UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Computers

Notices

Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

Closed Thread
 
Thread Tools
Old 8th Nov 2022, 8:56 pm   #1
IanB_63
Triode
 
IanB_63's Avatar
 
Join Date: Nov 2022
Location: Newport, Monmouthshire, Wales, UK.
Posts: 16
Default Unbuilt original MK14 VDU

Nice to see so much MK14 activity in this forum.

I have an original MK14 which I built back in the late 70s and an original unbuilt MK14 VDU kit which I bought from Enrico Tedeshi back in February 2001.
He wrote the Sinclair Archeology book and had a large collection of Sinclair artefacts including many prototypes, a lot of which appeared for sale online in 2015 shortly after he died.

I very nearly got an MK14 VDU back in 1980 but the ZX80 was launched just at that time so I ended up getting that instead.
Back in 2001 there was very little info available on the MK14 VDU and when I saw one advertised on Enrico's website I decided to buy it to see what I missed out on but at the time I didn't realise it was an unbuilt kit as it was just described as an MK14 VDU.

As it was an unbuilt kit and thus extremely rare (Enrico only had one other one) I didn't really want to actually build it so it's nice to see there are now reproductions being made so maybe I will finally get to see firsthand what the MK14 VDU was like.

So are any PCBs for reproduction VDUs available at the moment?
Attached Thumbnails
Click image for larger version

Name:	MK14_kit.jpg
Views:	181
Size:	92.2 KB
ID:	267705  
IanB_63 is offline  
Old 8th Nov 2022, 9:34 pm   #2
Mark1960
Octode
 
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 1,265
Default Re: Unbuilt original MK14 VDU

Welcome to the forum. Note your first few posts may be delayed until reviewed by an admin, to help keep the site free from spam.

Timbucus has a replica of the SoC vdu, I think from a guy called Martin in Czech republic. I don’t know if they are still available.

It would be nice to get a high quality scan of both sides of an original unpopulated vdu pcb if you are prepared to do that with yours.

There are a few emulations of the MK14 vdu that have been designed recently. Slothie designed a pcb for Karen Orton’s PIC based design. Realtime has recently designed one using a cpld and a cpld replacement of the character generator. Coolsnaz2 has a raspberry pi based MK14 vdu.

Last edited by Mark1960; 8th Nov 2022 at 9:35 pm. Reason: Correct typo
Mark1960 is online now  
Old 8th Nov 2022, 9:55 pm   #3
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,485
Default Re: Unbuilt original MK14 VDU

Hi, Welcome to the forum. There is a wealth of information about the MK14 spread over many threads here, if only you can ever find the time to read them all.

The only true replica of the SOC VDU (an original example of which you have there) was made by Martin Lukasec (spelling?) who also made the most visually accurate replica of the issue V MK14 PCB to date, even going to the extent of having some new keypad membranes made. His page about the replica VDU is here:-

https://www.8bity.cz/2018/mk14-vdu-v...-unit-replica/

I don't think he is currently making any more but I could be wrong, so try asking him via that page / that site. You are in the unique position of already having all of the parts, so try asking him if he can sell you a PCB only. If he has stopped selling the kits it may be because one or more of the parts are too hard to find now. Not a problem for you.

If not, I have some suggestions for you:

(1) If you are handy with any of the PCB design packages like Kicad, design and produce your own exact replica of the PCB. You are in the rare position of having a genuine PCB from which you can take measurements and scans. Put sockets in your replica PCB and fit the chips from the kit into it - any other components like passive components, buy duplicates and fit those into your replica PCB leaving the original solder-fit components unused and untouched. That will allow you to play with your VDU without building up the original PCB.

(2) Similar to above, but if you aren't familiar with PCB design packages - build a replica on stripboard, fit sockets, fit the chips from the kit and play with the VDU that way leaving the original PCB and original passive components untouched.

