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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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26th Nov 2022, 6:33 pm | #41 |
Dekatron
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Location: Newcastle, Tyne and Wear, UK.
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Re: Idiot building a MK14 thread
I noticed someone in Croatia asking him for copies of the scans and I wonder if that is how the Czech replicas eventually came to be. A reminder, Tim has an unbuilt and as yet unscanned Czech replica PCB.
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27th Nov 2022, 10:17 pm | #42 |
Octode
Join Date: May 2012
Location: Perth, Scotland
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Re: Idiot building a MK14 thread
I'm still collecting parts and waiting for the postie right now. I intend to build in the last couple of weeks of December as I have some time off and work is a bit busy right now.
I can't find a suitable version of the larger capacitor with the legs in the right place (C2) - can someone point me at that please online? I have 3D printed a camera holder for my ripod to fit my mobile phone in to video what happens - I intend to video the build; I'm not sure how interesting or useful it'll be but I'll give it a go. Thanks. Colin. |
27th Nov 2022, 10:39 pm | #43 | |
Octode
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Location: Newbury, Berkshire, UK.
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Re: Idiot building a MK14 thread
Quote:
Search for 1000uf axial electrolytic. https://uk.farnell.com/illinois-capa...1000uf%20axial |
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27th Nov 2022, 10:53 pm | #44 | |
Octode
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Location: Northampton, Northamptonshire, UK.
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Re: Idiot building a MK14 thread
Quote:
Although it is possible to mount either the other way round, by extending one lead across the case to the other end (and manufacturers sometimes did this). You will probably find that modern ones are rather smaller than the original one, but leads may still be long enough to reach / could be extended a bit. The value isn't that critical, so could use a slightly higher one / higher voltage, if that helps in getting a more similar size one. Equally, a lower value shouldn't be an issue, as this capacitor seems to have been for operation from an unsmoothed (just rectified-AC) DC-supply. Whereas if you are operating it from a decent regulated-DC PSU, it probably doesn't really do much / not really needed. The MK14's original decoupling was exceedingly minimal / in odd places, and it probably only worked as it operated at a relatively-low frequency. But I believe some of the later replica PCB have enhanced the decoupling. |
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28th Nov 2022, 12:06 am | #45 |
Dekatron
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Location: Newcastle, Tyne and Wear, UK.
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Re: Idiot building a MK14 thread
Slothie's issue VI has an easy to remember 14 100n decoupling capacitors as it was observed that the decoupling on original MK14 PCBs was minimal.
Colin, I included a link to a potential part for C2 in a PM to you but perhaps those particular ones have gone? I don't know if this is obvious, but you don't need to find an axial capacitor with a body exactly the same length as the distance between the holes, the body can be way shorter - new / old stock ones always have long leads, and you just crank the leads downwards at the right distance from each end of the body. As long as the length of the capacitor body is not LONGER than the distance between the solder pads it will be OK. Last edited by SiriusHardware; 28th Nov 2022 at 12:11 am. |
28th Nov 2022, 12:51 am | #46 | |
Octode
Join Date: May 2012
Location: Perth, Scotland
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Re: Idiot building a MK14 thread
Apologies - I've just re-read your message and found the link. I have ordered from there.
Colin. Quote:
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28th Nov 2022, 1:49 am | #47 |
Octode
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
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Re: Idiot building a MK14 thread
You could just 3d print a dummy capacitor, I don’t think its needed with any modern power supply.
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5th Dec 2022, 9:34 pm | #48 |
Dekatron
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Re: Idiot building a MK14 thread
Speaking of 3D printing, Colin has just very kindly sent me a couple of samples of Slothie's Issue VI keypad frame (designed to fit over / around tact switches with snap on covers) - very very nice, I have to say. Thanks to Slothie for the design and Colin for the execution. It's the final finishing touch to my issue VI.
I just need to find some black machine screws of the exact right length - I may have some at work, so I'll have a bit of a root around there tomorrow. Last edited by SiriusHardware; 5th Dec 2022 at 9:41 pm. |
5th Dec 2022, 10:49 pm | #49 | |
Octode
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Re: Idiot building a MK14 thread
Quote:
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5th Dec 2022, 11:09 pm | #50 |
Dekatron
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Re: Idiot building a MK14 thread
Yes, It's an excellent fit, the cutouts are just close enough to stop the keys from rotating or tilting but loose enough to let the keys move as they should. Just the addition of that one 'custom' part makes the machine look really smart, like a manufactured product. Highly recommended for anyone thinking of going the keytops + snap-on clear covers route rather than using an overall overlay type.
I confess I prefer keys which move freely and independently rather than switches being pressed on by an overall membrane. The upside of the overall membrane type is that the overlay comes fully legended, whereas with the keycaps + key covers method you have to cut out and insert all of the key legends individually, which takes a bit of patience. Thanks for posting the files (which of course I do not have the means to use) and so thanks again to Colin for printing them. |
8th Dec 2022, 12:18 am | #51 | |
Octode
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Location: Northampton, Northamptonshire, UK.
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Re: Idiot building a MK14 thread
Quote:
http://www.computinghistory.org.uk/d...n-wooden-case/ I also see that the kit came in a folding sides cardboard-box, that it may have been possible to operate it in (maybe best to not leave it running unattended if it did get quite hot in places...): http://www.computinghistory.org.uk/d...-Original-Kit/ It looks like the prototype stripboard one, pictured here, was actually smaller (although lacking the keypad etc): http://www.computinghistory.org.uk/d...otype-of-MK14/ |
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9th Feb 2023, 7:31 pm | #52 |
Dekatron
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Re: Idiot building a MK14 thread
Just to bring this thread a little bit more on track, Colin's PROMs for his MK14 replica build arrived here and after a minor catastrophe involving the failure of the DOS laptop I normally use for this job, I found another suitable machine at work and installed my programmer's 'front panel' software on it.
