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

Buzby123 3rd Sep 2020 5:37 pm

I found it! A very sorry looking MK14.
 
5 Attachment(s)
Deep in a long lost corner of my attic, I found my MK14.

Time has not been kind to it, and it looks like I was not so kind to it either, back in the day.

I can recognise the cassette interface, and the board I built to drive the new display.

The board near the cassette interface looks a bit like a D-to-A resistor network, and it has a pair of wires to two ( of the many ) unlabelled sockets on the front.

I've no idea what the battery-backed circuit is for. It's got two NMC6514 1k x 4 RAM chips on it, so maybe I had a non-volatile RAM somewhere in the memory map.

The display board is from 'Sintel' ( who remembers them ? ) with 8 FND507 LEDs, I think.

The MK14 itself is an Issue 2 board, so that explains all the wiring on the back. The chopped-off ribbon was to my VDU sprite board, long gone now.

The three un-marked switches need some tracing. One is probably 'single step'. but I've no idea what the others are.

As you will notice, there are two mains transformers - because you can never have enough uninsulated 240v connections in your aluminium enclosure.

Am I going to plug it in ?. No way !.

The case is full of a white powdery substance, and it's got everywhere. I'm going to photograph everything, then take the boards out, clean up the white stuff, and then start on the MK14 board alone.

I've got plenty of spare parts, but not a lot of time just yet. It's going to be a while before Micky sings again !.

Cheers,

Buzby

SiriusHardware 3rd Sep 2020 5:54 pm

Re: I found it !. A very sorry looking MK14
 
That looks like a really good 'real life' MK14, very typical of the sort of things which would have been done back then. I bet it looked really smart when it was all fresh and new.

For a long time mine (also issue II) had the display and keypad extended off board and it was fitted in various enclosures, the neatest of which was an executive-style briefcase complete with a set of 'D' batteries which would run it for a few hours.

In the noughties I embarked on a process of restoring it to more or less original single-board configuration, although the original keypad was long gone by then.

SiriusHardware 3rd Sep 2020 6:36 pm

Re: I found it !. A very sorry looking MK14
 
I'm thinking the white powder may be fallout from the NiCad? NiMH? rechargeable battery.

I would get rid of, or at least replace that at the earliest opportunity, as we have seen terrible damage wreaked upon otherwise well preserved systems - not MK14s, but other retro systems like the Amiga A500, by decomposing rechargeable batteries.

I have a 'Maplin Z80 system' which had been in beautiful condition, but the PCB mounted NiMH battery started to out-gas some sort of vapour while it was in storage: A lot of the IC pins turned malachite green and the pristine white screen printing just drifted off the PCB like confetti when I tried to blow the white 'snow' off the PCB.

Buzby123 3rd Sep 2020 6:40 pm

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

Originally Posted by SiriusHardware (Post 1285863)
That looks like a really good 'real life' MK14 ...

Yes, this one had a really good life !.

It's had just about every gadget under the sun plugged into that breadboard, and the main board has been modified no end.

It even had a role in factory life !.

We were installing PLCs in a synthetic fibre plant. We had been told the fast IO cards we needed were on 6 weeks delivery, but it was really 6 months.

To get the plant running in time, I programmed the MK14 to take the fast signals from the plant, and replay them to the PLC a a slower rate.

This is the machine I cut my programming teeth on, and it was fun !.

Very soon after I moved on to Acorn System 1, then Apple ][, and they were fun as well.

Now I've got Arduinos and rPis, but no inclination to do anything with them.

Cheers,

Buzby

SiriusHardware 3rd Sep 2020 6:50 pm

Re: I found it !. A very sorry looking MK14
 
It has been argued here that the MK14 was really the Arduino of its day - although it never had 'Flash memory' as such, you could buy the optional PROM programmer and burn project-specific firmware for it so that it would instantly do that job as soon as it was turned on, much like an Arduino which has been programmed with a 'sketch'. Yours of course had (rather rare) nonvolatile program storage so yours could have been used in a more Arduino-like fashion than most.

I've heard of one case (only) where MK14s were apparently used as dedicated controllers in stage / venue lighting equipment, but unfortunately I don't have the name of that specific product. There may be a few 'embedded' MK14s still around awaiting to be discovered in the back rooms of old clubs or theatres.

The Pi and Arduino both provide handy ways of 'typing' code into the MK14 at fairly high speed, so they have their uses.

