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-   -   I found it! A very sorry looking MK14. (https://www.vintage-radio.net/forum/showthread.php?t=170727)

ortek_service 21st Mar 2021 1:25 pm

Re: I found it! A very sorry looking MK14.
 
Quote:

Originally Posted by Buzby123 (Post 1355673)
Quote:

... But I've not seen much about the cassette interface. It's simply enough to knock-up on a bit of veroboard, but would be nice to have somethng a bit closer to the original, so any details on these would be useful).
You only have to ask .....

Thanks - I hadn't ever seen these around the 'net before.
So Chris O may want to add them to his MK14 webpage (crediting sources appropriately), which he's tried to put as much info he'd found in one place.

And they don't seem to be covered on the CfCH MK14 webpages, eg: http://www.computinghistory.org.uk/d...otype-of-MK14/
- but I do note that these state 50,000 MK14's were sold.

I do notice that they seemed to have used cheaper SRBP material for this PCB, whereas they used Fibreglass for the (also single-sided with top silk screen) PROM-Programmer board (that was a bit larger, but not that much, so wouldn't have thought strength was too important / cost difference that much)

SiriusHardware 21st Mar 2021 2:29 pm

Re: I found it! A very sorry looking MK14.
 
We're hijacking Buzby's thread a bit, maybe continue this (interesting) discussion re: Circuit diagram / PCB variants in the 'MK14 schematic revisions' thread?

ChrisOddy 22nd Mar 2021 9:29 am

Re: I found it! A very sorry looking MK14.
 
Quote:

Originally Posted by ortek_service (Post 1355674)
Chris Oddy only refers to the 2 he has as early and later, here:
http://theoddys.com/acorn/Acorn%20Sy...Mk14/mk14.html
- Although it seems the links are currently broken, so I will let him know.

Links now fixed, the problem occurs because I develop the website on a windows platform which doesn't care about upper and lower case filenames but the hosting Linux platforms do !

I've also corrected all references to Mk14 to MK14, I seem to remember somebody once explained what the MK refered to ?

Chris

SiriusHardware 22nd Mar 2021 9:44 am

Re: I found it! A very sorry looking MK14.
 
MicroComputer Kit, rather than 'Mark' as many read it. It's been suggested that 14 is the minimum number of ICs the machine needed to run, minus the extra RAM or RAM I/O devices.

Back to Buzby's 'Micky' system now...

Buzby123 22nd Mar 2021 10:58 am

Re: I found it! A very sorry looking MK14.
 
1 Attachment(s)
Micky with crappy sockets removed.

I've fitted a nice Cambion 40 pin for the 8060, and I've got some similar 14 pin ones. Just need to find some contemporary 16 & 18 pins to complete.

I've patched most of the top track cuts, now to move onto the bottom tracks.

Looking through my boxes of stuff, I found what I think is the original bubble display. It's a bit grubby, and it seems to have bits of 40 year old Plasticene stuck to it. ( Don't ask why, I've no idea. ) I don't need this display, but it's nice to have it.

Cheers,

Buzby

SiriusHardware 22nd Mar 2021 2:27 pm

Re: I found it! A very sorry looking MK14.
 
If the 'current' display is unpluggable then maybe make the original display 'pluggable' in the same way by adding a pin row connector or whatever matches? My own issue II PCB has an 18-way male pin row connector, the original display has a right-angle 18 way male pin row connector and the two are joined together by two SIL female sockets (like the ones used on Arduinos) soldered pin to pin at an angle of about 45 degrees and heatshrinked.

It means I can use the original display, but can easily unplug it to test or use other displays. You might actually find it more convenient to be able to plug the small display in while you are nursing the system back to health.

Buzby123 22nd Mar 2021 3:00 pm

Re: I found it! A very sorry looking MK14.
 
The display on Vicky is pluggable, I wasn't soldering my expensive bubble in permanently !.

The display on Micky is also pluggable, as that was how I fitted the off-board display back in the day.

The plugs & sockets are not compatible between Vicky & Micky, but half of a modern 40 pin IC socket makes a neat adapter !.

I've got all the tracks repaired, I think.

