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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 12th Mar 2018, 8:41 pm   #1
SiriusHardware
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Default Replica MK14 PCBs

I found this flagged up over on the vintage computer forums and thought it might also be of interest to some here.

Over the years the idea of reproduction Science Of Cambridge MK14s has been approached from various angles. There is, for example, Karen O's open-source PIC14 hardware MK14 emulator.

There was also a majorly redesigned MK14 'tribute' from 'MK14man' quite a while back, and there have been a couple of individuals who went down the road of trying to reproduce the original MK14 PCB, originally just to build their own replicas.

One of those individuals now seems to be producing replica MK14 PCBs in small batches and making them available for sale, see here.

http://www.8bity.cz/2018/final-repli...mk14-sinclair/

Unfortunately the translation from the original Czech is not too good, but the gist of it seems to be that he can supply PCBs, a remanufactured late version MK14 keypad and a pair of PROMs programmed with the 'SCIOS' monitor (either version) - finding the rest of the parts including the SC/MP processor and INS8154 I/O-RAM IC (if required) is up to you.

Last edited by SiriusHardware; 12th Mar 2018 at 8:50 pm.
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Old 26th Mar 2018, 9:51 pm   #2
SiriusHardware
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Default Re: Replica MK14 PCBs

Further to this, although it doesn't seem to have generated a great deal of excitement -

I've since found that in addition to the authentic looking Czech made replica PCBs mentioned in the first post, there is another company offering unpopulated replica MK14 PCBs.

(Seventh item down on this page)...

http://jmprecision.co.uk/shopping/st...=1&cat=17&=SID

Unlike the other ones, these are unashamedly modern in design, green, with solder resist and white screen printing on the upper surface. Only one side is shown so it's not clear whether the rear edge connector is single sided (as it was on MK14s up to about issue III) or double sided as it was on later issues.

This version also makes no provision for the fitting of a historically authentic keypad, but is laid out for modern keyswitches / contact switches. If you've ever used a real MK14 you'll know that isn't necessarily a bad thing.

The usual disclaimer: In neither case do I know the sellers, nor have I bought either of these products myself.
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Old 27th Mar 2018, 11:53 am   #3
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Default Re: Replica MK14 PCBs

Thanks for that - I'm quite tempted if I can find the processor at anything like a reasonable price. The jmprecision website, though, hides its owner, so I would be reluctant to purchase from them. The same boards are offered on eBay (maybe by the same person?) so a safer purchase if I decide to buy. I remember really wanting one of these when the originals were advertised, but was saving for a house deposit at the time so couldn't justify the cost. The only problem is the obsolete parts - I may just go for an emulator if I can't find them.
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Old 27th Mar 2018, 12:27 pm   #4
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Default Re: Replica MK14 PCBs

I know of one person over in the vintage computer forums who has actually ordered the JM version PCB but I don't know if he has received his yet.

To be honest they seem eye-wateringly expensive to me, more for the unpopulated board than the original 39.95 cost of an entire MK14 kit - although, of course, that was quite a bit of money in those days.
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Old 27th Mar 2018, 12:47 pm   #5
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Default Re: Replica MK14 PCBs

If I remember correctly the house deposit I was saving for was less than 1000 - 40 in 1977(?) is probably equivalent to 4 or 5 hundred pounds today, maybe more. I don't remember exactly but I'm sure I was on less than 15 week take-home before any living expenses.
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Old 27th Mar 2018, 12:48 pm   #6
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Default Re: Replica MK14 PCBs

It seems the CPU and RAM are still available at reasonable prices - it's the display that looks a bit tricky.
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Old 27th Mar 2018, 1:11 pm   #7
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Default Re: Replica MK14 PCBs

What you do there is buy a cheap, commonly available calculator from the same period - I have have found that the basic 'Texet 880' model has a pin-compatible display, a Nat Semi part exactly the same size and shape as the original MK14 display.

