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Old 26th Nov 2022, 6:33 pm   #41
SiriusHardware
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Default 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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Old 27th Nov 2022, 10:17 pm   #42
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Default 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.
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Old 27th Nov 2022, 10:39 pm   #43
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Default Re: Idiot building a MK14 thread

Quote:
Originally Posted by ScottishColin View Post
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.
This is similar to the one I bought although I think mine is 40v for some reason..
Search for 1000uf axial electrolytic.

https://uk.farnell.com/illinois-capa...1000uf%20axial
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Old 27th Nov 2022, 10:53 pm   #44
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Default Re: Idiot building a MK14 thread

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Originally Posted by ScottishColin View Post
>>
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?
>>

Colin.
I presume this is the Electrolytic capacitor, in which case you probably need to search for an axial (Horizontal PCB-mount, with leads out of the opposite ends) rather than radial (vertical PCB-mount , with both leads out of the same end).
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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Old 28th Nov 2022, 12:06 am   #45
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Default 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.
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Old 28th Nov 2022, 12:51 am   #46
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Default 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:
Originally Posted by SiriusHardware View Post
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.
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Old 28th Nov 2022, 1:49 am   #47
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Default 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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Old 5th Dec 2022, 9:34 pm   #48
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Default 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.
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Old 5th Dec 2022, 10:49 pm   #49
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Originally Posted by SiriusHardware View Post
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.
Oh I'm glad you've managed to get one made, I have been wanting to send you one for almost the last year but I haven't been able to arrange it what with one thing and another, and the post office near here seems to be permanently closed. I was reasonably sure it would fit the keys as I have a set of the caps that I think you have and tried them out.
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Old 5th Dec 2022, 11:09 pm   #50
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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.
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Old 8th Dec 2022, 12:18 am   #51
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I once saw an MK14 built quite neatly into what had obviously once been a wooden box for a chess set or backgammon set - two identical shallow rectangular wooden trays hinged together at one long side with a brass catch at the opening side to keep the lid closed in storage or transit. That is typical of what went on back in the day, given that there was no 'official' casing / enclosure available.
I've just spotted an MK14 + Memory-expansion in a wooden box (presumably put in it a long time ago) in the CfCH Collection:
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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Old 9th Feb 2023, 7:31 pm   #52
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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.
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Old 9th Feb 2023, 10:20 pm   #53
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Thats good news, hopefully Colin has time to build his MK14 soon.
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Old 11th Feb 2023, 3:57 pm   #54
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I’ve changed to using standard sockets for most of my builds using older components. The problem I have with turned pin sockets is that they grip the pins of the IC tighter than the standard sockets, so the first few removals of the old component from a new socket can stress the pin of a difficult to replace component. After about five or six removals the turned pin socket doesn’t grip the component any tighter than a standard socket and I think when you get to ten removals they are weaker grip than the standard sockets.

By standard sockets I don’t mean the old texas instruments type that contact the edges of the pins, but the now common type that contact the inside and outside face of the pin.
I am with you here with the 'standard' sockets you are describing here I have not had any problems, while with turned pin I have lost pins from ICs - not great if it is one on the PROM chips or an expensive old 40pin device
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Old 11th Feb 2023, 4:22 pm   #55
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Default 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.
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Old 11th Feb 2023, 10:26 pm   #56
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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.
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Old 20th Feb 2023, 8:43 pm   #57
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Default Re: Idiot building a MK14 thread

Right. We're (finally) starting. Sockets first.

Colin.
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Old 20th Feb 2023, 9:00 pm   #58
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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.
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Old 20th Feb 2023, 9:56 pm   #59
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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.
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Old 21st Feb 2023, 6:05 pm   #60
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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.
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