One issue I have is IC16 pin 1. It looks like this is one of the unused gates, as pin 2 is connected to R5, but pin 1 is loose. ( Remember, I'm restoring Micky to SoC original state, with multiple SCIOS images, so those unused gates should be connected to R5. ) I can't see any evidence of a track-cut relating to pin 1, so was it ever connected ?.

I just need some period style IC sockets to finish off. I've got 14 & 16 pin on order, but can't find any supplier for 18 pin. Any suggestions ?.

Cheers,

Buzby

SiriusHardware 22nd Mar 2021 3:19 pm

Re: I found it! A very sorry looking MK14.
 
Quote:

Originally Posted by Buzby123 (Post 1356038)
One issue I have is IC16 pin 1. It looks like this is one of the unused gates, as pin 2 is connected to R5, but pin 1 is loose.

Do you mean on the top side or the underside? Tim's image of the underside of an Issue II posted a while back in this thread should be good enough to see if anything goes to pin 1 on the underside.

If you haven't worked it out by this evening I will dig mine out and make a few measurements to see if anything goes to IC16 pin 1 on mine.

Buzby123 22nd Mar 2021 3:22 pm

Re: I found it! A very sorry looking MK14.
 
Both sides, it ain't got no connection to nuffin !

Mark1960 22nd Mar 2021 4:12 pm

Re: I found it! A very sorry looking MK14.
 
Quote:

Originally Posted by Buzby123 (Post 1356038)
I just need some period style IC sockets to finish off. I've got 14 & 16 pin on order, but can't find any supplier for 18 pin. Any suggestions ?.

You could try ebay.com or ebay.ca. I see both TI and Cambion, from us, but shipping might make it too expensive.

SiriusHardware 22nd Mar 2021 4:35 pm

Re: I found it! A very sorry looking MK14.
 
(Just remembered Mark has an original issue II as well).

Mark1960 22nd Mar 2021 4:49 pm

Re: I found it! A very sorry looking MK14.
 
No, mine is a IV.

SiriusHardware 22nd Mar 2021 5:15 pm

Re: I found it! A very sorry looking MK14.
 
Sorry, I don't know where I got that from.

Anyway...

I confirm...

No connection to IC16 pin 1 on the underside
No connection to IC16 pin 1 on the top side.

I wasn't able to see much underneath the IC16 socket so I took the IC out of the socket and measured from the pin 1 socket to +5V, 0V and various random points, all read infinite resistance on highest Megohms range in both directions. I think there really is no connection.

On Buzby's photo in #205 it looks to me as though the VIAs above left and above right of IC16 which originally connected...

-Pin 1 of IC18 to pin 10 (CE2) of IC6 and IC7 (RAM)
and
-Pin 2 of IC18 to pin 10 (CE2) of IC4 and IC5 (RAM)

Have been drilled out, so I assume they have now been, or will be, reinstated with through-hole links. The one above-left of IC16 needs to be bridged across the top side break as well as restored going through the hole.

I'll keep the issue II handy for a while in case you need any other connections checked.

SiriusHardware 22nd Mar 2021 5:30 pm

Re: I found it! A very sorry looking MK14.
 
I've always held the belief that SOC didn't bother with anything unnecessary, like supply decoupling capacitors, but actually in my short voyage around the PCB I I've just realised that there are two - one of them (C4) is right in the middle of Buzby's photo, the other (C3) is near the bottom ends of IC5 and IC7.

Who knew?

Buzby123 22nd Mar 2021 6:04 pm

Re: I found it! A very sorry looking MK14.
 
The circuit diagram shows 3 decoupling caps, C3,C4,C5, on the output from the 7805, bottom left of dwg.

The board layout diagram only shows C3 & C4, and those are the only ones on Micky.

How did these boards work so well with only two decoupling caps ?

Regarding drilled-out vias, I'm certain I never drilled any holes, but I'm still checking. It's much easier to do this before I fit the sockets.

Cheers,

Buzby

ortek_service 22nd Mar 2021 6:08 pm

Re: I found it! A very sorry looking MK14.
 
The decoupling arrangements on the MK14 were rather bizarre.
- Very little / not on IC's and a rather large electrolytic that seems unnecessary unless the board was powered from an un-smoothed rectified-only AC-adaptor.

