MK14 schematic revisions

[Timbucus]

It seems you can now buy one of the V1.2 boards on ebay...

https://www.ebay.co.uk/itm/184327189174?ul_noapp=true

[Slothie]

Well.at least they didn't take my name and logo off it.

[SiriusHardware]

I was rather afraid that might happen. Although it was good of Ian to make the rev 1.2 available to be beta tested, I suggest any further revisions remain his to get made and to sell, and the same for any other boards he produces such as memory expansions, etc.

[Timbucus]

Looking at the listing it is someone who has had a small batch made and is selling the extras I think. Maybe they were more expensive to get made than ours - let's hope it adds some extra MK14 enthusiasts who find their way here but, it is a shame Ian does not see any reward for his hard work.

[Slothie]

I have the reward, I have a working MK14 and the knowledge I picked up on the way, and also the knowledge that I have made something other people appreciate.
As for anything further? Well maybe under my current circumstances I might keep designs private until I've made a little from them. I'm mainly in it for the fun and nostalgia, and 'meeting' people like you guys.

[SiriusHardware]

Without the new PCB I would never have considered connecting the SOC VDU up to an MK14 again, the routing of the address, data and control signals to the rear edge connector, along with the all important memory hole at 0200-07FF (another thing my original machine does not have) are what made it for me. I love my original old issue II machine but its early PCB severely limits it in some ways and I could not consider modifying it in any way for any reason now.

The problem I have now is that the issue VI replica is just too nice to modify or hack about for any reason. I know Tim wants to boldly go where no MK14 has gone before with his, but I'm content for mine just to be the MK14-GTi I always wished the original machine had been.

I assume Phil in France has one either already or on the way to him, although he seems to have a lot of plates spinning so it may be a while before he is able to populate it.

[Slothie]

Oh well Sirius there's always 1.3 to look forward to.. then you can build one to keep and hack the 1.2! I

[SiriusHardware]

If there had been just one or two mistakes on the PCB which made it necessary to cut tracks and add links to get it working then I wouldn't have minded doing further messy mods to it whenever the mood took me but as it is, it looks so smart / neat that I wouldn't want to do anything to spoil that.

I have tact switches on the way now so I will be printing and cutting out a set of key legends from the scans posted here recently and hopefully it will look even nicer in the not too distant future.

[Timbucus]

Same here - I have even swapped the green key tops for black and my red reset switch for black as well - I will keep a look out for a black axial cap to swap for my Yellow one. I think my legends will be printed inverse white on black to complete that 'Black Edition' look.

I know you think I want to mod it heavily but, actually I think a plug in "black" NIBL board on the CPU will be non-destructive and just need the omission of some of the chips which is the route I wish to go down. The memory and VDU will be on DIN connected expansions from the back and will continue to be best used from this Ian Issue VI. That plug in board will even likely work with my JMP or the Martin V one if it is designed correctly.

I am now thinking I may have a craft project one day to make a copy of the SoC Kit Box to keep my Martin Issue V in as a smart display and useful way to store a set of spare parts for this and my JMP - which I would like to get the V1 SCIOS burned for at, least to experience it as I cannot see it being used that often now.

[SiriusHardware]

You could always sell the JMP replica, I have seen even replicas go for astoundingly high prices, even taking into account the increasingly high cost of populating one of these PCBs now. (The SC/MP, 4 * RAMs, a pair of programmed PROMs and a suitable display and a set of key switches can easily set you back well over £150, especially if you prefer to avoid the minefield of buying from China. And that's without also adding the optional INS8154 I/O IC).

I think there is no sadder sight than an unbuilt kit (of any sort, be it electronics or 'Airfix') so I think it would be a bit mad to never build the 'Martin' kit and put it in an authentic box if that is what you are contemplating, but I would certainly urge you to make high quality scans of both sides of that PCB because who knows when Martin may cease production of them? They are 98% SOC's issue V, the layout is only different in the specific area of the dome switches as far as I know so I think there is a valid case there for archiving the track layout just in case.

As far as the original SCIOS is concerned, there is a reason that got replaced - it was very clunky compared with the 'new' OS, even my original issue II has had the 'new' OS since as soon as that was made available as an after fit option, some time in 1979 probably. I still have the original PROMs - no idea where - but they are never going back in.

I think the only good reason to fit the 'old' OS is if you also have an original V1 paper manual because then you might want the machine to work as described in the manual if you plan to sell the machine and the manual as a 'set'.

[Slothie]

Well.when I get my stuff back I'll have a number of spare 1.2 boards if someone wants one to hack.

[SiriusHardware]

I'm holding one of the black PCBs for you and I had intended to offer up the remaining black rev 1.2 PCB for exactly what it cost to have made and posted to me: £5.

I won't be doing that now though. I'll probably keep that one as my 'hacker'.

[Slothie]

Good. One of the great things about computers from this era was you were supposed to modify and extend them. I can completely understand not wanting to mess with your original considering the rarity, however.

[Timbucus]

Originally Posted by Slothie

Good. One of the great things about computers from this era was you were supposed to modify and extend them. I can completely understand not wanting to mess with your original considering the rarity, however.

Indeed hence my 'Inversion' hack for the VDU - in fact it is the very nature of these, as ancient arduino's, that has attracted me away from my other retro interests to allow the reconnection with code and electronics as a pair.

I may take you up on the green 1.2 option as a hacking board!

But, I am unlikely to sell the JMP just because of the eye watering cost of some of the chips which are bound to fail (as I have found to my cost) - as I experiment...

