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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 3rd Sep 2020, 6:37 pm   #1
Buzby123
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Default I found it !. A very sorry looking MK14

Deep in a long lost corner of my attic, I found my MK14.

Time has not been kind to it, and it looks like I was not so kind to it either, back in the day.

I can recognise the cassette interface, and the board I built to drive the new display.

The board near the cassette interface looks a bit like a D-to-A resistor network, and it has a pair of wires to two ( of the many ) unlabelled sockets on the front.

I've no idea what the battery-backed circuit is for. It's got two NMC6514 1k x 4 RAM chips on it, so maybe I had a non-volatile RAM somewhere in the memory map.

The display board is from 'Sintel' ( who remembers them ? ) with 8 FND507 LEDs, I think.

The MK14 itself is an Issue 2 board, so that explains all the wiring on the back. The chopped-off ribbon was to my VDU sprite board, long gone now.

The three un-marked switches need some tracing. One is probably 'single step'. but I've no idea what the others are.

As you will notice, there are two mains transformers - because you can never have enough uninsulated 240v connections in your aluminium enclosure.

Am I going to plug it in ?. No way !.

The case is full of a white powdery substance, and it's got everywhere. I'm going to photograph everything, then take the boards out, clean up the white stuff, and then start on the MK14 board alone.

I've got plenty of spare parts, but not a lot of time just yet. It's going to be a while before Micky sings again !.

Cheers,

Buzby
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Old 3rd Sep 2020, 6:54 pm   #2
SiriusHardware
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Default Re: I found it !. A very sorry looking MK14

That looks like a really good 'real life' MK14, very typical of the sort of things which would have been done back then. I bet it looked really smart when it was all fresh and new.

For a long time mine (also issue II) had the display and keypad extended off board and it was fitted in various enclosures, the neatest of which was an executive-style briefcase complete with a set of 'D' batteries which would run it for a few hours.

In the noughties I embarked on a process of restoring it to more or less original single-board configuration, although the original keypad was long gone by then.
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Old 3rd Sep 2020, 7:36 pm   #3
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Default Re: I found it !. A very sorry looking MK14

I'm thinking the white powder may be fallout from the NiCad? NiMH? rechargeable battery.

I would get rid of, or at least replace that at the earliest opportunity, as we have seen terrible damage wreaked upon otherwise well preserved systems - not MK14s, but other retro systems like the Amiga A500, by decomposing rechargeable batteries.

I have a 'Maplin Z80 system' which had been in beautiful condition, but the PCB mounted NiMH battery started to out-gas some sort of vapour while it was in storage: A lot of the IC pins turned malachite green and the pristine white screen printing just drifted off the PCB like confetti when I tried to blow the white 'snow' off the PCB.
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Old 3rd Sep 2020, 7:40 pm   #4
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Default Re: I found it !. A very sorry looking MK14

Quote:
Originally Posted by SiriusHardware View Post
That looks like a really good 'real life' MK14 ...
Yes, this one had a really good life !.

It's had just about every gadget under the sun plugged into that breadboard, and the main board has been modified no end.

It even had a role in factory life !.

We were installing PLCs in a synthetic fibre plant. We had been told the fast IO cards we needed were on 6 weeks delivery, but it was really 6 months.

To get the plant running in time, I programmed the MK14 to take the fast signals from the plant, and replay them to the PLC a a slower rate.

This is the machine I cut my programming teeth on, and it was fun !.

Very soon after I moved on to Acorn System 1, then Apple ][, and they were fun as well.

Now I've got Arduinos and rPis, but no inclination to do anything with them.

Cheers,

Buzby
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Old 3rd Sep 2020, 7:50 pm   #5
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Default Re: I found it !. A very sorry looking MK14

It has been argued here that the MK14 was really the Arduino of its day - although it never had 'Flash memory' as such, you could buy the optional PROM programmer and burn project-specific firmware for it so that it would instantly do that job as soon as it was turned on, much like an Arduino which has been programmed with a 'sketch'. Yours of course had (rather rare) nonvolatile program storage so yours could have been used in a more Arduino-like fashion than most.

I've heard of one case (only) where MK14s were apparently used as dedicated controllers in stage / venue lighting equipment, but unfortunately I don't have the name of that specific product. There may be a few 'embedded' MK14s still around awaiting to be discovered in the back rooms of old clubs or theatres.

The Pi and Arduino both provide handy ways of 'typing' code into the MK14 at fairly high speed, so they have their uses.
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Old 3rd Sep 2020, 7:53 pm   #6
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Default Re: I found it !. A very sorry looking MK14

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Originally Posted by SiriusHardware View Post
I'm thinking the white powder may be fallout from the NiCad? NiMH? rechargeable battery.
No, and yes.

The battery is NiCad, and it is going a bit green, but the white stuff I think is something completely different - concrete effloresence. ( Don't ask ! )

Cleaning this up is going to be my first task. ( If I took the MK14 out and did that first, I would think 'Job Done', and it would never get back in its box again. )

Cheers,

Buzby
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Old 3rd Sep 2020, 8:02 pm   #7
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Default Re: I found it !. A very sorry looking MK14

We look forward to seeing the end result, as and when you have to time to get to it of course.
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Old 4th Sep 2020, 9:14 am   #8
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Default Re: I found it !. A very sorry looking MK14

I'd love to know what that sheet music is....
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Old 4th Sep 2020, 9:24 am   #9
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Default Re: I found it !. A very sorry looking MK14

It looks like I was trying to get Micky to play Cwm Rhondda.
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Old 4th Sep 2020, 9:41 am   #10
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Default Re: I found it !. A very sorry looking MK14

That tune appears polyphonic (more than one note at a time) so good luck with that! Although, there were some games for the Spectrum which managed polyphony over the Spectrum's single digital audio output - 'Fairlight' springs to mind.