I recall a Computer lecturer once telling us that he'd found early computers sometimes with no decoupling only worked as not everything clocked synchronously at the same time so reducing peak current demands.

I wonder if they'd adopted the rumoured TV design cost-cutting approach, of removing capacitors until it stopped working than putting last one back in - Not good to have such a marginal design, for reliability.

SiriusHardware 22nd Mar 2021 6:13 pm

Re: I found it! A very sorry looking MK14.
 
Maybe it's just your photo but it looks like you have taken out two pads on the top side just above-left and above-right of IC16. You haven't drilled them right through but you have used a drill bit to remove those top side pads, or it looks very much that way to me.

If you did, you would have done that to disconnect the outputs of the address decoder from the CE2 inputs of the onboard RAMs so you could direct those chip enables to something else, possibly your battery backed RAMs, which you may have had mapped into the address space normally occupied by the onboard 2111s?

Buzby123 22nd Mar 2021 6:21 pm

Re: I found it! A very sorry looking MK14.
 
It's just a trick of the light, those vias have not been touched. The 'hole' is just a dent in the solder, probably exacerbated by my prodding it with a multimeter probe.

Have you noticed the two sets of extra holes at the bottom of IC12 & 13 ?

It looks like they used an 18 pin template for a 16 pin chip.

SiriusHardware 22nd Mar 2021 6:32 pm

Re: I found it! A very sorry looking MK14.
 
1 Attachment(s)
Yes, I did spot that too. Makes me wonder how we ever managed to get these things working (and yet we did).

This is what my vias (above IC16) look like. On your photo I couldn't even see the holes through the centre, so I convinced myself you must have taken the pads off.

What's the next job?

Slothie 22nd Mar 2021 7:09 pm

Re: I found it! A very sorry looking MK14.
 
On my original MK14 prototype I only added the decoupling capacitors on the SoC schematic, and it worked well enough, although when I looked at the waveforms on the power rails or any signal they were noisy as anything, so much that I wondered at it working at all, which is why when I produced the second version (1.2) I added as may decoupling caps as possible, as others had requested. I reasoned I could always leave them out, but they are so cheap I just populated all of them.
The big electrolytic seems mostly decorative these days, but I guess that depends on the power supply you plug in. Most of the "wall wart" power supplies I owned in the 70s/80s had hardly any smoothing as you could always hear hum when I powered my radio or cassette player from them, so I imagine SoC put them in to stabilise a less-than-stellar "battery eliminator" as we used to call them.

Buzby123 22nd Mar 2021 7:22 pm

Re: I found it! A very sorry looking MK14.
 
1 Attachment(s)
All my vias are filled with solder. Not sure if I did that, or it's how it was delivered.

I've been wondering why I had such a mix of IC sockets. Surely the kit must have supplied all the correct parts, not those horrible pin-strips like I had for the 8060 ?.

I'm continuing to check diagram against board, and re-checking all around IC16,17,18 which is where I did most of the track cuts. ( Remember, I had removed IC16 completely ! )

I won't be able to power up until I find some 'period style' 18 pin sockets, so tomorrow I'm going to try to resuscitate Micky's original bubble display. It will be a cool sight to see, Micky & Vicky side-by-side, both with their tiny LEDs shining !

SiriusHardware 22nd Mar 2021 7:25 pm

Re: I found it! A very sorry looking MK14.
 
There was actually an official branded / badged MK14 power supply, someone here, possibly Gertk64 (who has not been around for a while) had one. As we all built the machines ourselves we were a resourceful lot and generally already had something suitable, so I doubt whether many of the official ones were sold.

The 'real thing' was just the usual mains transformer / bridge / smoothing capacitor, nothing special, but I bet if one came up for sale it would go well up into the tens of pounds as long as it had its Science of Cambridge label present and intact.

SiriusHardware 22nd Mar 2021 7:27 pm

Re: I found it! A very sorry looking MK14.
 
Quote:

the kit must have supplied all the correct parts
Nope, the kit did not include sockets, at least not during the issue II period. To this day, all of the 18 pin ICs on my issue II are soldered in place because just like you now, I had problems finding 18 pin sockets and I was impatient to get the thing up and running.

ortek_service 22nd Mar 2021 7:52 pm

Re: I found it! A very sorry looking MK14.
 
