Since I likely won't have time to make a more official 'document' for a while (with podcast production and Classic Gaming Expo preparations, not to mention 'real life' responsibilities), I'll just post my scanned paper notes and diagrams that I made as I worked out the differences between the two controllers.
The first thing I did was place the 2 matrices side-by-side, flattened out. Then with a multimeter, I made sure each "zone" (for lack of a better term) of the Flashback matrix matched up with the corresponding zones of the original matrix. For those who don't know, basically the Intellivision controllers send multiple signals on different pins, depending on what buttons or button & disc combinations are being pressed.
Once I knew the traces and zones were the same, it came down to mapping which zones went to which trace ends, and what the corresponding wire / pin was on the plug.
Note: In my images, the numbers, symbols and colors I used are just arbitrary things I created as I mapped things out.
Edited by nurmix, Tue Aug 26, 2014 1:12 PM.