The peripheral tier on an M25 can accommodate three devices. Slot 1 (left) is usually the SMC backup tape drive, slot 2 (middle) is for use by the disk drive, but the right-hand slot 3 seems to be multi-functional. It's usually empty, or has a floppy (8" or 5 1/4") installed. However, looking at the backplane in detail and inspecting the backplanes from the three machines leads me to think you can add a second disk drive. There are a few tell-tale signs to corroborate this too.

If you look in the above picture inside the red box, there is a connector. On one backplane I have, there is a "bridging board" plugged in here.

All this "bridging board" does, is connect all the pins on the left, to their counterpart pins on the right. This has the affect of connecting the right hand slot connector in parallel with the middle slot connector.

Also, the data sheet for the disk drive states that the highest drive number should have a termination resistor pack installed. This MUST be removed from the other drives.

The above picture shows the inside of one of my M25 disk drive enclosures. You can see the configuration switch highlighted centre-left. Below that is the resistor termination pack. But look in the top right corner of the picture - there is a blue resistor pack. This isn't connected to anything and the resistance is the same as the yellow pack. This is actually a storage socket to hold the resistor pack when it's removed from the disk drive. No idea how this drive ended up with two packs (probably had the disk drive exchanged at some point). Both my other enclosures have this blue pack missing. So it looks like you are supposed to remove the resistor pack if needed, and store it in the empty socket.

I've still not been able to get a second drive to work. CONFPROG seems to be configured correctly, but when I try and mount the second drive - "INSTALL 0.2" I get an error "DISC ERROR READING INDEX" and the system just hangs. I know the second drive works as it's just been formatted and had an operating system installed and will happily boot a system if it's set as drive 0.

I'm missing something... but I don't yet know what... yet.

I've previously stated that I've obtained three M25s over the last few years and number 3 pictured above is in a really sorry state. I've no idea what happened to it but it looks like it's either been dropped or a lorry hit it. You can see the crack down the top of the left-hand side. Also, both the top and bottom tier cages are bent. Amazingly the backplanes are intact and all the plates and disk drive were still working when tested in my main machine.

Anyway, this thing has been taking up valuable space so I thought it worth removing anything of value and scrapping the rest. Absolutely everything electrical has been removed including the fans and plastic plate-slot blanks. The outer shell will go to the scrap-metal people.

However, I have a second chassis that's in a perfectly serviceable state once it's been cleaned, so I've decided to construct a second machine.

I'll be taking pictures thought it's rebuilt process, but not during it's tear-down. This second chassis was absolutely filthy and mice had been living in it and I didn't fancy having to keep washing my hands to hold my camera just to take a couple of pictures. You will be able to view the re-build pictures in reverse if you want to see how to tear-down a system :)

As for what I'm going to do with it, it will replace my current chassis as I cut a couple of corners when cleaning it originally, and there are a couple of jobs that I wish I'd done.

Once this second chassis is up and running, I'll gut the first one for all the useful bits and either drop it on Ebay as just an empty chassis (at least it's clean), or off to the scrap metal dealer. Nobody except me seems to what this stuff anyway.

After pulling my hair out as to why I couldn't get a second port working, I posted the question to the Nixdorf group on Linked-In.

Quick as a flash Malone came back with some useful technical information about cable part numbers to use, which whilst completely different from mine I was still pretty sure that my wiring was correct, and also made a comment that the second ALME channel on the first ALME is reserved for the remote support connection.

I'm sure in the past I've used this channel for a normal VDU connection, however, it was worth a try.

He was dead right. So, another useful lesson learned.

Thanks Malone for the valuable info.

I wrote my first decent business BASIC program last night. Amazed at how much I'd forgotten but it slowly came back - working in Visual Basic for 20 years hasn't helped.

I wanted a routine to search through a specified list of files and look for pieces of text.

The LIBR list file contains all the *C (contiguous) files that are likely to contain German text that's used by the operating system. For example, I wanted to find where the machines original owner name was stored - In MESSAGES, record 147 for the record.

It was a fun exercise and a real blast of nostalgia. I really need to get a second terminal up and running as just having the one is a real handicap.

I've actually managed to repair a second terminal. Next I need to assemble a suitable connecting cable for it.

As an update to this post, I've been messing around all day trying to get the second DAP4 to work over an IHSS connection for I'm having problems for some reason.

I know the DAP4 works ok, because if I put a V24 card in it and connected to the master port channel on the ALME it works fine. I've tried a different ALME and it's not that.

So it's either a problem with the interface cards (and I've tried several) or the cabling but if it is I'll be dammed if I can see the problem. I'll have another go tomorrow if I get the chance.

I've been doing a lot of site updates over the last few days and I'm not finished yet. I've added a pile of stuff to the hardware page, especially under the tape and plates headings including articles on how to service SMC drives and attempt to repair a damaged tape. There are also lots of high resolution photographs of all the plates I have plus other technical information.

Still lots more to do so keep checking back.

Update...

The nice man from UPS just delivered my replacement SMC drive wheels that Tandberg so graciously gave me.

Looks like I know what I'll be doing over the weekend now.

Major spare parts testing was completed last night.

I'm suspicious of the 1830 hardware arithmetic unit but that could be because I'm not 100% sure how to configure it in NIROS. I know you have to deactivate $DEC14H then activate a $DEC18H driver in it's place, but I've got a niggling feeling there is something else that needs to be done. It could be one or more DISCUBS but I just can't remember.

Whilst I have an 8" FD and a box of new discs as it happens, I think that either I've got the wrong controller (apparently it's for a 5" FD not 8"), or the controller / FD is faulty as the system becomes unstable when it's installed, but I need to experiment more with this.