Quote:

Originally Posted by SiriusHardware (Post 1356172)
There was actually an official branded / badged MK14 power supply, someone here, possibly Gertk64 (who has not been around for a while) had one. As we all built the machines ourselves we were a resourceful lot and generally already had something suitable, so I doubt whether many of the official ones were sold.

The 'real thing' was just the usual mains transformer / bridge / smoothing capacitor, nothing special, but I bet if one came up for sale it would go well up into the tens of pounds as long as it had its Science of Cambridge label present and intact.

They do give a 8V 600mA spec for it, in the add shown here: http://theoddys.com/acorn/Acorn%20Sy...4%20Advert.jpg
But unfortunately there's not a good view of a label, to make a replica.

The original PSU's for equipment often seem to get lost / thrown out - especially ones with moulded DC plugs when the wire gets bent too much and breaks, although this one must have had to be hard-wired. So can add to the rarity. Back then, I did gut a Commodore LED calculator one that always buzzed-loudly to reuse the case I've still got - which does look quite similar to the MK14 one.

Timbucus 22nd Mar 2021 8:38 pm

Re: I found it! A very sorry looking MK14.
 
1 Attachment(s)
If you want to make a replica PSU you could probably adapt this photo which is what I plan to do when I find a suitable looking one.

Again snatched from an ebay sale in the days before I kept good records of sources so apologies to anyone who now owns it...

Timbucus 22nd Mar 2021 8:40 pm

Re: I found it! A very sorry looking MK14.
 
1 Attachment(s)
Not sure if this one helps as well but, it is an Issue IV naked on top...

Buzby123 22nd Mar 2021 9:06 pm

Re: I found it! A very sorry looking MK14.
 
Quote:

Originally Posted by SiriusHardware (Post 1356174)
Nope, the kit did not include sockets, at least not during the issue II period.

I can't remember the kit, or actually building the board. ( I've had a lot of sleeps since then ! ) Did it come in a box, or was it just a jiffy bag of bits ?.

SiriusHardware 22nd Mar 2021 9:09 pm

Re: I found it! A very sorry looking MK14.
 
I'm sorry to have to tell you that Tim can answer this question better than I can. Take it away, Tim...

Timbucus 22nd Mar 2021 9:14 pm

Re: I found it! A very sorry looking MK14.
 
Quote:

Originally Posted by SiriusHardware (Post 1356221)
I'm sorry to have to tell you that Tim can answer this question better than I can. Take it away, Tim...

Really - I expect you want photographs of it as well don't you...

http://oldcomp.cz/viewtopic.php?f=89...eb9a7&start=45

SiriusHardware 22nd Mar 2021 9:35 pm

Re: I found it! A very sorry looking MK14.
 
There you go.

Scroll down to the ~13th post on that forum page, and there you see an original unbuilt, boxed kit side by side with a modern replica of the kit. You can click on the image for improved bigness. Note the utter lack of sockets.

Timbucus 22nd Mar 2021 9:54 pm

Re: I found it! A very sorry looking MK14.
 
Also slightly higher up is the outer sleeve as well

ortek_service 22nd Mar 2021 11:47 pm

Re: I found it! A very sorry looking MK14.
 
Also see here for a clearer one of what was supplied inside the box:

http://theoddys.com/acorn/Acorn%20Sy...MK14%20Kit.jpg

(I do recall seeing it on another website, that Chris got itoff - I think he may have got them to send him a higher res. one, and he may have credited this elsewhere)

Buzby123 23rd Mar 2021 12:08 am

Re: I found it! A very sorry looking MK14.
 
Quote:

Originally Posted by ortek_service (Post 1356266)
Also see here for a clearer one of what was supplied inside the box ...

That's not an issue 2 like mine. This one's got clicky buttons, not that rubber sheet I had to put up with.

I still can't picture what I received 40 odd years ago, but then I did have lots of other interests at the time. Remembering packaging was not as important as remembering girls phone numbers !.

SiriusHardware 23rd Mar 2021 8:57 am

Re: I found it! A very sorry looking MK14.
 