I'm pleased to say (and Mark1960, who kindly gave the N82S131N PROMs to Colin, will be pleased to know) that the PROMs were genuine blanks and I had no trouble programming them. So Mark, you can go ahead and build that 82S PROM programmer now. Attached at the bottom, a pic of my Issue VI running a short program with Colin's PROMs installed and its normal DM74S571s sitting next to the machine. I'll put them back in the post to Colin some time in the next few days. The program to display a fixed message is quite short and easily typed in as an initial test of the machine once it's built, here is the code 0F20-C4 0F21-0D 0F22-35 0F23-C4 0F24-00 0F25-31 0F26-C4 0F27-0F 0F28-36 0F29-C4 0F2A-3B 0F2B-32 0F2C-C4 0F2D-07 0F2E-01 0F2F-C2 0F30-80 0F31-C9 0F32-80 0F33-C4 0F34-FF 0F35-02 0F36-70 0F37-94 0F38-F5 0F39-90 0F3A-F1 0F3B-00 0F3C 6D 0F3D 02 0F3E 37 0F3F-06 0F40-38 0F41-3F 0F42-39 The bytes from 0F3B to 0F42 contain the seven-segment codes which make up the displayed characters, so you can have fun trying to get it to display other things - it's a good way to get to understand the relationship between the bits in the data and the segments which are lit. For 'technical reasons' the characters are stored in reverse order, so the data for the leftmost display cell is in address 0F42 and the data for the rightmost display cell is in address 0F3B. |
9th Feb 2023, 10:20 pm | #53 |
Octode
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
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Re: Idiot building a MK14 thread
Thats good news, hopefully Colin has time to build his MK14 soon.
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11th Feb 2023, 3:57 pm | #54 | |
Pentode
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Re: Idiot building a MK14 thread
Quote:
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11th Feb 2023, 4:22 pm | #55 |
Octode
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Location: Northampton, Northamptonshire, UK.
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Re: Idiot building a MK14 thread
I've not encountered turned-pin sockets pulling the leg off an IC so far.
But alignment of pins can be more-critical with turned-pin ones, so probably even more important to pre-bend each side against a flat surface of any never-used IC's (from their default splayed-out - that was to ensure when used with auto-insertion machines they were spring into alignment / held tight into PCB's whilst soldering). So I have sometimes had a leg bend under at 90 degrees, if it didn't exactly line-up with the centre of a turned-pin, that did need careful straightening again. Most legs do survive this a few times, but if stored in some old conductive foam over a long-period, then that can often attack the metal with the dreaded 'leg-rot' Fortunately, if the shoulder of the leg is still OK, then can usually graft a replacement leg onto that by soldering a bit of suitable gauge tinned copper wire and trimming to length of others. If the shoulder has snapped-off as well, then it's also possible to drill into the side of plastic-packages a bit, to expose enough of the internal lead-frame metal to solder something onto. - Although the IC's then not totally-original looking, it's probably still worth doing to save an expensive one. Another way is to fit broken-legs IC into another socket, and drop solder down places where pins have gone. Using another socket, under an expensive IC, can also be useful as a 'pin-saver', if it is likely to be removed and re-inserted a bit. Also, if using originally soldered-in 'pulls', then I normally remove all solder with desolder-braid, squeeze pins completely flat, and use a fine flat needle file across each side to ensure all pins are smooth and no slight bits of solder to catch in sockets and cause damage upon any future removal. |
11th Feb 2023, 10:26 pm | #56 |
Dekatron
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Re: Idiot building a MK14 thread
We're making this all sound frighteningly difficult, although I remember Colin already had some problems with pins falling off ICs during his epic PET saga and he managed to tough his way through all of that.
I think all the ICs he's going to be using for the MK14 build are new or new-old-stock, but still, my suggestion would be to use 'standard' sockets for the reasons outlined above. On the other hand if turned-pin sockets are the only ones available, use those. The PCB is a proven design so all that needs to happen is for all the ICs to go in the right places the right way around first time. With the possible exception of the PROMs there should be no need to remove them again once fitted. |
20th Feb 2023, 8:43 pm | #57 |
Octode
Join Date: May 2012
Location: Perth, Scotland
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Re: Idiot building a MK14 thread
Right. We're (finally) starting. Sockets first.
Colin. |
20th Feb 2023, 9:00 pm | #58 |
Dekatron
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Re: Idiot building a MK14 thread
Good man.
If you are using IM6561 type RAM, don't forget to look at the 2111 / 6561 memory type selection link on the underside of the PCB - if you are using 6561 types, cut the nearly invisible '2111' link and solder-blob the 6561 link. |
20th Feb 2023, 9:56 pm | #59 |
Octode
Join Date: May 2012
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Re: Idiot building a MK14 thread
All sockets and resistors in. That'll do for tonight.
Random continuity tests seem ok - I'll do a fuller set tomorrow and check for any shorts. I've noticed a tiny error in the .PDF document - R16 isn't listed in the BOM. Colin. |
21st Feb 2023, 6:05 pm | #60 |
Dekatron
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Re: Idiot building a MK14 thread
Thanks for pointing that out - looking at a photo of the bare PCB I note that R16 like all the others has the value (4K7) screen printed next to it, but not having it in the BOM as well could lead to people failing to include it in their parts order.
One suggestion, when you have everything including the regulator but none of the ICs installed yet, is to power up the PCB like that and make sure your +5V coming out of the regulator really is +5V. If you do nothing else, at least do that and then power down again before fitting any of the ICs. Last edited by SiriusHardware; 21st Feb 2023 at 6:12 pm. |