Re: I found it! A very sorry looking MK14.
 

I actually already had file copies of the 'new' OS PROMs read from my own SOC supplied originals quite a few years ago now - but until I had your PROMs the first time a few days ago, I had never had file copies of the 'Old' OS read directly from SOC supplied PROMs.

I do now though, and as you say, they are well worth having just in case.

Re: I found it! A very sorry looking MK14.
 

I'm hoping this weekend to put the Vicky board into the Micky cabinet, so I can test my peripherals.

First up will be the display. I don't evisage any incompatible connector issues here, as the bubble LED is working fine, so the layout of the LED connector must be the same as a real MK14.

But what about the keyboard connector, is that the same ?.

I know I'm going to have to tread carefully around this connector, as I can see I've cut a track and soldered a link on Micky, but I think they're both something to do with the reset button. ( I seem to remember the SoC instruction text for removing ROM images also did something with the reset circuit. It might be that. )

So, apart from the GND and reset pads ( the first two near the reset button ), are the other pads in the same order as a real MK14 ?.

Cheers,

Buzby

Re: I found it! A very sorry looking MK14.
 

The mods for removing the unwanted PROM images 'stole' one of the two inverters which were originally in series on the input of the reset circuit, so the reset -switch- circuit is then modified to take the reset-circuit input high when pressed rather than low.

The issue VI keypad connector is the same as on all original MK14s, thankfully, except that one of the two 0V fingers at the top end has been repurposed as an external reset input. Since external keypads don't usually use those top two connections, that would not usually be a problem but maybe one of your many add-ons picked up a common 0V from there?

Re: I found it! A very sorry looking MK14.
 

I just thought I'd clarify that on my issue Vi the external reset connection on the keyboard connector is active low, i.e. pull to 0v to reset - the reset circuitlry is the same as issue I-IV and different to issue V.

Re: I found it! A very sorry looking MK14.
 

Yes, sorry, I was describing the likely modified reset setup on Buz's 'Micky' PCB. Of all the original and replica PCBs, only the original issue V and the Martin L replica have 'active high' reset input circuits by default. Earlier issue PCBs which were modified to remove the unwanted PROM images (like Micky) will also have active-high reset inputs.

The issue V came with this modification already implemented on the PCB.

Re: I found it! A very sorry looking MK14.
 

Buz's new-OS PROMs have arrived back and I'm just about to have a look at those - as he pointed out, the thermal label on one IC looks rather dark, and I don't remember having noticed that when I last had them. Attached, a photo I took of the PROMs working in my issue VI the first time they were here a week ago. There's no sign of heat related darkening on either PROM label at that time.

Even when working normally these devices certainly are hot-heads, when I programme pairs for other people I always place the blue and green sticky dots at one end of the devices unlike the SOC practice of putting them in the centre, right over the hot core of the IC. They don't need anything to make them run hotter than they already do.

In other news, my 4 * AM9111s arrived from the source in Germany - I've done a quick test on them all and while three work, one is unfortunately faulty. They all look absolutely brand new, legs still splayed suggesting that they had never been in a socket before I put them in my tester.

I'll get back to the supplier later to see how they handle returns. I doubt whether they have the means to test these themselves and I'm sure they were supplied in good faith.

Re: I found it! A very sorry looking MK14.
 

...Not good news on Buzby's new-OS PROMs unfortunately.

It turns out that the 'darkened' IC ('2o') is actually the good one, that reads / verifies perfectly against the code file I have here. But when I read '1o', the first 256 nibbles read correctly but every address from 100-1FF reads as 'F', so that is looking like a failure of the internal address decoding logic to me. I've done basic checks like resistances of all pins to the VCC and 0V pins but A8 on the dud IC reads no differently to pins A0-A7.

The only noticeable difference is that where '2o' has a resistance of >6M between its supply pins, '1o' has a resistance of 171K.

If it had been a case of finding a single bit stuck low somewhere I would have tried overprogramming but I don't think there will be any benefit to doing it in this case, where clearly the whole upper half of the IC has gone Missing In Action.