I will take building the Martin Kit under advisement (but, will scan the board) I have a few other projects that are nearly parts complete first - as I robbed a few for the Issue VI...

Anyway here is the pair now (I decided to complete the Issue VI inverse keyboard printing) in the second photo I have also made up one of the new displays to prove they work - they do but, you need to clean the pads to get any solder to adhere and it still looks like I can do solder blobbing only...

[SiriusHardware]

Aww, those keys look so nice. I might do mine in conventional black text on white for purely practical reasons, I find it hard enough to read the dim white-on-black legends on this computer keyboard in anything less than perfect light nowadays.

But there's the beauty of the clear keytops system, you can do them one way and then change your mind 5 minutes later. It might be worth buying a full extra set of the clear covers and keeping them in a light proof container because I have similar (but much bigger) keyswitches here from the keypad of a 1970s EPROM programmer and the clear covers have gone tinted yellow. Mind you, the age we all are now, that probably won't be our problem to care about by the time it happens to these key caps. It probably is worth having a few spare key covers, key tops and key switches though, as those are the sorts of things which could fail or get damaged or knocked off over time and as we all know a missing knob or switch cap can have a disproportionate effect on the aesthetic appeal of any item of equipment. I even have four spare switches for the homebrew keypad on my original MK14.

The JMP PCB with its beautifully designed companion keypad looks really classy, it's only due to the fact that it lacks some of the final refinements (PROM images are not removed, no edge connector contacts on the underside) that I haven't got one myself - I already own an original MK14 with exactly those limitations and a fairly decent keypad so the JMP version PCB would not give me anything I don't already have.

[Slothie]

Those JM keys look nice, and the others look good with the black caps look good too. When I get a 3D printer I hope to make a frame to align the switches because the caps do tend to swivel slightly out of line. If the frame was black and the keycaps white it would also make the board look closer to original.
Now, if I could find a source of INS8154D chips for a non ludicrous price I would be happy! I've got 2 but I have no idea if they work, and I'd like the option of getting more as they'll be useful for future projects... Just a case of keeping an eye on t'internet I suppose. I would never have guessed that it would be the one chip that's hard to find considering how widely it was used at the time.

[SiriusHardware]

Failing all else you could always send the ones you have to me or Tim... if he promises not to connect them up to anything... for testing, but I doubt whether you have them in your back pocket just now.

[Mark1960]

As suggested by Sirius, replying in this thread for how I ended up with an MK14.

I bought it second user, already built and in a simple wooden tray in about 81 or 82, too long ago to remember accurately. It was in a classified advert in either Northern echo, south durham times or possibly even the Newtonian, which I guess some will identify as putting me not far away from Sirius.

The original owner made quite a good job of building it with some very nice red RS component IC sockets for all except the processor which is a boring low profile socket. I added the 8154 socket and the 8154 itself after buying it in a blister pack from Tandy in Darlington soon after aquiring the MK14. I still have the printed spec sheet that was stapled to the back of pack somewhere, together with the original MK14 manual.

I 've recently been able to get it running again after sourcing new RAM chips. I think the original owner took it a bit too literal when directed by the manual to add solder sparingly and a couple of the joints had broken due to the pins being bent backwards and forwards a few times. Suspect this caused some bus contention. I removed the 8154 fairly early in the attempt to get it running again so hopefully it has survived. I've also removed an external ram board that I had connected.

I've been trying to find some matching sockets to add the extra ram, it just doesn't seem right to use modern sockets on what is possibly a museum piece.

It's a rev IV, with the individual switches, not the metal dome keypad, and it can still enter some of the programs from an online scan of the manual. It does take some practice to avoid double key entry by picking the best position to press on each button. This is a bit of a surprise as it has spent much of the last 20 years stored in a bubble pack envelope in a damp garage.

I'm interested in experimenting with the sc/mp again but don't want to cause any more damage to the old MK14, so thinking about building something along the lines of the RC2014 but using an sc/mp. Still trying to decide if I can trust the parts for sale from china. It would also be interesting to try the INS8070, but they seem even more difficult to find.

I don't seem to be able to add pictures yet, but maybe this is another part of being on probation on this site.

[Timbucus]

Mark - I don't remember a limit for posting pictures but, I have seen and bought some of those red Camion sockets on e-bay recently - in fact my Black MK14 VI had one of them to start with but, it was stripped off when I damaged it which is a shame as they look really cool.

Maybe you would like to join our effort to rebuild the SCRUMPI - other threads are available.... that is a real experiment in SC/MP...

I did comment in the VDU thread before I noticed you had changed that your observation on the Virtual Memory support was interesting as page exceptions could work in that way, an interesting project. I propose though that the reason was the Multiprocessor support which was baked in. You would need to deal with data changes part way through cycles for that to be deterministic.

[Mark1960]

Hi Tim, I did see the red cambion sockets but they look to be low profile types, though I do think they would look cool using a full set on a retro build. The RS sockets are a slightly darker red and have what would have been called standard profile back in the seventies, they also have the RS logo printed in white on the side. The RAM has been mounted using two nine pin SIL strips, no logo on the side but very close match for colour and height. I think the blue cambion sockets are closer style to the RS standard profile sockets, it also looks like they have similar pin numbers moulded in the plastic, so maybe they shared some tooling.

For multiprocessing it seems possible to piggyback an sc/mp on top of another, with maybe three or four pins cross wired. It’s probably a bit destructive given the rarity of these parts now. Address decoding could override the nenin and the other processor could copy memory contents or update a memory mapper then reenable the nenin.

Anyway first step for me is to try and get NIBL or NIBL-E running.