(3) Build an 'Ortonview', this is a hardware emulator of the SOC VDU based on a 40-pin PIC chip and not much else, designed by Karen Orton just before she passed away. Information about that in the later stages of this thread:

https://www.vintage-radio.net/forum/...d.php?t=162766

and continuing in this thread:

https://vintage-radio.net/forum/showthread.php?t=181460

(4) Buy a 'Realview', only just recently designed by forum member 'Realtime' here on this forum, the thread for that is here:-

https://vintage-radio.net/forum/showthread.php?t=194034

(5) Forum member Coolsnaz2 has combined a dual-port RAM with a Raspberry Pi to make yet another VDU emulator, using the Pi to render the VDU display on an HDMI screen.

https://vintage-radio.net/forum/showthread.php?t=193351
SiriusHardware is offline  
Old 9th Nov 2022, 12:12 am   #4
IanB_63
Triode
 
IanB_63's Avatar
 
Join Date: Nov 2022
Location: Newport, Monmouthshire, Wales, UK.
Posts: 16
Default Re: Unbuilt original MK14 VDU

Quote:
Originally Posted by SiriusHardware View Post
There is a wealth of information about the MK14 spread over many threads here, if only you can ever find the time to read them all.
Thanks for the comprehensive summary.

Quote:
Originally Posted by SiriusHardware View Post
(1) If you are handy with any of the PCB design packages like Kicad, design and produce your own exact replica of the PCB.
Yes I am familiar with Kicad and have considered doing exactly that but a shortcut would be welcome as I have many other projects to work on.

One quick question:
One of your posts mentioned that an alternative MK14 crystal (4Mhz) was supplied with the VDU but there is no crystal in the kit and the manual only mentions cryptically that the clock should be 4Mhz. It doesn't say anything about fitting one so do you know if one was actually supplied or was that just a hint about fitting one.

Using 4Mhz would be understandable though as that would mean 256 clock cycles per line for exactly 64uS which would keep the counter logic simple.
Running at 4.433 Mhz would work but would result in a 55Hz video signal although most old B&W TVs of the time would likely cope with that as they could also cope with the 60Hz from the Atom which was even more out of tolerance.

I'll have to add a profile for the MK14 VDU to the RGBtoHDMI converter project (I'm currently the main developer on that) See:
https://github.com/hoglet67/RGBtoHDMI/wiki

BTW are you aware of this web site which is no longer available:
https://web.archive.org/web/20061218...4emu/index.htm
I actually implemented the Pico Basic detailed there on my MK14 BITD
The original article is here:
http://www.flaxcottage.com/ComputingToday/8004.pdf
IanB_63 is offline  
Old 9th Nov 2022, 11:00 am   #5
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,485
Default Re: Unbuilt original MK14 VDU

4MHz crystal was usually supplied with the VDU kit - a 'conventional' crystal (not huge, like the original one) - grey shrink wrap with black lettering. The DM8678 character generator IC was not, as it was an optional extra but it could be ordered along with the kit. I wonder if yours has one with it?

The Robson site regarding all things MK14 used to be the go-to resource but it went offline, then I think was resurrected by MK14man (who made the interesting noughties MK14 replicas using 'modern' technology). I didn't realise it had gone offline again so thanks for pointing out that it is still available via the archive site.

The RGBtoHDMI project is a fantastic project which will be the saving of many old devices as working displays with SCART and AV inputs get progressively rarer. I don't know whether it would be possible, in your proposed MK14 profile, to allow for the possibility of either frame rate (Derived from 4.00MHz / Derived from 4.43 MHz) from the MK14 VDU.
SiriusHardware is offline  
Old 9th Nov 2022, 2:33 pm   #6
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,485
Default Re: Unbuilt original MK14 VDU

Quote:
The original article is here:
Great article on PICO basic (page 57-onwards in the COMPUTING TODAY linked to in #4 - I was initially distracted by the 'Ambush' and 'SC/MP Dice' programs for MK14 (p42, p45) and there is also a TRITON cassette interface test routine which may interest Tim (p43).

I was never able to run anything as ambitious as PICO BASIC back in the day because my original MK14 never went beyond the 'official' 640 bytes of onboard memory - being issue II, it didn't have the 'hole' at 0200-07FF into which to map additional memory, nor did it have contact fingers on the lower side of the rear edge connector, to which to wire the bus signals required by expansions.