Re: I found it! A very sorry looking MK14.
 

As I said, the only luck I have is bad luck !.

I'm not too bothered at the moment. Now that Vicky is running, even with 'old' ROMs, I've got a basis to start work on Micky.

Hoping to get started working on it tomorrow, I'll keep you informed.

Cheers,

Buzby

Re: I found it! A very sorry looking MK14.
 

Well, the good(?) news is that only one of two is duff, so if you can source a single replacement Nat Semi DM74S571 and get it sent to me I will programme it for you. That will probably be cheaper for you than buying a pre-programmed pair. Just try to avoid any which are suspiciously cheap, as they may well already be programmed.

I've also had a response from the German seller of the AM9111s, they are sending me a replacement for the one dud IC out of the four I received.

Re: I found it! A very sorry looking MK14.
 

A quick update on the AM9111s, the replacement for the dud IC has now arrived and is OK. The supplier was very civilised about it so I'd be more than happy to use them again.

Re: I found it! A very sorry looking MK14.
 

I'll confess to having bought 4 from him, so thats good news. With the 4 I got from Mark I now have 8 chips, so I should be able to get 4 working ones!

Re: I found it! A very sorry looking MK14.
 

Hello All, I'm still here !.

There's been a lot of domestic issues, hospitals and stuff, since Christmas, so I've not had a chance to look at Micky till now.

I've built an 8060 NOPulator, and got one of those £10 logic analysers. From using these tools I've learnt a lot about Micky.

The main thing I've learnt is that every IC socket is rubbish. Not a single one is reliable. This especially includes the 8060 socket.

To replace this socket I will have to desolder most of the ribbon cables that connect the daughter board. However, without these connections there will be missing address decodes that the main board needs.

So I've decided that I'm going to restore Micky back to nearly original, without the extra RAM/ROM and single-step that the daughter board provided.

To do this I am going to replace the dodgy IC sockets, and re-wire all the cut or missing tracks. I'm sure this will be easier than debugging both the main and daughter board together, with not a single reliable socket on either.

What do you think ?.

Cheers,

Buzby

Re: I found it! A very sorry looking MK14.
 

I have to admit those flat-top IC sockets with the square holes in were never my favourites. The only word of caution I would offer is to warn you that the pads on old fibre glass boards of that period are very, very easy to burn off the board because the bonds which keep them attached to the PCB are not very heat resistant now. Lower-side pads which don't have tracks going to them are especially prone to this because there is nowhere for the heat from the iron tip to run away to.

I don't know if you have a 'proper' electrically pump assisted, temperature controlled desoldering gun but I would seriously suggest you might want to invest in one for this job if you don't.

I would say get it working in its original stand-alone MK14 configuration but then gradually take it back to something like its expanded form with the keypad and display extended to the enclosure, and reinstate whatever is needed to drive the binary LEDs and binary switches so that everything on the outside of the enclosure works the way it originally did.

Certain enhancements - like the ability to choose either the new or the old OS - with hindsight, are probably not necessary.

Re: I found it! A very sorry looking MK14.
 

Tough choice to make as it does remove a lot of the history of your original MK14 and all your custom mods, though I guess you could recreate those again after you have it working.

Mine has been showing some intermittent connection on the ram chips but can still be persuaded to work.

Are those TI IC sockets on yours? They were poor at the best of times and those socket strips were even worse.

Maybe you could try and get a set of cambion ic sockets to keep the period look. Turned pin sockets would look too new, and would be very difficult to replace in future, if ever that was required, without damage to the board.

Did you consider stripping the board to scan both sides? Or is that going to risk damage to other components?

Re: I found it! A very sorry looking MK14.
 

I would say it's not necessary to scan the PCB as it is issue II, I think. What we really want for the archives are scans of an original issue V.

I would second the use of (modern) conventional IC sockets rather than turned-pin, not because of how TP sockets look but because they would be near impossible to remove from an old double sided board, if the need ever arose, without doing damage to the pads.

I used to like the 'low-profile' type where the IC sat really low down and the top of the IC was almost flush with the tops of the sides of the sockets.

