The battery holder on my MM is broken, I am missing the (Auto Up/Manual Down, Advance, High Score Reset) button set, and I do not care to keep high scores so I finally got tired of going behind the machine with a wire and figuring out how to hit advance and add credits everytime I power it up (rarely). So instead of doing the simple thing (soldering a modern battery to the board), I decided to monkey with the code to solve my problems!
The results are the text file describing my process and the 3 EPROM files. Maybe this will be helpful to *THE* other MM owner out there. ;-D
Burn one of the EPROM files into a 2764 and then replace EPROM 17 (IC 25) with the new and improved EPROM and have fun!