I have toyed with the idea of adapting 'Music Box' to play its output over MIDI, since I have several MIDI equipped synths here. The original tune in the manual is 'God Save The Queen'. I think that would sound quite good on distorted electric guitar, Hendrix style.

Who will write the first MK14 'tracker'?
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Old 4th Sep 2020, 5:43 pm   #11
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Default Re: I found it !. A very sorry looking MK14

That is a wonderful looking machine - as you say it cries out to be restored 'as is' . If it was mine I suppose the only 'mod' I would make would be to cut and fit a perspex window and white LED lighting to show off that lovely White CERAMIC SC/MP and reveal part of the cleaned up MK14... - very unusual.

Thanks for sharing and look forward to see the cleaned up result. As Sirius says a small hidden PI0W would allow it to be used for wireless uploading of programs easily using his programmer which could just be wired in parallel with the MK14 at no risk as it uses Opto Isolators.
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Old 4th Sep 2020, 6:31 pm   #12
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Default Re: I found it !. A very sorry looking MK14

I just dragged this one out of the bungalow I don't recognise the knitting so it might be one I acquired on the way as far as I remember mine ended up as a EPROM programmer and it's not turned up yet!

Cheers

Mike T
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Old 4th Sep 2020, 6:48 pm   #13
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Default Re: I found it !. A very sorry looking MK14

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Originally Posted by Cobaltblue View Post
I just dragged this one out of the bungalow I don't recognise the knitting so it might be one I acquired on the way as far as I remember mine ended up as a EPROM programmer and it's not turned up yet!

Cheers

Mike T
Nice one - full memory and an 8154... thanks for sharing and nice to know there are other MK14 owners/users around here.
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Old 4th Sep 2020, 6:55 pm   #14
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Default Re: I found it !. A very sorry looking MK14

Cobaltblue (and Coolsnaz2, who posted in the VDU thread) are both very fortunate to have genuine examples in such good original condition with the keypads still intact, as the original keypads were so 'eccentric' that they were usually replaced with something better as soon as possible.
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Old 4th Sep 2020, 8:36 pm   #15
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Default Re: I found it !. A very sorry looking MK14

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... the original keypads were so 'eccentric' that they were usually replaced with something better as soon as possible.
'Eccentric', that's a very diplomatic way of saying 'total crap'.

As an aside, I have another computer with a non-original keyboard ....
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Old 4th Sep 2020, 11:38 pm   #16
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Default Re: I found it !. A very sorry looking MK14

I've unplugged the daughter board, just to see it a bit better.

It looks like my Micky needs this board to run. IC16 on the main board has been removed, and some pins on two of the 2111s have been bent up and wired to the daughter board. I think there is a lot of address decoding which is now on the daughter board.

Also, there are two 74S571 chips on this board, and two still on the main board.

It's coming back to me through the mists of time, I think the toggle switch near the red button would let me select 'old' or 'new' ROMs. ( Don't ask me why I thought this was a good idea, it was a long time ago. )

This is one seriously hacked MK14, I must have been really enthused to have put so much effort into it.

One thing I am missing is documentation. ( I might find it, but I'm not holding my breath. )

Does anyone have a link to an Issue 2 schematic ?.

Cheers,

Buzby
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Old 4th Sep 2020, 11:53 pm   #17
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Default Re: I found it !. A very sorry looking MK14

I have never seen an Issue 2 diagram anywhere online - I have a very grainy lo res Issue 4 captured from an e-bay listing and one I do not know that just says "originalSchematic.jpg" which I think is Issue 3 a slightly fuzzy version is at: https://www.old-computers.com/museum...Diagram_s1.jpg
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Old 5th Sep 2020, 9:49 am   #18
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Default Re: I found it !. A very sorry looking MK14

I still have all the original documentation which came with my issue I I but you've caught me at a bad time as I am away from Tracy Island just now. The most widespread diagram online is that of the issue II as far as I know, it was always much harder to find the one for the issue V.

If you haven't found it in a week or so remind me and I will scan mine.

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Old 5th Sep 2020, 4:08 pm   #19
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Default Re: I found it !. A very sorry looking MK14

This is a link to a copy of the MK14 manual for early versions of the MK14 including the schematic. It documents the "original" monitor that resets to "---- --" as well as the schematic showing the PROM decoded only by the A11 signal, as was the case with early boards.

https://drive.google.com/file/d/1C32...ew?usp=sharing

I'm pretty sure I've got the sharing options correct....!
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Old 5th Sep 2020, 8:46 pm   #20
Buzby123
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Default Re: I found it !. A very sorry looking MK14

Thanks for the manual, it's brought back a lot of memories.

Tomorrow I'm starting to fettle the case.

First I need to photograph every connection, as already a couple of wires have come loose.

Then de-solder and remove the transformers ( Still can't remember why I've got two transformers. I think the second one is for a +ve and -ve supply to a 741 op amp. )

Then remove all the circuits from the bottom and sides. Then I can give it a good wash.

That big electrolytic is dated 1974, will it need replacing ?.

Cheers,

Buzby
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