Re: I found it! A very sorry looking MK14.
 

The bare metal sockets are Molex 'Soldercons' which came in a continuous strip. I used those (versatile and cheap!) for many years/projects. Allowed access to tracks and running wires below each IC.
The basic version was tinned brass. In your picture many are looking grey, oxidised by the unsympathetic storage.
Any further soldering without a (scrap?) IC fitted will ruin the pin alignments.

Re: I found it! A very sorry looking MK14.
 

Maybe a tin of deoxidiser would be a good first attempt at restoring the sockets? I would be tempted to remove the extra items (after documenting) and then see if you can get it working with the least amount of desoldering after restoring broken tracks and replacing any chips. I have just invested in a desolder gun and wish I had done it years ago...

Re: I found it! A very sorry looking MK14.
 

Briefly OT, which one Tim? I was introduced to them in the early noughties and I wouldn't even think of not having one now.

Re: I found it! A very sorry looking MK14.
 

I bought the Duratool one which is often offered around £90 (It is currently £150 again on Amazon - just keep your eyes peeled) - I had seen mixed reviews but, had a job (my ZX81 Memopak 16K) that would have been impossible without (The edge connector) and I will likely need to desolder each RAM chip although I suspect not all will be faulty. I have some funny effects - I may create a post on it to help track down the issue. Sadly the first unit I had delivered was faulty but, no quibble another arrived within 4 days and works great as long as you leave it heated and clean the nib before letting it cool.

/END OT/

Re: I found it! A very sorry looking MK14.
 

That's the thing, they are very high maintenance, but worth keeping in tip top condition. One thing you should never do is try to clear a hole which you suspect might have a broken component or IC pin in it, once something like that gets jammed in the narrow channel in the nozzle, it's never coming out.

Re: I found it! A very sorry looking MK14.
 

You will laugh then when you see the video - almost every pin from the chopped off edge connector de-soldered from the expansion board at the back as well as the hole and got sucked into the channel - luckily as they were fat and cut off they jammed poking out and a pair of pliers allowed them all to be removed... luck rather than judgement.

Re: I found it! A very sorry looking MK14.
 

Thanks for your ideas.

Regarding losing my 'custom mods', the 5mm LEDs and switches on the panel connect to the 8154 via the edge-connector, so they will still work.

The 7-seg display LEDs are connected with a plug and socket, so they will still connect as before.

The keyboard again is on the normal edge connector, so no change there.

The only part of the daughter board that affected the front panel was the single-step switch, and as none of the toggle switches were labeled, I don't see that as a major problem.

Regarding removing the IC sockets, using a powered desolderer definately sounds like the best route. I'll look into them.

Also, I've found the original manual, the instructions for the cassette interface, an update leaflet for the 'revised' monitor, and a few other pages about programming.

To top that, I found my notes for building the daughter board, including a description of the 32 way connector.

I'm back on track again !.

Cheers,

Buzby

Re: I found it! A very sorry looking MK14.
 

Excellent that you have found the documentation - especially the daughter board.

I shall look forward to more updates on the project... and I am sure we will all render opinion as needed :)

Tim

Re: I found it! A very sorry looking MK14.
 

I was looking for one of those solder suckers recently but could only find the 240v version on amazon. 240v is available here, but uses two 120 v live supplies with 180 degree phase, maybe not a good idea to try and use uk 240v powered items.

Re: I found it! A very sorry looking MK14.
 

If you really want to replace those TI sockets, then the easiest thing to do to minimise damage to PCB tracks is usually to pull the tops off first, leaving the pins behind. You can then just heat each pin up and pull out one-by-one.

Back in the 80's, I used this to remove lots of these from some surplus PCB's, and then reassembled the sockets to reuse as I didn't have any stocks of sockets (well I was still at school then, and Maplin shops had only just started to open around the country / didn't want to pay Tandy's prices!)

You may also be able to clean pins and carefully push the tops back on.

