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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 23rd Nov 2022, 10:06 am   #21
Timbucus
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Default Re: Idiot building a MK14 thread

Quote:
Originally Posted by Mark1960 View Post
Quote:
Originally Posted by Phil__G View Post
Many years ago Joe we used to buy just the actual metal sockets on a break-away strip,
no plastic surround, all metal - remember those? awful things, but cheap & cheerful
I did use those once, but never again. At least they are easy to remove.

Timbucus was looking for some recently to build a replica champ, not sure if he found any though.
No I am still looking if anyone finds some! I have a strip of about 10 only.
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Old 24th Nov 2022, 1:32 am   #22
ortek_service
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Default Re: Idiot building a MK14 thread

I also unfortunately only have probably around 10 somewhere - leftover, from when I once bought some to mount a non-standard (Compared to IC's) Dual-row 40way LCD above a 7106 DVM IC, on a bench DMM test equipment project.

Once I rediscovered what they were called and then found they were made by Molex in the vintage catalogue I found, I did do a quick search for 'Molex Soldercon', but couldn't find anyone selling these.
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Old 24th Nov 2022, 2:34 am   #23
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Default Re: Idiot building a MK14 thread

Im sure those "soldercon " strips were only two contacts.
Inside and outside the chip.
They came in huge rolls, like 500 in a full roll.

I "know " of them, I hate them and have never used them.

Joe

p.s. took me a while to remember.
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Old 24th Nov 2022, 11:54 am   #24
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Default Re: Idiot building a MK14 thread

I used to use Soldercon IC sockets back in the day, and I can't say I had any trouble with them, especially on double sided boards where the solder would come through and secure them on the top side. The only real failing was if they didn't have an IC in them they were somewhat liable to bend out of shape and could be tricky to bend back. But then I mostly used them on projects that were not destined for decades long lifetimes, just experiments or kits for home made test equipment that was going to be in a protective box.

These days I tend to use the twin-wipe type generally, or the turned pin ones in cases where I might want to make a plug-in "adaptor" such as a memory or IO device. Then you can use turned pin headers to make a reliable header - I find the twin wipe type tend to distort if you do this and are forever unable to grip an actual IC afterwards. Even worse if you use the square pin type headers.
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Old 24th Nov 2022, 7:21 pm   #25
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Default Re: Idiot building a MK14 thread

Pulling back onto the subject of Colin's build of Slothie's PCB, one of the items I sent up was a heatsink like the one fitted to mine. I posted a couple of pics elsewhere to show how it's fitted but I don't know if they were clear enough.

Image #1 is the heatsink viewed directly from the rear so you can see that the order of layers from from bottom to top is
-Screw head.
-Washer (metal on mine, but I sent Colin a red fibre one for his, less likely to mark the PCB).
-PCB.
-Teflon pillar.
-Heatsink (with heatsink compound on upper surface).
-Regulator.
-Compression washer.
-Nut.

Viewed from the side (image #2) you can see the way the uncut long legs of the regulator are turned sharply downwards towards the holes in the PCB, but still with enough curvature to take them around the edge of the metal heatsink without touching.

Image #3 is what my complete issue VI looks like at the moment - the keys were legended by printing Philoupat's scan of the keypad overlay for his Czech replica issue V here:-

https://www.vintage-radio.net/forum/...&postcount=519

...and then cutting the legends out as 10mm squares before securing them under the snap on clear covers. I chose this image to take the key legends from because they are identical to the original ones. Tim went for white on black on the keys for his issue VI which is black, like mine. I went for black characters on white partly because that's how it was originally, and partly because I'm an old duffer now and I have trouble reading the thin white characters on the black keys on my PCs in anything but good light.
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Old 24th Nov 2022, 8:41 pm   #26
Slothie
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Default Re: Idiot building a MK14 thread

Sirius's idea is good - the heatsink outlined in the construction manual (and I have on my MK14) should be considered the bare minimum. It gets quite hot, enough to be at least uncomfortable to touch, but I measured the temperature after 10 mins or so with a thermocouple on the tab of the 7805 and it was about 55 degrees in a coolish room (22 degC) with a 7.5v input or 69 degC at 9v (wouldn't recommend more than 9v). I don't think this will cause a shortened life for the regulator, but more cooling really can't harm, and you won't risk touching something hot!

Another option is to use a switching 7805 alternative like the ones advertised on eBay but I have done no testing with these as to the reliability or how much noise they output (although with all the decoupling on the Issue VI that shouldn't be an issue).

Ideally if you're going to put it in a case, mount the regulator remotely on the case or larger heatsink.
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Old 24th Nov 2022, 8:50 pm   #27
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Default Re: Idiot building a MK14 thread

I intend to work on some dual-colour keycaps when I'm building, but inspired by a comment from Mark1960, I was wondering whether there was anything like an official or common case that was used with the MK14?

I've had a quick Google and can't find too much - does anyone have one or had one so I can look at designing and 3D printing one?

