Having recently fixed the DECstation 5000/240 PSU, I wanted to see that the machine actually runs properly and can run an operating system. I had previously had another DECstation 5000/240, which I had swapped for something else, but I had kept the disks where I had installed Ultrix and two versions of NetBSD, so I decided to try these first.
I found that the NetBSD 5.0.3 disk will no longer spin up, which is a shame, but may be fixable, so I will look at it again at some point. The NetBSD 1.5.3 disk would boot up to a point and then hang. The Ultrix 4.4 disk booted but the screen went blank once it went to the graphics mode. I suspect that the NetBSD 1.5.3 and Ultrix 4.4 installations don’t like the PMAG-JA graphics card.
I found another spare SCSI disk, a Seagate ST12400N, and installed Ultrix 4.5 on it successfully. Sadly, when I switched it on again later the disk would not initialise. I could hear it seek a few times and then spin down. So I decided to overwrite the Ultrix 4.4 disk, an RZ56, with a new installation of Ultrix 4.5. Here is the setup I used:
I used an RRD43 that I have. The tray won’t stay closed properly, so you can just about see the head of a screwdriver that I propped against the tray to keep it shut!
The first attempt failed after what looks to have been a file copy verification error, so the disk can’t be too good. A second attempt succeeded, here is the machine working:
Rob's Old Computers 
Hello,
Im the former maintainer of NetBSD/pmax which is now folded into NetBSD/mips.
I never had a PMAG-J so I never thought of adding support. NetBSD/alpha may have added support. If so the driver will work on both mips and Alpha TC machines.
I am resuscitating my stack of DECstations which have been in storage for over 15 years. Rather than buy used, 20-year old SCSI disks, I am trying a SCSI-to-SD adaptor with a 32GB SD-card. I’ can let you know how that goes.
I am also looking for a TCE box so I can work on the 2- nd 3-TC-slot graphics boards. Be warned, the TC-Extender is mechaincally 3 slots, but electrically it’s just one slot. It’s intended to support the 3-slot “option cards” like the PMAG-F. That’s why if you tried mulitiple TC option boards in the TCE, the boot-ROM and OS will only see one. Rusting is what they do; every PMTCE photo I’ve seen shows rust. The TC-expander connector appears to use standard 100-pin Honda (SCSI-2 style) connector. A physically compatible cable is the ACL-102100-1 or -2. Mouser has them in stock. I cannot imagine why Digital would not use a straight-through cable, but there’s a chance the SCSI cable may destroy the TCE module.
If you want to give your TCE (or the FDDI cards) a good home which would perhaps contribute to better support for higher-end PMAG boards, do let me know.
After 15 years in storage, I may need your help with PSUs!
I have certainly seen a lot of rust on my TCE! I would really like to hang on to my TCE, especially as it was a lot of effort to get it working again. I did successfully use a 100-pin SCSI cable to connect it to the DECstation, so you should be fine with that. I *may* be prepared to loan my TCE, but I am in the UK and I don’t know where you are. Certainly happy to help with PSUs, although I am no expert and it takes me weeks or months to repair one. Best thing to do with PSUs that have been in storage for a long time is to check all the electrolytic capacitors for bulges and leaks, if you have an ESR meter, check their ESR too and replace any suspect ones before switching it on.