Although these TI sockets never had tight grip pins, I didn't have any trouble with them back then. And I still use some very similar looking DIL16 & DIL14 Cambion ones (with 2 Kapton tape strips on underside to stop solder going into socket contacts, rather than single white plastic piece on TI ones), that I bought a few hundred for a few pence each from a surplus place in the early 90's.

Some contact cleaner spray into sockets, and cleaning of IC pins may also work quite well. Even just lifting IC's and re-inserting a few times may work for a while.

Re: I found it! A very sorry looking MK14.
 

Hi All,

I've got the crappy IC sockets off, and only lifted one track !. The TI sockets are gold-plated, so I just cleaned them with a squirt of isopropanol and an electric toothbrush.

Now, before I fit the new sockets, I need to re-make the tracks I cut 42 years ago.

Are there scans of the Issue 2 board available anywhere ?.

Cheers,

Buzby

Re: I found it! A very sorry looking MK14.
 

Not seen a clean scan but, snatched the attached clean-ish photo from a bay sale in 2019

Re: I found it! A very sorry looking MK14.
 

Don't forget that it would be worth leaving the approved mods on the board to create the memory hole and remove the SCIOS images...

Re: I found it! A very sorry looking MK14.
 

Obviously the top will be harder to get a clear view of

Re: I found it! A very sorry looking MK14.
 

Unfortunately it's the top I'm having the most trouble with !.

I've cut so many tracks around ICs 16 & 17 it's difficult to see what they were originally. I'll probably have to use the circuit diagram to work it out.

Regarding the 'official mods', I'm not sure if I did them as per the instructions posted in this thread.

These are the instuctions I followed, from the 'Instructions for Revised Monitor' leaflet. There is no mention of swapping C6, and mine is still in it's original postion. These instructions applied to the Single-Step, and are described as resolving a conflict between ROM data and status during NADS.

I'm not too bothered about the duplicated ROMs anyway. Micky is not going to be used for any further experiments, I've got Vicky for that.

Cheers,

Buzby

Re: I found it! A very sorry looking MK14.
 

That mod is for the addition of the single-step feature (as you have said) because the revised / new OS has the support firmware for it built in. The memory hole mod may coincidentally have needed similar mods. If you don't fit the SS hardware but you do fit the 'new' OS, you need to take SENSE-A to 0V otherwise programs will not run.

Right back at the beginning of Slothie's epic 'Schematic Revisions' thread I posted the instructions SOC sent to me when I enquired about how to add extra memory - they don't explain how to add extra memory but they do explain how to free up the memory hole. Not sure if it has also been posted in this thread, if so I could not find it.

https://vintage-radio.net/forum/show...13&postcount=6

Problem is they only explain it from a practical / hardware level (cut this, join that) rather than at circuit diagram level, so I can't say whether the IC pin numbers referred to are correct for an issue II PCB. I actually never did the mod, instead, I removed the VDU which was chewing up nearly all of my memory and didn't use it again until Slothie's issue VI PCB rode to its rescue.

Agghh, just noticed Tim reposted it a few moments ago.

Re: I found it! A very sorry looking MK14.
 

I do have an actual issue II here of course - I'm not going to be removing anything from the PCB at this stage in its life but happy to follow or buzz out any connections you may need to know about. - It's in storage at the moment though so would have to wait until tomorrow now.

Re: I found it! A very sorry looking MK14.
 

I think I duplicated the required gate arrangement using new gates on the daughter board, not re-using chips on the main board. This would mean I didn't need to make the reset switch mod.

Looking at my notes the new memory map was :

0700 Extra RAM on daughter board
0600 Extra RAM on daughter board
0500 Extra RAM on daughter board
0400 Extra RAM on daughter board
0300 'OLD' ROM on daughter board
0200 'OLD' ROM on daughter board
0100 ROM on main board
0000 ROM on main board

( It looks like I made no changes from 0800 upwards, well, not intentionally !. )

Cheers,

Buzby

Re: I found it! A very sorry looking MK14.
 

What was the rationale behind having the old OS at 0200-03FF, do you remember? I had imagined you must have had them both mapped at 0000-01FF with the chip enables switched either-or in some way.