Colin.
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Old 24th Nov 2022, 8:52 pm   #28
SiriusHardware
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Default Re: Idiot building a MK14 thread

Quote:
(wouldn't recommend more than 9v)
I run mine on an external 7.5V linear regulated supply to keep the voltage drop across the onboard regulator as low as possible. Still gets quite warm, especially when the original SOC VDU and its RAM expansion are also being powered through the onboard regulator.

However the Bipolar PROMs run far hotter than the heatsink does..

Edit: No Colin, there never was an official case for the MK14, people extended the display, keypad and reset switch off the PCB and built them into all sorts of enclosures. For a time mine lived in a smart executive briefcase with the PCB etc in the lower half and an opaque white perspex sheet over the top with a calculator body mounted on it. The calculator keys were wired up to the appropriate connections on the keypad edge connector and the display was positioned to 'shine' through the red window on the calculator body. That's the smartest my original MK14 ever looked, actually, it's a shame I don't have a photo of it like that.

If you do go to make an actual custom enclosure then it will need a lot of ventilation around not only the regulator but the PROMs, which run bl**dy hot, and also it will need cutouts to allow edge connectors to be plugged into the rear and side edge connectors.

Try to imagine what Rick Dickinson (designer of the ZX81 and Spectrum and Spectrum Next) would have made it look like if he had been given the job. Let's see some concept art sketches...

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Old 24th Nov 2022, 9:03 pm   #29
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Default Re: Idiot building a MK14 thread

Quote:
Originally Posted by ScottishColin View Post
I intend to work on some dual-colour keycaps when I'm building, but inspired by a comment from Mark1960, I was wondering whether there was anything like an official or common case that was used with the MK14?

I've had a quick Google and can't find too much - does anyone have one or had one so I can look at designing and 3D printing one?

Colin.
I didn'r find any case that was suitable, but I did design a "tray" for the MK14 to sit in that lines up with all the holes. stiffens the circuit board, aligns the edge connectors and prevents shorts on the bottom of the case. Its in 2 parts, the tray and a clip that secures the back of the board.

It secures with 4 screws through the keyboard holes (and bezel if you have one) and the clip at the back.

You'll need a 3d printer that has at least a 300x300 buid area because the M14 is large....
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Old 24th Nov 2022, 9:48 pm   #30
ScottishColin
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Default Re: Idiot building a MK14 thread

Thanks very much. I have a Prusa Mk3s - I'm going to have to split that one....

Colin.


Quote:
Originally Posted by Slothie View Post
Quote:
Originally Posted by ScottishColin View Post
I intend to work on some dual-colour keycaps when I'm building, but inspired by a comment from Mark1960, I was wondering whether there was anything like an official or common case that was used with the MK14?

I've had a quick Google and can't find too much - does anyone have one or had one so I can look at designing and 3D printing one?

Colin.
I didn'r find any case that was suitable, but I did design a "tray" for the MK14 to sit in that lines up with all the holes. stiffens the circuit board, aligns the edge connectors and prevents shorts on the bottom of the case. Its in 2 parts, the tray and a clip that secures the back of the board.

It secures with 4 screws through the keyboard holes (and bezel if you have one) and the clip at the back.

You'll need a 3d printer that has at least a 300x300 buid area because the M14 is large....
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Old 24th Nov 2022, 10:07 pm   #31
Slothie
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Default Re: Idiot building a MK14 thread

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Originally Posted by ScottishColin View Post
Thanks very much. I have a Prusa Mk3s - I'm going to have to split that one....

Colin.
You might be able to fit it onto the build plate diagonally. Failing that spit it in 2 and glue a bracing piece inside.
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Old 24th Nov 2022, 10:12 pm   #32
ScottishColin
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Default Re: Idiot building a MK14 thread

I can rotate it so it has one end resting on the plate and diagonally upwards (if that makes sense). It's a horrendous amount of supports though.

Bracing plate I think.

Colin.

Quote:
Originally Posted by Slothie View Post
Quote:
Originally Posted by ScottishColin View Post
Thanks very much. I have a Prusa Mk3s - I'm going to have to split that one....

Colin.
You might be able to fit it onto the build plate diagonally. Failing that spit it in 2 and glue a bracing piece inside.
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Old 24th Nov 2022, 11:11 pm   #33
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Default Re: Idiot building a MK14 thread

Quote:
Originally Posted by SiriusHardware View Post
>>
>>
Try to imagine what Rick Dickinson (designer of the ZX81 and Spectrum and Spectrum Next) would have made it look like if he had been given the job. Let's see some concept art sketches...
Rick Dickinson also worked on the design of the Spectrum Next, and he gave a talk on how he approached that at a Sinclair/Spectrum Cambridge CfCH museum special exhibition weekend a few years ago. They may have filmed this and put it on Youtube (They did for some Acorn special weekend). Sadly, Rick Dickinson passed away not long after doing that talk.

But maybe, more in keeping with that era of early home / hobbyist computers, where it was usual to go for simplicity / keep costs to a minimum, would be a vacuum-formed style case like Jupiter ace (and ZX80?) - Rather than later mass-produced but high initial tooling cost injection-moulded ABS. It maybe possible to produce something a bit like vacuum-formed ones with a wooden etc mould and stretching a heated thin plastic sheet over it - We did this once, at School,back in the early 80's IIRC.

