While perusing the internet recently I came upon this old gem. https://sites.google.com/site/ataripal/cartdump
Interestingly of the methods talked about to create a hardware cartridge dumper one of them is possible with my MMU Adapter by simply connecting four wires and a DPDT switch. I have tested that the hardware modification works, but then it becomes a question if the software(The Cartridge Dumper utility) created by Jindrich Kubec to dump to a file will work.
So far I have had little success in operating the software as is claimed in this internet article. A thread on AtariAge seemed to indicate that the little utility was never really meant for public use and therefore left much to be desired as far as user friendliness. I would have to agree. Perhaps someone can tinker with it and/or create a utility that will be more friendly to use.
There are other means to dump a cartridge to a file, and little reason to now as most carts have been dumped and are available for download. But the tinkerer in me likes to make my own just to see if it will work.
I have added the schematic to the MMU adapter documents.