Re: I found it! A very sorry looking MK14.
 

The idea was that I would use the 'old' ROMs to check the circuit worked, then replace them with custom ROMs at some time in the future, but that never happened !.

Re: I found it! A very sorry looking MK14.
 

You've never mentioned having the official PROM programmer, I've never come across anyone who did - it must be one of the rarest items of original MK14 hardware around.

Ironically I do now possess both a capable programmer and a small stash of MK14 compatible PROMs, but even now I can't think of any application which I really need to commit to PROM. I think the other idea you implemented, battery backed RAM, must have made the need for custom PROMs more or less redundant. That's one mod which probably would be worth reinstating eventually.

Re: I found it! A very sorry looking MK14.
 

I never mention the official PROM programmer, 'cos I never had one !,

By the time I'd got round to programming EPROMS I'd left Micky behind, and moved onto ZX81.

( I built an ultra-simple programmer for the ZX, I just wish I'd kept that as well. )

Re: I found it! A very sorry looking MK14.
 

Back to Micky.

I know SoC didn't put pin numbers on their circuit diagram, but did they also scramble the ABCD notation of gates in a package ?.

Just checking address lines A8 and A11 to IC 16.

On the board A8 is to pin 13, A11 to pin 12. SoC have shown these as inputs to gate A.

Usually these pins are labeled belonging to gate D.

SoC are not making it easy !

Re: I found it! A very sorry looking MK14.
 

If you feel like re-drawing the circuit diagram of the issue II the way it really is with a modern circuit diagram package, I for one would find that useful. Maybe you could start with Slothie's issue VI and roll it back to issue II.

It would be interesting to know what proportion of the total output of MK14s were issue II, III, IV, V respectively. I don't count issues 0 or 1 as I have never seen one.

Issues II, IV and V each seem to have had respectable runs, issue III not so much.

Re: I found it! A very sorry looking MK14.
 

Well it's normal convention to letter-label gates in ascending pins used order. But it does seem SoC have just assigned letters from top to bottom on (Iss.4? / 5? at least) schematic, that does have pin numbers (unlike earlier 'Remove from Book' Issue 1? / 2? one in the V1 manual).
I've not found any other versions on the 'net so far (But I presume SoC wouldn't have changed the connections of the existing circuit unnecessarily, and just added the odd extra).

And it seems SoC had chosen which gate to use on PCB connections, based on what made tracking to it easier, so often made their schematics difficult to tie-up with the PCB if they weren't clear with actual pin numbers and standard labels.


Chris Oddy's replica (based on Issue 5, with PCB tracking kept as close to original as possible), schematic also has A8 is to pin 13, A11 to pin 12 on IC16 - which he's labelled IC16.4, seemingly using ICxx.(1-4) to avoid confusion with SoC's letter allocations:
http://theoddys.com/acorn/Replica%20...0Schematic.pdf

Re: I found it! A very sorry looking MK14.
 

When I was working out a schematic for my replica I came to the conclusion that SoC's schematics where more of a general guide than an actual representation of the circuit.

Re: I found it! A very sorry looking MK14.
 

A few people now have re-drawn the MK14 (although mainly latest versions) on a modern CAD system, to make it more readable. With people like Chris Oddy trying to keep it looking the same as the original, with all the same designators as well as overall style of the schematic - but sometimes with some extra labels to make it clearer.
So could probably edit one of these, to make older versions. However it does seem that it's not very clear how many version did actually exist originally / what version they actually were, if PCB (and schematic) wasn't labelled with this.
I've only found two versions of the schematic on the 'net so far, and later one is rather confusing in notes that say spare gates are only used on issue V, but they don't connect them, so possibly indicating it is only for previous issue 4.
The other main one is from the V1 manual, so might have presumed that was Issue 1.

Then there is the issue that there seems to be uncertainty on how many in total were actually made. This: https://en.wikipedia.org/wiki/MK14
gives either 15,000 or a rather high 50,000 (half that of the ZX80)
Although ZX80's seem to be about as rare (I've only got the PCB from one, that someone has sawn the keyboard part off!) , compared to the 1.5m made ZX81's which were commonplace - I've got quite a few, and still often see others for sale at rallies etc.)

