Using MAME as a debug tool

To generate the screen shots shown on my technical pages, I took advantage of MAME (Multiple Arcade Machine Emulator). Mame can be a very powerful tool, as well as the MAME source code contains very valuable game information. Using the MAME screen snapshot capability (F12) I was able to capture perfect pictures of what the screen looked like in both normal conditions and in failure cases. (I still needed to convert the images to .jpg files and also had to create thumbnails).

For the fault cases, I made a common assumption that when a prom or eprom fails, that it reads back all ones (0xff). To insert the fault, I would, replace each ROM file used by the game with a "faulty" ROM file that contained all ones (0xff).

So, one by one, I would save a copy the original ROM file, then overwrite it with a "faulty" ROM file of the same size, but that contained (0xff). Then I would run the game and see what happened. Assuming the game would function, I would then take various snapshot images of that particular failure. I would also keep notes of what images (as MAME will number the images sequentially) matched with which chip failures. Then I would restore the original ROM file, and move on to the next. One by one I would eventually cover all the ROM for the particular game.

For some games when the main CPU roms are replaced with blanks, the game will not even execute at all. Those failures are not as interesting from a video perspective. However, some games, like the Donkey Kongs, have lots of character and sprite eproms.