The plan from the beginning was to run NetBSD on my mono slab. This makes integration into the network vastly easier than with NeXTSTEP or OpenStep because of the wide availability of easily recompiled POSIX and BSD software. And I was looking forward to the challenge of running an alternative operating system on this machine since I already had one running OpenStep. NetBSD also has an entirely reasonable headless interface making it a snap to simply shove onto a shelf in the museum equipment rack and access it exclusively from the network. And since this slab arrived without the means to mount a hard disk drive inside the case, I decided I would run it diskless.
My mono slab arrived with a broken power supply, but that was easily fixed. I got that particular machine because it was cheap. Unfortunately that's when the actual pain began.
The slab itself doesn't have a power button. That's on the keyboard. But the keyboard doesn't plug into the slab, it plugs into the monitor…which I neither had nor wanted for this BSD machine. I was planning to run it headless. But that's OK, because shorting two of the pins in the proprietary video port provides the needed power-up signal. I even made a 19-pin D-subminiature shell with a momentary switch to do the "hotwire" power-up all convienient-like. Only then did I discover that the NeXT boot firmware doesn't automatically recognize the lack of a video monitor or a valid signal on the serial console, so my boot interface was going to the monitor and keyboard which I didn't have.
I ended up buying one of the remaining NeXT monochrome monitors for the sole purpose of breaking into the boot firmware and changing the setting that would send it to the serial port instead of the video and keyboard. These monitors are getting rare and they're all dying a slow death as their CRTs slowly dim. Remember how there's no power button on the computer or the monitor? In NeXT's ingenious design, you can't actually turn off the CRT which means as long as the computer is running, you're putting hours on the monitor. You could switch all the pixels to black and run the brightness down as low as it would go, but the tube heater continues run. There was no DPMS in 1990.
While I had the monitor, I installed OpenStep 4.2 and the Developer Tools to verify my media and confirm the hardware was in good working order before installing NetBSD.
Recall that this slab didn't come with the means to mount a hard disk drive, so I borrowed those from the NeXTstation Color and installed onto a spare SCSI HDD.
Everything checked out. I was finally able to boot my slab headless only to discover that the old firmware had a clunky BOOTP implementation that didn't work with modern BOOTP/DHCP servers that even my oldest Data General machines understood. This made booting diskless tricky. So I found an old BSD bootpd and finally managed to get NetBSD running on the blasted thing. I swear no old computer has been half as obnoxious to get running as this obsolescence-is-designed-in NeXT.
The NeXTstation Color made all of this somewhat easier because the NeXT Soundbox manages all the weird, proprietary connections and you just plug a common (at the time) 13W-3 monitor cable into the Soundbox. Easy peasy.