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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.


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