Buzby123 3rd Sep 2020 6:53 pm

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

Originally Posted by SiriusHardware (Post 1285876)
I'm thinking the white powder may be fallout from the NiCad? NiMH? rechargeable battery.

No, and yes.

The battery is NiCad, and it is going a bit green, but the white stuff I think is something completely different - concrete effloresence. ( Don't ask ! )

Cleaning this up is going to be my first task. ( If I took the MK14 out and did that first, I would think 'Job Done', and it would never get back in its box again. )

Cheers,

Buzby

SiriusHardware 3rd Sep 2020 7:02 pm

Re: I found it !. A very sorry looking MK14
 
We look forward to seeing the end result, as and when you have to time to get to it of course.

Andrew2 4th Sep 2020 8:14 am

Re: I found it !. A very sorry looking MK14
 
I'd love to know what that sheet music is....:thumbsup:

Buzby123 4th Sep 2020 8:24 am

Re: I found it !. A very sorry looking MK14
 
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It looks like I was trying to get Micky to play Cwm Rhondda.

SiriusHardware 4th Sep 2020 8:41 am

Re: I found it !. A very sorry looking MK14
 
That tune appears polyphonic (more than one note at a time) so good luck with that! Although, there were some games for the Spectrum which managed polyphony over the Spectrum's single digital audio output - 'Fairlight' springs to mind.

I have toyed with the idea of adapting 'Music Box' to play its output over MIDI, since I have several MIDI equipped synths here. The original tune in the manual is 'God Save The Queen'. I think that would sound quite good on distorted electric guitar, Hendrix style.

Who will write the first MK14 'tracker'? :)

Timbucus 4th Sep 2020 4:43 pm

Re: I found it !. A very sorry looking MK14
 
That is a wonderful looking machine - as you say it cries out to be restored 'as is' . If it was mine I suppose the only 'mod' I would make would be to cut and fit a perspex window and white LED lighting to show off that lovely White CERAMIC SC/MP and reveal part of the cleaned up MK14... - very unusual.

Thanks for sharing and look forward to see the cleaned up result. As Sirius says a small hidden PI0W would allow it to be used for wireless uploading of programs easily using his programmer which could just be wired in parallel with the MK14 at no risk as it uses Opto Isolators.

Cobaltblue 4th Sep 2020 5:31 pm

Re: I found it !. A very sorry looking MK14
 
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I just dragged this one out of the bungalow I don't recognise the knitting so it might be one I acquired on the way as far as I remember mine ended up as a EPROM programmer and it's not turned up yet!

Cheers

Mike T

Timbucus 4th Sep 2020 5:48 pm

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

Originally Posted by Cobaltblue (Post 1286167)
I just dragged this one out of the bungalow I don't recognise the knitting so it might be one I acquired on the way as far as I remember mine ended up as a EPROM programmer and it's not turned up yet!

Cheers

Mike T

Nice one - full memory and an 8154... thanks for sharing and nice to know there are other MK14 owners/users around here.

SiriusHardware 4th Sep 2020 5:55 pm

Re: I found it !. A very sorry looking MK14
 
Cobaltblue (and Coolsnaz2, who posted in the VDU thread) are both very fortunate to have genuine examples in such good original condition with the keypads still intact, as the original keypads were so 'eccentric' that they were usually replaced with something better as soon as possible.

Buzby123 4th Sep 2020 7:36 pm

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

Originally Posted by SiriusHardware (Post 1286173)
... the original keypads were so 'eccentric' that they were usually replaced with something better as soon as possible.

'Eccentric', that's a very diplomatic way of saying 'total crap'.

As an aside, I have another computer with a non-original keyboard ....

Buzby123 4th Sep 2020 10:38 pm

Re: I found it !. A very sorry looking MK14
 
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I've unplugged the daughter board, just to see it a bit better.

It looks like my Micky needs this board to run. IC16 on the main board has been removed, and some pins on two of the 2111s have been bent up and wired to the daughter board. I think there is a lot of address decoding which is now on the daughter board.

Also, there are two 74S571 chips on this board, and two still on the main board.

It's coming back to me through the mists of time, I think the toggle switch near the red button would let me select 'old' or 'new' ROMs. ( Don't ask me why I thought this was a good idea, it was a long time ago. )

This is one seriously hacked MK14, I must have been really enthused to have put so much effort into it.