What would be very useful, is a list of all the exact changes between the various issues of schematic / PCB - I've not seen a definitive list, so far.

Re: I found it! A very sorry looking MK14.
 

I'm surprised no-one seems to have done a replica of the PROM-Programmer, if they are even rarer than original MK14's itself.
There wasn't too much to one / hadn't cost too much, from original photo of one in advert here: http://theoddys.com/acorn/Acorn%20Sy...4%20Advert.jpg

And there is a copy of the manual for it, here: http://theoddys.com/acorn/Acorn%20Sy...M%20Blower.pdf

Although it would be nice to have a detailed dimensioned photo of PCB with tracking etc.

However, as it only programs relatively expensive & getting rare and one-time fusible-link PROM's, then one that also did EPROM's (like Acorn System one, that came from the same original MK14 designer?) and a converter for these back to PROM sockets might be more useful.

Re: I found it! A very sorry looking MK14.
 

MK14 Man has an original (photo attached) and Martin Lukasec did a repro Board - I have all the components to build one here but, as yet no board. As you say a bit of a curiosity due to the difficulty of getting the 571 PROMS.

Re: I found it! A very sorry looking MK14.
 

As regards the versions - this is the best images of Issue 3 I have located so far from keeping an eye on very blurred bay sales... I had an issue 4 from the same source but, a friend has an original and is looking at getting a better scan from the badly damaged image he has.

Re: I found it! A very sorry looking MK14.
 

In fact scratch that we should switch to the Versions thread as I have just found a mislabeled one that seems to be the same as the blurred one - no idea on source my note taking was poor at the start.

Re: I found it! A very sorry looking MK14.
 

Thanks for info - particularly the good top-side photo.

I see the repro one has double-side tracking, with quite a bit each side. Whereas the original one only has a few top-side wire-links.
So I would have thought that it would have been easier to go for a single-sided PCB that was originally used for minimal cost / could probably do one at home without the silkscreen - especially if there's a photo if the original PCB's underside tracking (although should be able to work out something similar, from component positions)

I recall seeing VDU boards being around (and info for a replica one?)

But I've not seen much about the cassette interface. It's simply enough to knock-up on a bit of veroboard, but would be nice to have somethng a bit closer to the original, so any details on these would be useful).

Re: I found it! A very sorry looking MK14.
 

Again Martin's site is the source of the VDU - here is a link to one of the articles with his repro Issue II - be careful to read as he ended up doing an Issue V but the top side picture may be useful.

https://www.8bity.cz/replika-mk14/ja...sinclair-mk14/

There is an English flag on the right had side which is pretty good translation.

The cassette interface page is harder to find as it is not on the index:

https://www.8bity.cz/2018/science-of...rface-replica/

The documents above are from 2015 in his blog that cover the early work on main board, VDU, cassette and programmer:

https://www.8bity.cz/2015/sinclair-s...om-programmer/

Re: I found it! A very sorry looking MK14.
 

You only have to ask .....

Re: I found it! A very sorry looking MK14.
 

Thanks - That 'Remove from Book' one, with 'Issue 3' hand-written on it, looks at first glance to be the same as one I already had found elsewhere and had come from 'V1' manual so I'd thought to be an earlier version.

One scanned-version I have, has IC12 & IC13 part numbers and function hand-written on it and I think I may have printed from a scanned V1 Manual, as another I found with blue pen writing of some IC types on it, is rather low-resolution (might have been due to site like this compressing it)
There is a version of just the schematic, amongst the many bits of canned info you can view here: http://www.computinghistory.org.uk/d...otype-of-MK14/
(But that copy has some punched-holes at the top)

Chris Oddy only refers to the 2 he has as early and later, here:
http://theoddys.com/acorn/Acorn%20Sy...Mk14/mk14.html
- Although it seems the links are currently broken, so I will let him know.