That's what I have used in my (still unfinished) Karen-O emulator - but I tested it on my original MK14 first. (Years ago, I installed a pin row connector on the MK14 PCB so that it was easy to disconnect the display and remote mount it if I felt the need, and that makes it easy to test other displays on it).

The display from an otherwise broken Sinclair /Thandar /RS PDM35 DMM or PFM200 frequency meter is also the same, although unfortunately the latter items themselves command fairly high prices now especially if they are Sinclair branded.
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Old 27th Mar 2018, 1:45 pm   #8
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Default Re: Replica MK14 PCBs

Thanks for that - just managed to pick up a working calculator for a fiver, so I'm going to start collecting the parts together to hopefully build something after my holiday.
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Old 27th Mar 2018, 6:32 pm   #9
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Default Re: Replica MK14 PCBs

If you get to the point where you need PROMs programmed for it (containing the operating sytem / monitor) drop me a PM as I have the code for both PROMs - for the revised / updated version of the monitor - in hex file format.

I also have a programmer which can programme those PROMs, should you need that done, although you would need to provide the actual PROMs as I don't have any spare. I think they - or pin-equivalent devices - are still not too hard to find.

Note they have to be 'new' never-used blanks as they are one-shot fusible-link PROMS. Second-hand / used ones can't be erased and reprogrammed.
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Old 27th Mar 2018, 8:06 pm   #10
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Default Re: Replica MK14 PCBs

I may well take you up on that - thanks

I'll do a bit more research into parts, and if it looks a goer will probably start putting something together in June or July.

I've been looking at a PIC emulator as well - may be interesting to build something like that as well.
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Old 3rd Apr 2018, 10:30 am   #11
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Default Re: Replica MK14 PCBs

Thanks for this, I had always considered making my own replica but never seem to have the time to do the PCB although I have over the years gathered all the ICs required. Don't really like the look of the JM version but am interested in the board in the first link which looks closer to the original.

Has anyone enquired as to the price of one of these?

Regards

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Old 3rd Apr 2018, 11:36 pm   #12
SiriusHardware
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Default Re: Replica MK14 PCBs

My preference (If I did not already own one) would be for the Czech-designed board which looks more authentically retro but it does not seem to have a stated price at the moment. It looks as though the originator is asking people to email him expressions of interest and the cost may go lower per unit if more people are interested.

Quote:
For the first batch of candidates I got registered, so all I e-mail. If you come, I'm sorry, let me know, I'll let you into a second dose.
If you are interested, I can only suggest you try emailing the Czech gentleman whose project it is to see if you can get on the waiting list for the second batch. I believe I have the correct email for him, I can PM it to you if you wish.

He's done some other things which are of just as much interest to owners of real MK14s, for example a replica of the original (optional) cassette tape interface for saving and loading programs to and from a tape recorder - also an Arduino based project which communicates with the tape data input / output streams from the MK14 at the TTL data level and is, as far as the MK14 knows, a cassette interface with a tape recorder connected to it.

The keypad he has had designed for his project consists of a professionally made stick-down durable sheet with the keys printed on it in the original style, and a set of metal dome contacts similar to the ones used in cheap late seventies / early eighties calculators. However, there is one important difference, the contacts he supplies have four points of contact with the PCB (when not pressed) and his PCB is laid out for those. An original late-issue MK14 was laid out for dome contacts with three 'feet'. If you wanted to use one of these new keypad sheets to restore the keypad on an original late-issue MK14 you could, but you would need to harvest a set of three-point contact domes from a cheap calculator from the same period.

He also appears to have made a replica of the optional VDU PCB as well, although this was easily the least useful add-on made for the MK14 because it didn't have any RAM of its own and took over 512 of the MK14's fully expanded memory of 600+ bytes, and the MK14 main board was never provided with a fully tracked address, data and control bus edge connection to connect the VDU to. I have an original MK14 VDU card but it has not been connected to my MK14 for more than 35 years.