For the record, my issue II arrived in a very similar folded cardboard package. I still had that bit of antistatic foam that the ICs came in for years and years afterwards, maybe even still do.

Buzby123 23rd Mar 2021 10:11 am

Re: I found it! A very sorry looking MK14.
 
2 Attachment(s)
Todays project - Resuscitating an original MK14 display.

I found this while looking for something else.

Fairly sure this is Micky's original display. No idea why it's covered in Plasticine, maybe it was some temporary holding method, from the days before BluTac was invented.

I'm going to clean off the crap, clean the solder holes, fit a plug, and try it in Vicky.

Buzby123 23rd Mar 2021 11:16 am

Re: I found it! A very sorry looking MK14.
 
1 Attachment(s)
It works !.

A couple of lifted tracks, they'd gone green under the gunk, so a bit of soldering both sides of the PCB fixed that.

Now I will be able to show Micky & Vicky running side-by-side !.

SiriusHardware 23rd Mar 2021 11:20 am

Re: I found it! A very sorry looking MK14.
 
Still nice and bright after all this time! Probably doesn't have too many miles on the clock, that display.

ortek_service 23rd Mar 2021 11:25 am

Re: I found it! A very sorry looking MK14.
 
Quote:

Originally Posted by Buzby123 (Post 1356269)
Quote:

Originally Posted by ortek_service (Post 1356266)
Also see here for a clearer one of what was supplied inside the box ...

That's not an issue 2 like mine. This one's got clicky buttons, not that rubber sheet I had to put up with.

Well it does hopefully show that IC sockets weren't included - in that version at least. I would have expected sockets to have been in there in the early version at least, being as SoC adverts all show all of the IC's socketed (So a bit misleading if they never included these, and you had to buy your own), and maybe then removed these for cost-cutting.
I suppose they could have added them later on, as even ready-built ZX81's & Spectrum's often had many of the more expensive IC's socketed, but was a bit variable over the years as to which ones had sockets (Luckily, always the ULA at least).

SiriusHardware 23rd Mar 2021 3:39 pm

Re: I found it! A very sorry looking MK14.
 
I'm certain sockets were never supplied with MK14 kits as the instructions state that it's advisable to fit sockets, which would be a strange thing to say if sockets were actually included. If they gave you them, then of course you would fit them.

They also advised the use of a heatsink on the regulator, and they didn't supply one of those either...

TonyDuell 23rd Mar 2021 3:59 pm

Re: I found it! A very sorry looking MK14.
 
I seem to remember that either SoC or one of the hobbyist suppliers (probably the former) sold a pack of the right sockets for the MK14 board. I know I got it when I built my MK14. The large electrolytic capacitor was 'optional', it was not included in the kit and I never fitted it as the machine worked on my homebrew power supply without it.

I also remember a note about the using the correct 16 holes in those 18 pin locations. Maybe a slip of paper tucked in the manual. I doubt I could find it now though.

Buzby123 26th Mar 2021 2:33 pm

Re: I found it! A very sorry looking MK14.
 
1 Attachment(s)
Micky has awoken ...

SiriusHardware 26th Mar 2021 2:39 pm

Re: I found it! A very sorry looking MK14.
 
That didn't take long! Now you have to decide how far to go with the restoration to its 'historic' form factor...

Buzby123 26th Mar 2021 3:04 pm

Re: I found it! A very sorry looking MK14.
 
1 Attachment(s)
I'm not restoring the daughterboard system, it's too messy and precarious. Too many chances to damage the expensive bits. If I was to build a 'new' daughterboard I'd take a completlely different tack about it.

Micky will be going back in his cabinet, the lamps and switches on there should still work, as they are all driven from the 8154 edge connector. The cassette interface will be reinstalled, then I'll have to find a way to test that. The keyboard and display should work, those are the first things I'll be testing.

It's been a long and arduous journey to get Micky alive again.

I could not, and maybe would not, have done it without the help and support from this forum.

Thanks to you all.

Buzby

SiriusHardware 26th Mar 2021 5:36 pm

Re: I found it! A very sorry looking MK14.
 
