hard time fixing one myself!
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How to test? simply put the pass-trough between the 1200 motherboard and the accelerator. The Amiga must be running like always.
If the accelerator don't appear or you see the "hardware failure" screen, the passtrough is doomed.