The person I referred to earlier who had ordered a JM MK14 PCB has received his board and, last I heard, had it mostly populated. So they aren't just vapourware - at least one person managed to buy one.
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Old 11th Aug 2018, 6:14 pm   #13
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Default Re: Replica MK14 PCBs

I read some interesting (in as much as they were odd) comments on the JM board.
I am the creator of this and I have no idea why anyone would assume that they are 'vapourware'. They are offered and shipped within 2 days.
They have been designed as per the original design (edge connectors on just one side).
The JM website does not 'hide' me, it just does not give out my address as publishing personal details on an open web site is dangerous. There is however a contact form if anyone wants to contact me via the website (as many have).
The boards are also on ebay.
They were designed close to the original design except for where parts may have been hard to get hold of (such as switches) although I added things such as silk screen and solder mask to make it easier for builders to complete them without problems (I have no idea who may be purchasing these).
I created them (along with many other vintage boards) so that people such as myself that wanted to build a reasonably authentic MK14 had an opportunity.
Regarding price, I add 6.00 to the purchase price and so I do not consider this unreasonable considering the work in creating them.
I also do not think that comparing the current cost to the original kit price is a useful comparison but for completeness the current cost would have equated to 6.40 back when the MK14 was released and the board price back then was 9.30 so in real terms I sell them at a lower price that the originals and I must produce them in lower quantities.
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Old 12th Aug 2018, 12:36 pm   #14
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Default Re: Replica MK14 PCBs

Thanks for joining, and thanks for making your PCBs available. This was something which people had been hoping would happen for some time now, and we seem to have come to the point where all of a sudden, the availability of design tools combined with the availability of (relatively) cheap PCBs in small quantities has made this possible.

Going back through this thread, I believe I was the one who originally brought attention to the existence of your replica boards, and although I did later use the term 'vapourware' I used it in a sentence in which I said they were NOT vapourware because I knew someone who had ordered one. I think the issue only arose because there was originally something about your website - perhaps a lack of direct contact details - which made one of the other contributors wary of ordering from that source. Another contributor then pointed out that they could also be bought from you via another source which includes a form of payment protection.

Overall, I don't think this thread has been as negative about your replica boards as it may have seemed to you - as the originator, you would naturally be more sensitive to any implied criticism than most, but in fact there has been very little of that and we welcome the existence of your PCBs, and wish you every success with these and the other retro-replica computer boards you have, and are working on.
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Old 12th Aug 2018, 12:42 pm   #15
GrahamN
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Default Re: Replica MK14 PCBs

Just to add that I bought one of these boards, and it seems to me to be very good quality. I am just starting to put everything together, and hope to have a working board within the next few weeks.
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Old 21st Aug 2018, 8:35 pm   #16
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Default Re: Replica MK14 PCBs

I have just purchased a "Jerry" MK14 board and am happy with the price and sure that I will be with the board once it arrives. I remember saving all my Christmas money and pocket money to buy the board as a child and then it cost 40. It is now 40 odd years later and to be honest 40 is now nothing. I look forward to re-living my youth and rebuilding my MK14 on a decent PCB and maybe expanding or converting it using 39 years of knowledge and the wonderful internet. When I originally purchased, getting ANY information was impossible other than through the occasional magazine article (ETI and Elektor) and the fantastic book "Understanding Microprocessors with the MK14" which I purchased for 6.23 in 1980 with my student grant. Why isn't this book available as a PDF anywhere?
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Old 22nd Aug 2018, 11:27 pm   #17
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Default Re: Replica MK14 PCBs

A copy of that book came up on an auction site a while ago and I competed for it initially, but eventually I had to let it go as the price was getting out of hand. It eventually went for about 22.