They make a nice couple. ;) I'm guessing you have a 4.00MHz crystal in Vicky, if so Micky will be significantly faster than his younger sister.

It would be good if you could post a nice YT video of it working when it's all up and running and back in the original enclosure.

SiriusHardware 26th Mar 2021 5:55 pm

Re: I found it! A very sorry looking MK14.
 
As far as testing the cassette interface is concerned any Laptop or PC of a certain age will have proper audio inputs and outputs which you can use in conjunction with something as simple as Windows 'Sound Recorder' or something a bit more full featured (but free) like 'Audacity' to record the audio output from the MK14 Cassette Interface and play it back into it.

Once you have an MK14 program saved as an audio file you can play it back into the MK14 using almost anything, I successfully used both an old Win XP netbook and a little Creative Technology MP3 player to play MK14 tape files back into the machine when I was testing the hex-to-audio conversion software by twostickes (see his recent thread).

The main thing, if you are using anything which has stereo audio output to play files back in, is to use only one audio output channel, either left or right, don't join them both together to connect to the mono input of the cassette interface. I have a lead made up which has a stereo plug at the laptop / MP3 / Smartphone end and a mono plug at the MK14 interface end. In the stereo plug, only the left channel audio output is connected through to audio-in at the 'mono' MK14 end.

Buzby123 26th Mar 2021 6:24 pm

Re: I found it! A very sorry looking MK14.
 
Quote:

Originally Posted by SiriusHardware (Post 1357640)
I'm guessing you have a 4.00MHz crystal in Vicky, if so Micky will be significantly faster than his younger sister.

Nope, Vicky's xtal is labelled 4.433, so I'm expecting it to be 4.433618, same as Micky.
Quote:

It would be good if you could post a nice YT video of it working when it's all up and running and back in the original enclosure.
I certainly will !.

SiriusHardware 26th Mar 2021 6:43 pm

Re: I found it! A very sorry looking MK14.
 
I did actually buy a 4.43MHz crystal to put in my issue VI as well because some of the old manual software such as 'Music Box' and 'Digital Clock' depends on the crystal being that frequency, but then the prospect of reconnecting my VDU (and Karen's 'Ortonview' alternative), both of which prefer 4.00MHz, was just too good to resist so I never have changed it.

Did you see that original MK14 in another thread which had the keypad restored by soldering ultra low profile SMD switches (we thought they were domes at first) to the keypad fingers and then placing an authentic looking keypad overlay over the top? It was so nicely done I would consider doing that to mine if it did not already have a reasonable substitute keypad fitted in place of the original one.

Buzby123 26th Mar 2021 6:58 pm

Re: I found it! A very sorry looking MK14.
 
Quote:

Originally Posted by SiriusHardware (Post 1357664)
Did you see that original MK14 in another thread which had the keypad restored by soldering ultra low profile SMD switches ....

No, I haven't seen that. I'm not going to put a new keyboard on Micky. When he's in his case there is no need for one, but I probably will sneak in one of those Arduino downloaders.

SiriusHardware 26th Mar 2021 7:14 pm

Re: I found it! A very sorry looking MK14.
 
You could maybe panel-mount a 15 way sub-D connector in a cutout on the right hand side of the enclosure and wire the external keypad connector to that. That way you don't have to have anything non-period inside the enclosure, you just plug your uploader of choice into the sub-D connector, load something up and then unplug it.

It would mean modifying the 'historic' housing slightly, but sub-D connectors are as 1970s as they are current, so it would look perfectly in keeping. It would also let you plug in a high quality external keypad or even a keyboard with more keys on it, should the mood ever take you. (The MK14's row / column matrix can support quite a few more than the 20 keys on the original keypad).

Edit: A full sized keyboard would need to use all of the row / column lines including two which the standard keypad does not use, so if that was the plan it would be better to go up to a 25-way connector (there are 19 way sub-Ds but they are rather rare now).

Buzby123 26th Mar 2021 7:46 pm

Re: I found it! A very sorry looking MK14.
 
That's a good idea.

I'm not going to be able to do much over the weekend, so it will be next week before Micky gets back in his case. ( Actually, I'm putting Vicky in first, just to do a test without risking Micky. )


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