One thing I am missing is documentation. ( I might find it, but I'm not holding my breath. )

Does anyone have a link to an Issue 2 schematic ?.

Cheers,

Buzby

Timbucus 4th Sep 2020 10:53 pm

Re: I found it !. A very sorry looking MK14
 
I have never seen an Issue 2 diagram anywhere online - I have a very grainy lo res Issue 4 captured from an e-bay listing and one I do not know that just says "originalSchematic.jpg" which I think is Issue 3 a slightly fuzzy version is at: https://www.old-computers.com/museum...Diagram_s1.jpg

SiriusHardware 5th Sep 2020 8:49 am

Re: I found it !. A very sorry looking MK14
 
I still have all the original documentation which came with my issue I I but you've caught me at a bad time as I am away from Tracy Island just now. The most widespread diagram online is that of the issue II as far as I know, it was always much harder to find the one for the issue V.

If you haven't found it in a week or so remind me and I will scan mine.

Slothie 5th Sep 2020 3:08 pm

Re: I found it !. A very sorry looking MK14
 
This is a link to a copy of the MK14 manual for early versions of the MK14 including the schematic. It documents the "original" monitor that resets to "---- --" as well as the schematic showing the PROM decoded only by the A11 signal, as was the case with early boards.

https://drive.google.com/file/d/1C32...ew?usp=sharing

I'm pretty sure I've got the sharing options correct....!

Buzby123 5th Sep 2020 7:46 pm

Re: I found it !. A very sorry looking MK14
 
Thanks for the manual, it's brought back a lot of memories.

Tomorrow I'm starting to fettle the case.

First I need to photograph every connection, as already a couple of wires have come loose.

Then de-solder and remove the transformers ( Still can't remember why I've got two transformers. I think the second one is for a +ve and -ve supply to a 741 op amp. )

Then remove all the circuits from the bottom and sides. Then I can give it a good wash.

That big electrolytic is dated 1974, will it need replacing ?.

Cheers,

Buzby

Slothie 5th Sep 2020 8:36 pm

Re: I found it !. A very sorry looking MK14
 
Its probable the electrolytic will need re-forming at very least if its not been used in years.
Connect an incandescent bulb (e.g.12w 12v bulb from car) in series with the cap and connect to a suitable power source (could even be the transformer/rectifier you already have). If the capacitor is still passing a significant current after a few minutes then its probable the electrolytic is toast. Leave the capacitor connected for several hours to allow the oxide film to re-form before removing the bulb. Its probably worth checking the current with a meter too - with no load there should only be a small leakage through the capacitor. With the transformer switched off and no load the voltage across the capacitor should fall fairly slowly.

Buzby123 6th Sep 2020 3:01 pm

Re: I found it !. A very sorry looking MK14
 
2 Attachment(s)
Progress so far ...

Circuit boards and transformers removed from bottom of case, bottom case given a thorough scrub with foaming cleaner, and a rinse. Still stained, but stable. No flakey bits.

Refitted main transformer, checked 240v wiring, refitted combined PSU and DAC board. ( Why on earth did I put these two on the same board ?. And why did I do most of the wiring with bell wire and 4-core telephone cables ? )

Powered up. No smoke, sparks, buzzes or bangs, so it's probably OK. ( or totally dead !)

Smoothed supply is 12.8v, regulated is 4.96v, so the TO3 regulator thingy ( I can't remember the number ) is looking OK. I'll leave this running for a few hours, and move on to the case top.

First thing to tackle is the keyboard.

Question number 1, can these keytops be 'popped off' and refitted ?.

Cheers,

Buzby

TonyDuell 6th Sep 2020 3:54 pm

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

Originally Posted by Buzby123 (Post 1286673)
First thing to tackle is the keyboard.

Question number 1, can these keytops be 'popped off' and refitted ?.

Cheers,

Buzby

Those look like a keyboard switch that RS sold many years ago. The coloured buttons do come off without damage (they fit onto a sort-of cross shaped black actuator in the main body of the switch)

Actually RS still sell a siimilar switch, but without the cap :

https://uk.rs-online.com/web/p/keybo...tches/7931712/

They also still sell the switches to solder to later verson MK14 boards in place of the keypad.

Buzby123 6th Sep 2020 4:26 pm

Re: I found it !. A very sorry looking MK14
 
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Thanks for the info.

