Raymond Carlsen (rrcc@u.washington.edu) writes on the diagnostic cartridge he acquired for the Commodore 64: I've not had a chance to try the carts... perhaps today. I understand that one type of diag cart requires an "octopus" cable or "harness" that tests all the ports. Obviously I didn't get such a cable or any docs. Some info on what I have: The C64 cart has the number V586220 on a paper sticker after "C64 DIAGNOSTIC" on top. Inside, there is one 2764 socketed EPROM labeled U1, an empty 28 pin socket labeled U2, and a 24 pin board location without a socket at U3. There are no other components except a few caps and three "jumpers" (like a disk drive has for device #).