The Centre For Computing History (Cambridge) appears to have a reference copy:-

http://www.computinghistory.org.uk/d...with-the-MK14/

My original MK14 manual is in dire condition, but I managed to buy a nearly spotless example for about 7 a few years ago - probably my lucky day.
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Old 23rd Aug 2018, 10:26 am   #18
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Default Re: Replica MK14 PCBs

Quote:
Originally Posted by SiriusHardware View Post
I know of one person over in the vintage computer forums who has actually ordered the JM version PCB but I don't know if he has received his yet.

To be honest they seem eye-wateringly expensive to me, more for the unpopulated board than the original 39.95 cost of an entire MK14 kit - although, of course, that was quite a bit of money in those days.
The mind plays tricks when it comes to the comparative value of money back in time and the older we are, the worse this phenomenon becomes.

The link below is as good a site as any for making historical comparisons of inflation, and works both ways. That is you can put a figure in today and find out what that would equate back in time to your chosen year, or you can put a figure in for your chosen historical year and it will tell you the equivalent in 2018. There are several indices which do this and may give different results, just as today there are several cost of living indices, but this one seems as good as any. I often use it for checking the price of vintage radios when updated to 2018:

http://inflation.iamkate.com/

As a matter of interest, the index shows that 39.95 in 1977 equates to 275. On that basis, the new PCBs at 37.00 - which look excellent quality, double sided PTH screen printed boards produced in small batches - seem remarkably cheap and would equate to 5.50 in 1977. I find it incredible and really quite uplifting that there are people who are so enthused and dedicated to this aspect of vintage technology as to design and source the PCBs for such a tiny niche market.

I recall that in 1985, I bought a Sinclair Spectrum 16k for 125, which equates to 505 today, and later upgraded it to 48k with a plug-in memory strip which cost 45 - the equivalent to 130 today. Think what 635 would buy today in terms of a laptop!

How times change!
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Old 23rd Aug 2018, 6:56 pm   #19
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Default Re: Replica MK14 PCBs

Absolutely, I said myself that 40 was 'a lot of money in those days'. But even allowing for inflation, rose tinted nostalgia, etc, 40 still seems like quite a lot of money for an unpopulated PCB of any sort today.

Contrast that with the boards made by Slothie, which were talked about in a related thread. I believe he said that he had self-designed and had made a number of replica MK14 PCBs, price - I can't remember if it was each, or for the whole lot - around 18. 20 ish seems like a more reasonable price to me for an unpopulated PCB.

However, what I can say is that I think Slothie subsequently found an error or two on his initial design, and that's what you're probably really paying for with the JM boards, the process of error elimination and development - or maybe just being really meticulous and getting it right first time.

One further point I've noticed about the JM boards is that they appear to be replicas of an early issue PCB - maybe issue II, whereas the Czech boards are issue V replicas. There are a areas where this may matter to a prospective purchaser. One is the matter of the top / rear edge connector. On early original boards and on the JM boards the PCB only has contact fingers on the upper side of the edge connector.

On late issue original PCBs this became double sided, and that was to make it easler to connect the MK14 VDU option in particular, as that required connections to the address, data and control buses which were not available on the edge connector.

Although Science of Cambridge never did track the lower side connections to anywhere useful, their presence made it much easier for the user to run links from the relevant points on the system to the lower side of the edge connector so that all connections required by the VDU could be picked up from the edge connector. There's an image here of an MK14 which has been modified to make use of the lower side contacts in exactly that way:-

https://www.flickr.com/photos/retrop...-7jBLdh-7jBz4y

The second reason anyone might prefer an issue V replica over issue II is that the address decoding seems to have been modified so that the unwanted images of the OS which originally occupied the address range 0200-07FF no longer did, making it potentially much easier to map a further 1.5K of external RAM into that address range.
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Old 24th Aug 2018, 12:09 am   #20
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Default Re: Replica MK14 PCBs

Interesting, I just checked and my original board is a ISS V board. So are there any details of the circuit actually used for this board?
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