I remember now, I did get them from RS. Now I can get them re-Letrasetted, but this time I'll put some lacquer on as well.

The numbering wore off while I was still using using the machine, 40 years ago, but it didn't bother me. The layout of that keyboard is burnt into my brain !.

Cheers,

Buzby

Buzby123 6th Sep 2020 5:15 pm

Re: I found it !. A very sorry looking MK14
 
Here's a question with no right answer, but I'd like your views.

When I get Micky working again, should I repaint his case like new, or leave it as is ?

Slothie 6th Sep 2020 5:34 pm

Re: I found it !. A very sorry looking MK14
 
Personally, unless after cleaning it looks really tatty then I'd leave it. A few scratches and scuffs have been earned :)

Timbucus 6th Sep 2020 6:29 pm

Re: I found it !. A very sorry looking MK14
 
I think if you were to fit it with a repro board and use it actively again (restoring the MK14 as a standalone unit) it would be OK to paint it. If you intend it to house the original still then it should be left as is - that is what any museum would do after stabilizing the paintwork to prevent further degradation. As Slothie says the history of a piece is written in the wear it has received until the point it is preserved and ceases to be a daily used item.

SiriusHardware 6th Sep 2020 7:11 pm

Re: I found it !. A very sorry looking MK14
 
The buttons for those switches are still stocked by digikey and their manufacturer part number is BTN MDP nn (Where nn is the 2-digit colour code).

See here.

https://www.digikey.co.uk/products/e...=1&pageSize=25

These are actually the type of switch and cap fitted to the keypad my MK14 has now, but at the time the caps were only available in red or blue so I couldn't have the command keys picked out in a third colour so I made the numeric keys red and the rest blue.

I keep thinking I should get a few slate grey ones and redo the command keys in that colour as I would have done originally. But then I think.. this has been the machine's keypad for most of its life... I shouldn't mess with it now.

Buzby123 6th Sep 2020 10:11 pm

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

Originally Posted by SiriusHardware (Post 1286736)
... but at the time the caps were only available in red or blue so I couldn't have the command keys picked out in a third colour ...

A third colour ?. Why did you need three ?.

My digits 0-F were in blue, and Mem,Term,Go,Abort in grey. That's all the matrix keys done. ( Actually, the 0 was grey, 'cos I was a blue short. )

Regarding my progress, it's hit a tricky part. The three banks of LEDs around the breadboard are there to show the states of the 8154 IO pins, and the flags etc. from the CPU. All these signals are from the long edge connector.

With no MK14 board in place there should be no LEDs lit, but some are. The LEDs are driven by simple transistor circuits, but getting at them is going to be difficult.

I must have fitted the LEDs and sockets first, then put the veroboard onto the pins of the LEDs/sockets, then soldered. This means I have to desolder all the sockets to remove the board. ( I can pop out the LEDs ).

It's obvious I thought they would never need fixing in the future. Isn't hindsight wonderful !.

Cheers,

Buzby

SiriusHardware 6th Sep 2020 10:30 pm

Re: I found it !. A very sorry looking MK14
 
One colour for 0-9, one for A-F and a third colour for the command keys.

That's just how I wanted it to be. There would be absolutely nothing wrong with all the caps being the same colour, as they are on the vast majority of keypads of all types, or the command keys being one colour and 0-F being another as they are on yours.

I would still consider redoing all of my key caps even now because at least 4-5 of the letraset legends are noticeably off centre. At the time I just wanted to get on with using it so I didn't do it as patiently as I would now, but the shoddiness of the job my teenage self did irritates me every time I look at it.

And yet, nothing dates a homebrew project to the mid-late seventies the way slightly wonky Letraset lettering does, so if I were to replace that with neater lettering done by my near 60 year old self, I would be destroying part of its authentic history.

The compromise would be to obtain a full replacement set of caps and re-letter them to my current satisfaction, but keep the original caps in a safe place so that the keypad could be restored to its genuine late seventies appearance if I ever felt the need to do that.

Buzby123 6th Sep 2020 11:14 pm

Re: I found it !. A very sorry looking MK14
 
I actually thought of having mine laser engraved, but then thought 'that won't look anywhere near original', so it's back to wonky Letraset !.

