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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
GrahamN
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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
SiriusHardware
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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
GrahamN
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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
GrahamN
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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
SiriusHardware
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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
GrahamN
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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
SiriusHardware
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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
GrahamN
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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
JimmyDeath
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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

James
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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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