On a happy note, the NIROS 3.3 manual translation to English is now complete; I just need to sort the document formatting but that won't take long. My translator did a pretty good job but there were some interesting oddities.
Reading the last part, I noticed the word "trail" kept cropping up... this should actually be "track" as the text was talking about disk platters. Still, it's perfectly understandable but I may update it.

Work is progressing on my EPROM reader / programmer unit. Schematics are completed, PCB layout is also just about done (am waiting for a parts delivery to just check board space for one of the connectors), and then I can etch, drill and assembler the PCB, and after all that, there’s some firmware and PC software to write. It’s going to take a little while to complete but I think it will be well worth it. It will be able to support reading / programming and testing pretty much any type of ROM / RAM or EPROM and once completed, should allow me to make some image copies of the ROMS/EPROMS using within the various 8870 boards and peripherals.

I've also managed to format the two 8870 M25 drives I have.

During my previous attempts to backup the system disk on my first M25 (backups that kept failing for various reasons), there must have been enough of the operating system copied to the tape to allow me to boot from SMC, and run the formatter program. The formatter took around 5 mins to run and didn’t find a problem on either drive.

A couple of things worth noting here for those that may need to know.
The system I have doesn’t like to boot from SMC on a warm re-IPL. You need to have the system switched off, power on from the master port, and then quickly insert the SMC and close the drive door.
If the system attempts to boot from disk (you will get a CPU #0 INIT or just INIT) prompt, quickly press the R1 to R4 keys on the master port. I can’t figure out which of these keys actually interrupts the IPL process, but one of them does You can then tell the system to IPL from the backup tape by entering a “1” next to the INIT prompt, and pressing CR when the cursor appears.

You will eventually get a short Selector menu up on the screen (probably in German).
Option 1: Disk formatter.
Option 2: System recovery
Option 3: Shutdown

Options 1 and 2 need to load software from the backup tape, so give it a few minutes to load.

The other thing I noticed is that there was a LOT of SMC tape transport and the system was constantly moving the tape. This seems to be normal but takes some time so be patient.
Also, on a DAP 4, you may see the L1 to L4 lights flash, or change status every now and again and once again, this is normal. The DAP workstation program is also loaded from tape.

Those that have read my previous posts will know that the only operating system I had was on one of the system drives and was badly corrupted, so I had nothing to lose from formatting the drives just to see if they are actually serviceable; don’t try this at home unless you have SEVERAL copies of your operating system securely backed up on tape.

So, it looks like the drives are ok, and I just need an operating system... anybody ????