i had a mutant fighter that had artifact problems i pulled all the chips and resocketed them.. this solved it.
i also have a pitfighter.. 2player conversion kit, oddly one thats not been dumped and mamed yet.
it has some issues which i've narrowed down to what i believe is a short somewhere near the main CPU.
but i dunno how to track it down.
i narrowed this down by gently flexing the board in various areas while on.
probably better ways to trouble shoot this kinda stuff but i dunno them.
anyway sounds like a short somewhere, either the chips need reseated, or you have a short.. or maybe just a cold solder joint somewhere.