I have a feeling Tim(bucus) already knew about PICO BASIC and may possibly already have it in Hex File form, no doubt he will confirm / deny if he ever reads this.
SiriusHardware is offline  
Old 9th Nov 2022, 7:23 pm   #7
Buzby123
Heptode
 
Buzby123's Avatar
 
Join Date: Oct 2011
Location: Culcheth, Cheshire, UK.
Posts: 637
Default Re: Unbuilt original MK14 VDU

I bought the tape of PICO-BASIC way back in the day. Micky ( wasn't called that then ) had the extra RAM space needed to run.

I just found PICO to be too limited, mainly due to how the display and keyboard were not really suited for BASIC. Played with it for a few hours, then gave up.

So somewhere I've probably still got that tape, and some of the 'programming sheets' to ease the laborious programming.
Buzby123 is offline  
Old 9th Nov 2022, 8:24 pm   #8
IanB_63
Triode
 
IanB_63's Avatar
 
Join Date: Nov 2022
Location: Newport, Monmouthshire, Wales, UK.
Posts: 16
Default Re: Unbuilt original MK14 VDU

Quote:
Originally Posted by SiriusHardware View Post
4MHz crystal was usually supplied with the VDU kit - a 'conventional' crystal (not huge, like the original one) - grey shrink wrap with black lettering.
Well I suppose the crystal might have been taken and used for something else in the 20 years or so before the kit came into my possession but it's strange that the manual barely acknowledges it.

Quote:
Originally Posted by SiriusHardware View Post
The DM8678 character generator IC was not, as it was an optional extra but it could be ordered along with the kit. I wonder if yours has one with it?
Yes it does have the DM8678CAB chip

Quote:
Originally Posted by SiriusHardware View Post
thanks for pointing out that it is still available via the archive site.
The wayback machine is very useful for such sites

Quote:
Originally Posted by SiriusHardware View Post
I don't know whether it would be possible, in your proposed MK14 profile, to allow for the possibility of either frame rate (Derived from 4.00MHz / Derived from 4.43 MHz) from the MK14 VDU.
Yes it's possible using the Clock Tolerance setting and that is already used to a lesser extent with the profile for the Dragon 32 which originally had a 14.318181Mhz crystal but later boards were changed to a 14.218Mhz crystal to reduce beat patterns with the colour subcarrier.
You could also convert the 55Hz output to either 50Hz or 60Hz if your monitor didn't support 55hz at the expense of some frame dropping/repeats.
Using 4.43Mz might be the better option for compatibility with other software.

The only potential issue I can see is that it looks like the sync pulses are being shaped by resistor/capacitor networks and that can cause problems in accurately sampling the pixels as the relative phase of the pixels to sync pulse will drift with time/temperature. It should still work but the auto calibration would have to be run occasionally. Picking up the digital signals at appropriate points might work around that but it's not as simple as using the composite video output.
IanB_63 is offline  
Old 9th Nov 2022, 9:29 pm   #9
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,485
Default Re: Unbuilt original MK14 VDU

As per your reasoning in #4 it does make sense for the clock to need to be changed to 4MHz because, while some TVs of that era may have been able to lock on an out of range video signal, many others would not and would just lose hold and would not be able to adjust far enough to regain hold.

It's just a pity that SOC didn't go with a 4.00 MHz crystal in the first place but of course the reason they didn't is that 4.43MHz ones were abundant and cheap due to their widespread use in colour TVs at that time.

As you say the change to a 4.00MHz crystal does have consequences for some of the example programs from the manual such as 'digital clock' and 'music box' which were both written with software timing dependent on the original clock frequency, so if it is possible to retain the 4.43MHz crystal and use the VDU, so much the better.
SiriusHardware is offline  
Old 9th Nov 2022, 11:14 pm   #10
Timbucus
Octode
 
Join Date: Mar 2019
Location: Barry, Vale of Glamorgan, Wales, UK.
Posts: 1,362
Default Re: Unbuilt original MK14 VDU

Quote:
Originally Posted by SiriusHardware View Post
Quote:
The original article is here:
...