I seem to recall there were over-heating issues with the ZX80, probably due to heatsink being too small (I know there was a lot more room in the ZX81 than the small plate it came with).
Chris Oddy found a taller one (RS 402-951) which he used on his MK14 Replica - See photos of it, here: http://www.theoddys.com/acorn/Replic...lica_mk14.html

It was rather tight against the 8154 PIO IC, due to replicating original layout, so I ended-up bending it away slightly. And I put a silicone rubber TO-220 washer under it on mine, as didn't want to rely on solder resist to insulate rather close tracks from it.
Probably don't want to have to add a small (often noisy as tend to run at higher-speed) fan inside!
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Old 24th Nov 2022, 11:38 pm   #34
SiriusHardware
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Default Re: Idiot building a MK14 thread

My personal feeling about it is that the MK14, along with many similar 'systems' at the time, was only ever meant to be used as a slap-down bare board. It didn't even have mounting holes in the right places to allow the PCB to be mounted on a chassis or inside an enclosure - the four holes at the corners of the keypad were purely for the attachment of the keypad frame.

The edge connector for the keypad was an acknowledgement of what must have been clear early on, the keypad supplied with the kit was terrible, so they made this provision for an off board keypad. No such provision was made for the display, or the reset switch for that matter, to be extended off board. Nevertheless, a lot of people including myself did put them in enclosures but they were normally rather roomy and well ventilated, like the one featured in this quirky blog entry:-

https://robdobson.com/2016/10/mk14-meets-7bot/

My own MK14 was installed in at least three different enclosures at different times but when I revived my interest in it (around 2010 or so) the first thing I did was to restore it as nearly as possible to its original bare board configuration - given that I no longer had the original keypad components.

One idea I did like was that adopted by the Z80 based 'Microprofessor' which again used bare boards, but they were slotted into a flexible plastic cover formed like a book:-

http://www.heimcomputer.de/english/c...professor.html

The empty left hand tray could be populated with optional add-on boards like the general purpose I/O board, with the connecting cable between them running through the 'mouseholes' on the two facing edges. When not in use the case could be closed up just like a book and placed in a bookshelf - pretty neat.
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Old 25th Nov 2022, 12:47 am   #35
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Default Re: Idiot building a MK14 thread

Yes, I remember using the Microprofessor at College in the late 80's / these being in the Maplin catalogue.
And someone at the RCF had for sale an updated enhanced Z80 / display version of it, they'd designed for use in education etc. (Although I can't recall if it was similarly-cased).
I do have one of these, in a slightly-larger than A4 'Book-style' case, with vacuum-formed inner plastic that retains the main board by just using 4 ridge-lips and a ledge for the board to sit on. and space under it for a 6B battery pack. See:
https://www.kandh.com.tw/dt-01-digit...ner-dt-01.html
https://www.kandh.com.tw/uploadfiles...t-01_10907.pdf


I do recall at a previous CfCH event , that someone had produced Replica Apple-1 designs and built one in a briefcase.
And along similar-lines, Tandy did their nnn-in-one experimeter's project kits in Wooden framed boxes,that some others also had clear etc lids on. Plus I built a somewhat similar idea Everyday Electronics "Tutor-Deck", used for their Teach-in series in the early 80's: https://worldradiohistory.com/UK/Eve...cs-1979-10.pdf
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Old 25th Nov 2022, 8:14 am   #36
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Default Re: Idiot building a MK14 thread

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.
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Old 25th Nov 2022, 9:32 pm   #37
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Default Re: Idiot building a MK14 thread

Just wondering: Is Colin going to do a time-lapse video of the board being built?

It's been done before, actually:

https://www.youtube.com/watch?v=vhSAMRwGL-A

This was a one-off MK14 repro PCB project that the presenter did just for himself, or so I believe. I think it pre-dates the Czech replicas by some time.
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Old 25th Nov 2022, 10:22 pm   #38
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Default Re: Idiot building a MK14 thread

That seems like a slow way to fit the sockets. Fit all the sockets in place making sure the orientation is correct. Put a piece of card over the top to hold them all in place. Flip the board over and solder opposite corners of each socket, while gently pushing down on the pcb close to each socket so they are tight to the board. With all the sockets tacked in place lift it up and check alignment and that each socket is a close fit to the board. Adjust if needed by holding the board on its edge while retouching the corner joints and pushing the sockets flat to the pcb. Lay the board components side down and solder all the rest of the socket pins.

You can fit the resistors before the sockets but best to leave capacitors and other taller components until after the sockets are fitted.
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Old 26th Nov 2022, 12:45 am   #39
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Default Re: Idiot building a MK14 thread

The thing is, for Tim that would be an actual-speed video. (Never understood how he builds things so fast...)
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Old 26th Nov 2022, 11:23 am   #40
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Default Re: Idiot building a MK14 thread

Its a shame we didn't get the scans of the PCB..... Looks like he made a good job of it though.
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