I'm not affiliated with the maker, but just thought it was a cool product that allows you to test a lamp matrix for errors right off the CPU board. Especially helpful for a quick test before you buy a machine. This is a video of me testing my JP for what I already knew, row 5 is out.
The kit comes with everything you need except a molex crimper (you have to assemble it), just tell them what era machine you're working with and you'll get the correct connectors. Or, just buy multiple sets and have a setup for pretty much all machines.