I have a feeling Tim(bucus) already knew about PICO BASIC and may possibly already have it in Hex File form, no doubt he will confirm / deny if he ever reads this.
Yes I have the file and have run it a few times quite a challenge! As usual Paul had got there before me and created an ASM file. It was great to catch up with him at the RetroFest actually.

PicoBASIC.zip
Timbucus is offline  
Old 10th Nov 2022, 1:46 am   #11
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,485
Default Re: Unbuilt original MK14 VDU

IanB_63's link to the Computing Today article set me off trawling through all the rest of the issues as far as the end of 1980, although the MK14 specifically is rather under represented until January 1980 when 'MPUs by Experiment' turns specifically to the MK14 and becomes quite a good supplement to the official manual from that point until the series ends in June 1980.

Parallel to that, there is a series called 'Microlink' which described various forms of simple hardware interfacing to the MK14 and Acorn system 1, the common factor being the 8154 I/O port device used in both machines.

However - another thing I noticed was a letter in the August 1980 CT (Page 11) from the creator of MK14 Pico Basic to say that it had been improved in a number of ways, for example offering support for negative numbers, and inviting readers to get in touch for details of that version.

So - which version is it that is 'in the wild', the version published in the May 1980 CT, or the enhanced version offered by its creator in the August 1980 CT?
SiriusHardware is offline  
Old 10th Nov 2022, 3:19 pm   #12
IanB_63
Triode
 
IanB_63's Avatar
 
Join Date: Nov 2022
Location: Newport, Monmouthshire, Wales, UK.
Posts: 16
Default Re: Unbuilt original MK14 VDU

Quote:
Originally Posted by SiriusHardware View Post
However - another thing I noticed was a letter in the August 1980 CT (Page 11) from the creator of MK14 Pico Basic to say that it had been improved in a number of ways, for example offering support for negative numbers, and inviting readers to get in touch for details of that version.

So - which version is it that is 'in the wild', the version published in the May 1980 CT, or the enhanced version offered by its creator in the August 1980 CT?
I think the copy 'in the wild' is likely to be the one Paul typed in from the the CT article which was included in the bundle of documentation I sent him back in 1998

However Buzby123 mentions:
Quote:
Originally Posted by Buzby123 View Post
I bought the tape of PICO-BASIC way back in the day
So as that was a purchased tape, maybe it was the later version
IanB_63 is offline  
Old 11th Nov 2022, 2:28 am   #13
IanB_63
Triode
 
IanB_63's Avatar
 
Join Date: Nov 2022
Location: Newport, Monmouthshire, Wales, UK.
Posts: 16
Default Re: Unbuilt original MK14 VDU

The Sinclair Archeology book I mentioned above is available for download here:

https://www.sinclair4ever.com/2017/0...rcheology-pdf/
IanB_63 is offline  
Old 11th Nov 2022, 10:14 am   #14
Realtime
Hexode
 
Join Date: Jan 2021
Location: Ashford, Kent, UK
Posts: 318
Default Re: Unbuilt original MK14 VDU

Thanks for posting the link. Just skimmed through it quickly - looking forward to having a proper read later.
Realtime is offline  
Old 11th Nov 2022, 3:18 pm   #15
IanB_63
Triode
 
IanB_63's Avatar
 
Join Date: Nov 2022
Location: Newport, Monmouthshire, Wales, UK.
Posts: 16
Default Re: Unbuilt original MK14 VDU

This is some of the prototypes that Enrico had that went up for auction after he died:

http://www.retrogamescollector.com/s...types-auction/

The article mentions he got them from Clive Sinclair during an office clearout so perhaps that's where the VDU kits came from as well.
IanB_63 is offline  
Old 17th Nov 2022, 1:09 am   #16
Slothie
Octode
 
Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 1,287
Default Re: Unbuilt original MK14 VDU

Quote:
Originally Posted by Mark1960 View Post
It would be nice to get a high quality scan of both sides of an original unpopulated vdu pcb if you are prepared to do that with yours.
I would second this request. I'd like to build a MK14 VDU, I started to design a layout in KICAD but the schematic is a little ambiguous, and I'd prefer to make something more authentic.

