Im in the throws of trying to repair my 520ST. I have all the components to fix the keyboard. As of now the unit boots to TOS and immediately freezes. Im building a Diagnostic cartridge. Can someone tell me the most comprehensive diagnostic software for cartridge out there? Is there any new diag software still in development. Im pretty much a noob with Atari ST's. Ive got the basic eprom cartridges out there with 4 X 27c256kbit eproms on them that looks like the image below.