I'm seriously thinking of getting a repro board, not to replace mine, but to use as a known good system for testing this one. I've got enough CPUs and stuff to build the core of a repro ( with different display and no KBD ) and it would help with testing my chips. That daughter board is a nightmare as the main board won't work without it, so I won't know where any fault lies. Anything that gives me a stable starting point will help.

One thing I know will be 'wrong' when I get this working as it was 40 years ago, the display will be dim. My display driver circuit was dim from the day I built it, but it was good enough for me, so I never re-visited it. Today I would have no problem designing a replacement that performed better, but it won't be old-skool. Should I do it ?.

Cheers,

Buzby

SiriusHardware 7th Sep 2020 7:30 am

Re: I found it !. A very sorry looking MK14
 
Since we're both talking about third-party items we made ourselves (keypad, display driver), we may be being unnecessarily fussy. If both machines (yours and mine) were complete originals it would be borderline sacrilege to replace anything but when the items in question are uniquely of our own making, so who is to say that I did not originally do a better job of lettering my keys and you did not do a better job designing your display driver? (Well, anyone who reads this, I guess...)

If it had been possible at the time to obtain (and afford) a set of professionally legended keys, I would certainly have fitted them, and if you had known then what you know now your display would be brighter.

So again the compromise, I would say, is to replace what you don't like but preserve the original driver board in such a way that the change is reversible, and maybe try, in your case, to use components and materials in the new driver which are 'right' for the period and which could be taken to be the original driver circuit by anyone who has not seen it before. You could even use bell wire and strands of telephone wire for any necessary power and signal links, to make it blend in with the rest. :)

Buzby123 7th Sep 2020 9:47 am

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

The display driver looks like it uses a ULN2007 darlington array for the segments, and some kind of 1-transistor circuit for the anodes. The darlington has a 150R resistor array to the segments, that's not going to help !.

So it looks like I just need to change the resistor array for a start, and maybe replace the darlington with a MOSFET equivalent. Neither of these changes would need rewiring, just replace socketed chips. I'll investigate this later, I've got bigger fish fry at the moment.

Some of the 8 IO switches are a bit dodgy, I remember this from way back. I'm hoping I've still got a few spares, if not I'll have to replace them with a modern equivalent. I don't really want to do this, as I can't find any with the same toggle design. Those perfectly cylindrical covers are so 70's.

Anyway, I'm still working on replacing dead BC109s, all the while cursing my younger self for building such a servicing-unfriendly machine.

Cheers,

Buzby

SiriusHardware 7th Sep 2020 11:08 am

Re: I found it !. A very sorry looking MK14
 
Since your system obviously has extra RAM (over and above the standard full 640 bytes) you would have needed a hole somewhere in the memory map somewhere for that memory to drop into.

Only the final issue (Issue V) had that memory hole available as built. MK14 issues II to IV all had unwanted 'images' of the OS in the region 0200-07FF which first had to be removed before any new offboard memory could be mapped into that area, so some of that hackery on the underside of your MK14 PCB will be for that purpose.

In post #6 of this long running thread

https://www.vintage-radio.net/forum/...d.php?t=145663

there is an attached single page document which was sent to me by SOC (circa 1978) in response to my question to them about how to expand the memory.

The document doesn't actually describe how to add more memory, it describes the mods required to a specific revision of MK14 - possibly issue II - to remove the unwanted PROM images at 0200-07FF as a precursor to adding more memory.

Unfortunately the document describes the mods 'visually' (Cut this, link that) rather than at circuit diagram level, but if you look at yours and yours has those mods applied you can probably say those particular mods don't need to be undone in order to get the machine to work stand-alone with its onboard RAM, since all they should do is remove the unwanted PROM images.

Buzby123 7th Sep 2020 1:01 pm

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

Yes, I remember doing that cut to the 'Y' track back in the day, but I think that must have been just the start of my hacking.

On my main board IC16 is totally removed, and two legs on my 2111s have been bent up and soldered. The daughter board has two 6514s, two 571s, two LS32s, a 7400, a 74LS14, and a 7493.

I can understand there would be a need for gates, but what is that last chip doing ?. It's a counter.

When I eventually get to power the full system, if it doesn't work as expected, then I'm going to have to trace the circuit on the daughter board. It's all Verowired, a real nightmare !.

It will not be soon though. I've got the IO lamps & switches, the display, and the keyboard to test and/or fix.

