Read through all the messages and incredible work you've done to resurrect this old IV/90. I was a systems engineer for Four Phase from 1984 to 1989. The IV/90 was the last Series 4 that Four Phase delivered, redesigning the system around 1982-83 as the "Series 5000". Sounds like you could use a Field Engineering Guide, which has the hardware engineering details for entering into self-test diagnostics for components, by inputting the execution addresses in the 24 switches and register selection switches on the front panel. There are a couple Four-Phase alumni groups on Facebook, there are some engineers and product development folks there that may be able to help - some of the alumni also have chips, parts and probably even microfiche (which is where we kept out documentation. Would be happy to help, or try to answer any questions about the system and it's use. I saw the NP/80 (my favorite processor!) and what looked like two of the first "sealed disk" technologies made by Fujitsu - I think they are 128, 256, or 512 MB of storage. The NP/80 handled all "new" disk storage (at the time, LOL), either the Fujitsu drives, or a model 8260, 60MB removable disk. There is only so many diagnostics that were ROM based, once going through those tests, you had to set the boot devices on the console, and boot up diagnostics. Oh the memories.....