I've not tested the PLC2 I have because to be honest I don't need it and it's certainly not a requirement for a minimum running system. Also, if memory serves you need to have the BCU (Batch Communication Utilities) software (or the MAFI), and I don't.

The only failed parts I have that are required; excluding the 2 x SMC drives but see a previous blog about those, is a 3109-02 PSU. I've got two working ones but the 3rd is playing up.

I suspect it's a leaky capacitor. Electrolytic capacitors don't age well and really don't like high temperatures, and a high proportion of failures in any SMPS (switch mode power supply) can usually be attributed to leaky or failed electrolytic capacitors. There are 16 high-value capacitors in this PSU and a job on the list is to get replacements then swamp them all out. It will either work or it won't... it's one of those types of repairs.

The 8870 modules are unfortunately packed with tantalum capacitors which, IMHO are the spawn of the devil as when they fail they nearly always go short circuit usually with pyrotechnic results, along with a smell you wouldn't believe. This PSU contains several so I'll probably swap them out for safety, if replacing the main electrolytic capacitors fixes the problem; pointless otherwise.

So, all in all and except for DAP4 replacement parts, I'm in pretty good shape for now.

I've been testing my 3 x SMC drives over the last few days. They all needed servicing first (and I'm just in the middle of uploading an article that says how to do this), and then I wanted to test them to check they worked. I'm also paranoid and thought that at the same time I would make several operating system tapes... just in case.

The SMC drive I've been using by default has been fine so far, but I've noticed that I've been getting "please clean the SMC drive" type messages popping up... and I've been cleaning it but still getting the messages. Now, I don't know if this is an automatic message that appears after a predetermined amount of time, or if the drive is detecting read/write errors and having to keep retrying.

Anyway, I placed in the first of my spare SMC drives but it would either fail to format the tape, or would just mangle said tape. Luckily I've got a pretty good stock of tapes; old and new.

The drive was clean but the rubber drive roller wheel is perished. If it "looks" ok, when you clean it if it leaves a black tar like substance on the cleaning wipe, the wheel has had it.

Ok, on with the second drive. This had exactly the same problem.

So I'm down to one working drive currently. However, all is not lost.

The two faulty drives seem to be electrically sound and are in pretty good condition; it's just these rubber wheels.

I contacted http://www.dicolldata.co.uk in the UK to see if they could service the drives for me. I had a great chat with Mark there but unfortunate the best they could offer were replacement drives; they are almost 30 years old and it's not possible to get spare parts.

He said he would checkout the drives and let me know. A couple of hours later he called back but it was bad news. The drives they have also have perished wheels. It turns out that the rubber will perish on these wheels no matter how you store the drives. I'd hoped that them being stored correctly would preserve them. However, he gave me the number of another company who he had spoken with, and they had several working drives in stock. I gave Karl at http://www.ultratec.co.uk/ a call but after a chat he was also concerned that his drives were in a poor condition as well. He did offer to pull them from stores and check them over for me and I'm awaiting a call back sometime this week with luck.

On a whim, I found Tandberg in Norway and dropped their support department a pleading Email Supportemea@tandbergdata.com

Quick as a flash I received an Email back from one of their support engineers and too my surprise told me he has three wheels and he will happily send them to me.. free of charge.

What a result.

All being well, I can get the other two drives up and running and have a spare for my currently working intermittent drive.

This has been a really positive experience. Mark and Karl could have easily sold me drives with perished wheels that may have worked for a while before breaking, and Tandberg could have just thrown my email in the bin and ignored me.

So guys, if you happen to read this... many thanks for all your help and honesty.

It's been a while since I've done anything with either this website or my 8870's - something that I'm eager to change.

As time allows, I've been slowly collecting documentation, experimenting and just trying to get re-acquainted with how things work. I'm amazed at how much I've forgotten over the years.

So currently, this is the state of play.

I've actually got three 8870 M25 chassis. One is in my workshop and running fine. The other two are in the garage. With one of them at least, I've no reason to assume that if I added plates, PSU and a disk, wouldn't spring back to life, though it needs a darn good clean before I attempt that.

The other chassis is in a real sorry state. I think it's electrically sound but the plastic outer shell is in a terrible state. It looks like it's either been dropped or somebody backed a lorry into it.

I've removed all the "good" stuff from both the above chassis and I've tested all these items one by one in my working machine and so far pretty much everything seems to be working ok. This means that I've got spare disk drives, CPUs, ALMs, PSUs and disk controllers and if I had serviceable chassis I could built another machine if needed.

Still only got the one working DAP4 and no working DAP spare parts which is a worry.

I've got copies of the NIROS 3.3 and 5.0 manuals, and a BASIC 7.0 manual plus some other assorted operator and technical manuals - all in German unfortunately for me though I did have had the NIROS 3.3 manual translated to English.

I've one working ND11 printer, a couple of new ribbons and a SAS cable (printer to DAP). I've got another ND11 that's in the garage right now but I've not tested it.

I've a working Niros 7.0/03 operating system (German again unfortunately) but at least it didn't have User Administration installed, and I eventually managed to find somebody who knew the system password - my memory is terrible.

Interestingly, the first system that I obtained was running Niros EX but the disk was corrupted and the system eventually failed - it was deleting more and more files every time it booted which was a real shame. However, the curious thing was that it had a 1537 CPU fitted, not the latter 1559 that we were always told was a pre-requisite for Niros EX.

My current plan is to harvest the back planes and everything else removable from the damaged chassis, and I'll probably sell the other one as just an empty chassis as I'm not letting any of my spare parts go.


Anyway, that's the situation currently