Cheers,

Buzby

Slothie 7th Sep 2020 2:14 pm

Re: I found it !. A very sorry looking MK14
 
1 Attachment(s)
Its probable the 7493 is being used in a single step circuit; although the circuit in the V1 manual uses a MC14024 counter, later issues shows a 7493A being used:

Buzby123 7th Sep 2020 2:43 pm

Re: I found it !. A very sorry looking MK14
 
That looks promising. The 7400 on my daughter board has only two gates used, the other pins are not connected. I also remember fitting a switch for single-stepping, but I don't ever remember using it.

I'll certainly need the combined knowledge of this forum when I get closer to running the board.

Thanks for your help,

Buzby

Buzby123 16th Sep 2020 11:51 pm

Re: I found it !. A very sorry looking MK14
 
1 Attachment(s)
I've started on waking Micky from his 40 year hibernation.

Because there is no easy access to the main board while it is in the case, I've taken it out and will work on it with no keyboard or display. I should be able to check enough signals with my scope to see if it is working.

When I was looking at the edge connector I noticed that Pin 8 was not connected to 0v, it is connected to NADS.

My board has 'MK 14 ISSUE II' printed in the copper, so I think it is an issue 2. But edge pin 8 connected to NADS is an issue 3 feature, according to the manual posted earlier.

I don't think this will make much difference to my task. I've hacked the board so much that it won't match any drawing that SOC produced !.


One question, are the PROMs likely to be OK ?

Cheers,

Buzby

SiriusHardware 17th Sep 2020 12:23 am

Re: I found it !. A very sorry looking MK14
 
1 Attachment(s)
The PROMs are bipolar fusible-link PROMs and there are anecdotes to the effect that that particular type of PROM can fail due to the micro fine wire fuses re-growing and making contact again.

I certainly have come across a few cases where bipolar PROMs have died. However, there's no reason to assume they are dud without due cause.

If you have a conventional EPROM programmer you can lash up an adaptor to read a pair of 4-bit wide PROMs as though they are a common EPROM. This sketch (attached) illustrates just such an adaptor to allow a 32 by 8 bit PROM to be read by an eprom programmer which thinks it is reading a 27256.

Just make a version of this which places the MK14 PROMs side by side so that the low nibble and high nibble are read out as one byte, common up the address lines A0-A8 and limit the address range being read by the eprom programmer software to 0000 - 01FF (512 bytes).

The attached drawing shows only A0 to A4 connected because the device in the example was a 32-byte device, you will obviously need to connect A5 through A8 as well, in order to read 512 bytes of memory.

My MK14 is also issue II and I've always just taken SOC's word for it that NADs was not introduced on the edge connector until issue III. I'll have to check that when I next have my original machine down for any reason.

Buzby123 17th Sep 2020 9:26 am

Re: I found it !. A very sorry looking MK14
 
1 Attachment(s)
I'd forgotten how poor these SOC drawings are !

SiriusHardware 17th Sep 2020 9:41 am

Re: I found it !. A very sorry looking MK14
 
You're referring to the missing 'interconnection' blob on the junction of Read Data / IC7 OE / IC17 input, I take it. Yes, quite poor.

Also the misleading way in which the connections for the external keypad connector are shown, as they do not arrive at the edge connector in the order that the circuit diagram suggests they do. The addition of some pin numbers to the drawing of the keypad connector would have been very helpful.

Slothie 17th Sep 2020 10:37 am

Re: I found it !. A very sorry looking MK14
 
I "corrected" that blob without really noticing it because I had already decided the schematic was more a guide than a definitive reference :) One version of the schematic I used had the numbers for the common cathodes of the display backwards and guess which one I followed on my initial prototype! So when I finally got my prototype working the display was fully working and backwards! Much track cutting and bodge wire fitting followed that one.
All things considered its a wonder I got the keyboard connector correct as I seem to have done. I think its because by then I was using an issue V schematic I'd found and confirmed it with posts I'd seen on here (possibly your MK14 uploader device). Because the schematic was so vague I had to go looking elsewhere...

SiriusHardware 17th Sep 2020 10:55 am

Re: I found it !. A very sorry looking MK14
 
I am fairly convinced that this was why the JMP replica PCB ended up with a different (and arguably more logical) order of keypad connections. If the originator didn't have an original PCB to trace from it would have been perfectly reasonable to take the diagram at its word.

But yes, you got the keypad connector right, as you did with so many other things.