In any case, it would be good for archival purposes, as I haven't seen good quality pictures of an unpopulated board despite much digging.
Slothie is offline  
Old 17th Nov 2022, 1:22 am   #17
Mark1960
Octode
 
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 1,265
Default Re: Unbuilt original MK14 VDU

If anybody does design a pcb then please change the 74L86 to 74LS86, I’m sure a simple RC on each of the outputs could compensate for any extra delay that needs to be added.
Mark1960 is online now  
Old 17th Nov 2022, 12:51 pm   #18
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,485
Default Re: Unbuilt original MK14 VDU

While it would certainly be good to have verbatim scans of the SOC VDU PCB there are a few reasons why I think actually building one might be less of a priority than it used to be:

The original SOC VDU has a few shortcomings, most notably no onboard RAM of its own, which was always a crippling limitation until you could paste some in alongside the VDU. The image quality of the original VDU is not 100% in graphics mode due to the fact that it renders the image with a thin gap between each block of 8 pixels causing the effect we have come to know as 'jail bars'. In short, it's no longer the best VDU available for the MK14. Add to that a couple of awkward parts - not only the 74L86 but the character generator - (although that particular situation has been alleviated by the timely arrival of Realtime's char gen substitute) and I don't really know if reproducing the PCBs is worth the trouble.

Now, we have Ortonview which (thanks to Slothie's PCB) comes with onboard RAM and generates clean, sharp video output with no jail bars in graphics mode, and of course we now have RealView which incorporates not only extra memory but other refinements like correct implementation of the back porches to keep modern TVs happy, plus the 'individual inverse characters' feature which can only be achieved on the SOC VDU with a bodge.

My original SOC VDU is built up of course, as is Tim's identical replica - if anyone is serious about making a reproduction I would be happy to scan the underside which would at least show the overall size and the relative placements of the pads for all of the ICs plus the tracks on that side of the PCB. I would also be happy to meter out any top side connections which there are any queries about.

It would obviously be more straightforward if IanB_63 would be kind enough to post some high quality scans of his unbuilt PCB - if he would then I would ask that a ruler / rule be laid against the long edge of the PCB during the scans to make it easy to verify that an image of the PCB displayed on a screen or printed on paper is actual size. (We can adjust the size of the displayed image or printed image until the ruler in the image / printout is the same size as an actual ruler held up against it).

Last edited by SiriusHardware; 17th Nov 2022 at 1:18 pm.
SiriusHardware is offline  
Old 17th Nov 2022, 4:17 pm   #19
Slothie
Octode
 
Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 1,287
Default Re: Unbuilt original MK14 VDU

One of the reasons I stopped on my attempts to enter the schematic, other than the problems with some of the counter pins not being marked, was the Ortonview which promised better results, especially with the Issue VI. I am still working on producing a v2 Ortonview board, once all the remaining fixes/upgrades have been completed, as I see it as a good substitute for the MK14 VDU especially now I have got it working with the 16F887 which is in current production.

However, I still like the idea of any information, or good pictures of original boards are valuable, as information about late 70s/early 80s computers is rapidly disappearing and possibly lost forever, as Tim has demonstrated with the Scrumpi 2/3,
Slothie is offline  
Old 18th Nov 2022, 10:11 am   #20
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,485
Default Re: Unbuilt original MK14 VDU

A point of information, you (Slothie) mentioned that some of the counter pins on the diagram for the SOC VDU were not numbered, but I have just looked at my copy and actually all of the 4040 etc pins seem to be labelled.

There is a copy of the same version of the document attached to this post (Diagram is on the last page).

https://www.vintage-radio.net/forum/...63&postcount=3

Am I missing something?
SiriusHardware is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 4:33 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.