Buzby123 17th Sep 2020 12:13 pm

Re: I found it !. A very sorry looking MK14
 
3 Attachment(s)
I'm beginning to think it would be easier to design and build a new MK14. This hacked board of mine is giving me grief.

I've taken the 8154 out, and swapped the ceramic 8060 for a plastic one, just in case I make a slip.

Powered up, drawing 0.42A, looks OK. Clock is running, 8060 data lines all wiggling about. DB0-3 solid 0-5v, but DB4-7 show some 'half-way' levels. Not too worried about them yet.

Most address lines on 8060 look reasonable, but AD09,10,11 don't look happy at all.

I now need to find where these go. The SOC drawing is no use, because I completely re-hashed the address decoding, and most of it is now on that verowired daughter board !.

Wish me luck !.

Cheers,

Buzby

Slothie 17th Sep 2020 12:57 pm

Re: I found it !. A very sorry looking MK14
 
Its worth noting that on the MK14 only D0..D3 have pullups to +5v, so when the data bus goes tristate D0..D3 will go to +5v but D4..D7 will do whatever they like. Something else on the bus may be pulling these lines weakly to odd levels, or capacitive coupling or........

Buzby123 17th Sep 2020 1:15 pm

Re: I found it !. A very sorry looking MK14
 
Yes, that's why I'm not too bothered about the wobbly signals on D4-7.

But the AD09-11 pins should only have hi/lo, and that's what I'm going to try and sort out before going any further.

Unlikely I'll be doing any more today, other duties call.

Cheers,

Buzby

Slothie 17th Sep 2020 1:34 pm

Re: I found it !. A very sorry looking MK14
 
1 Attachment(s)
Disclaimer: I havent actually probed an MK14 with an oscilloscope recently
According to the data sheet the address lines are only driven while NBREQ is low, which is from just before NADS goes low to just after NRDS/NWDS goes from low-to-high; that means the address bus can be floating from (just after) the positive edge of NRDS/NWDS to (just before) the falling edge of the NADS.

Anyhow, its worth investigating and reverse-engineering your veroboard just to know what its doing!

Buzby123 17th Sep 2020 10:32 pm

Re: I found it !. A very sorry looking MK14
 
I didn't realise that the address pins were occasionally 'floating', so it seems like my screenshots might not be as bad as what they look like.

But are all the address lines being driven at any time ?. I don't what areas the code is accessing.

What I need now is the gadget I built a hundred years ago, the 'NOPulator' !.

This was a gadget I built when I was working for an arcade machine company, fault finding in things like Space Invaders and pinball machines.

Finding faults in the address decoders was a PITA, until I built the NOPulator.

This was a Z80 CPU mounted on a 40 pin DIL, which plugged in where the original Z80 should be.

The Z80 on the NOPulator had it's data pins 'bent up' and they were hard-wired as a NOP. This made the Z80 run through the whole address range repeatedly, executing NOPs at every memory location.

A tiny switch gated the RDstrobe from the Z80 to either RD or WR on the socket, so the NOPulator would either read or write the whole memory range.

What I need now is a NOPulator based on an 8060.

Mark1960 17th Sep 2020 11:14 pm

Re: I found it !. A very sorry looking MK14
 
Rather than bend pins on an ins8060, try removing the proms and ram, then add pullups for the data lines that donít already have them. Should run CAD instruction using auto index P3 which should then cycle through memory, every third access should read from an out of sequence location but maybe not too hard to check the pattern.

SiriusHardware 17th Sep 2020 11:20 pm

Re: I found it !. A very sorry looking MK14
 
1 Attachment(s)
The hex code for NOP in SC/MP is 0x08, so in theory you can make something which will apply that hex code to the data bus all the time or just during _NRDS and the CPU should just sweep majestically through the address range executing all the NOPs.

You'd need to remove anything else which might try to place data on the bus in response to a read from any part of the address range - RAMs, PROM, etc.

If you make a breakout adaptor from a standard EPROM or EEPROM pinout to 2 * 16 pin headers to plug into the PROM sockets you can try writing little bits of test code to exercise various parts of the circuit to see if they behave as expected.

Like this: I have this one programmed with the 'Old' OS and 'New' OS, selectable, so I can run tests with either OS. I used ordinary 16-pin IC sockets as the 16-pin 'header plugs' which plug into the PROM sockets.

Edit: Cross posted with Mark.


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