Re: MK14 schematic revisions
 

Thats a much better option. I wish id seen those when i was buying parts. I will get some when i have the money for when i get my stuff back and start building mine!

Re: MK14 schematic revisions
 

My offer applies to you as well if you want me to add any onto my next Farnell order. Just send me a pm.

Re: MK14 schematic revisions
 

As a matter of interest I ordered three of those 1" by 20-way strips from Farnell today, so I'll let you both know if they are as suitable for the job as they seem when we get them.

Re: MK14 schematic revisions
 

I have also ordered 10 TIL 393-3 Displays as Slothie suggested so between us we may be able to make some displays up!

Re: MK14 schematic revisions
 

Hmm I should dell some of my toilet roll stockpile and panic buy displays instead!!

Re: MK14 schematic revisions
 

The flexy strips from Farnell arrived and they are perfect as MK14 display ribbons, they are quite stiff but stay posed in any shape you bend them into, just like the originals.

Tim, I'll send one down to you with the 7408s, although I expect you will probably fit a pin row connector in your second MK14 to facilitate connection of a larger display for demo purposes.

Slothie, I'm not sure if you are between premises, anything sent to your current residence will probably just get lost in the system - I'll keep the remaining two here for now - I will use at least one myself anyway.

I now also have a full set of sockets - actually had to order 18 and 40 pin sockets in because we no longer use 18-DIP or 40-DIP ICs in anything we make at work. A depressing sign of the times.

Re: MK14 schematic revisions
 

Thanke, its going to be months before i get moved and enough stuff from storage to start buildung anything! As it happens all my post is redirected to my sister in Essec at the moment while she looks after my affairs! Farnell seem to have a reasonable stock at the moment so unless thetrs s rush on them I should be able to get one for each of the displays I have.
I'm glad you spotted these because when I was looking for a solution I completely missed these and ended up with the Spectra strip which works fine but is a real pain to strip neatly and tin so it goes into the board holes nicely. Its also rainbow striped because Farnell no longer stock the grey stuff in 0.1" pitch.

Re: MK14 schematic revisions
 

Actually, GrahamN flagged those up. I did find these which are also potentially of interest, although expensive for what they are:-

https://uk.farnell.com/samtec/ids-18...way/dp/2018235

You could probably use the manufacturer brand and part number to find them considerably cheaper elsewhere.

Two of these combined with Slothie's 0.1" pitch 'Spectra Strip' ribbon cable would make a nice display extension cable, assuming both the PCB and the display were fitted with 18-way male (pin) connectors - useful if you have ambitions to put a replica PCB into some sort of enclosure with the display extended to a window on the enclosure.

Of course you'd have to extend the keypad to the enclosure as well but unlike the display, a remote mounted keypad is already provided for via the keypad connector on the right hand side of the PCB.

Re: MK14 schematic revisions
 

Interesting! Good job the PCB is drilled for .1" square pin headers which i presume those connectors go onto. :)

Re: MK14 schematic revisions
 

Indeed they do. Work acquired me several 'samples' to play around with, actually.

Re: MK14 schematic revisions
 

Hi
Just to say that I managed to get my MK14 working using the PCB from Martin.

I started up for a while but now the display has stuck and just display 1 digit. Not sure but suspect one of the old chips on the board might have failed. Well being stuck in doors at present means I should have time to check it out.

David

Re: MK14 schematic revisions
 

One very bright digit?

Most common reason for that is the PCB stuck in (or held in) reset as you get the same effect when the machine is working and you hold down the reset button.

Don't run it that way for too long because the single display which is lit may get cooked - in normal operation each display is only lit for less than 1/8th of the time.

Also - if you have a logic probe or scope, check the clock oscillator is running.

One (unlikely) cause of this problem is that the reset circuit capacitor may have been inserted with the wrong polarity - if so it would probably work at first and then begin reverse-leaking, which would have the effect of holding the PCB in reset. Just a thought.

Re: MK14 schematic revisions
 

... More parts gathered. I have been aware for a while that these might be somewhere to be found, but, with this new-build MK14 now lacking only a PCB and some RAM I thought it might be wise to find them if possible and reserve a set in appropriate colours. I've placed them into a piece of perforated board so they are laid out more or less as they would be, with the black tops for command keys, red for 0-9 and blue for A-F.

I believe these switches - in particular the red ones - are the exact type which was supplied as the reset switch for the original MK14 kit. The rough 'crackle finish' on the button surface might make them quite difficult to legend with Letraset or similar - may have to polish them smooth first.

Before then, though, I'll need to make sure the PCB can accept them. They fit into a 0.1" matrix, the pins are 0.2" apart from each pin to the two nearest other pins. They would almost certainly fit straight into an original or replica issue V MK14 but I have a feeling the pins spacing on Slothie's PCB will be smaller as it is laid out for tact switches. If I can work out how to measure the distance between two points on a PCB in Kicad, I'll try to look at this later.

Re: MK14 schematic revisions
 

Sadly I dont think they will fit as the pcb is designed for 12mm tact switches or 9mm metal domes. I thought about the D60 switches instead of the domes but never got round to updating the footprint.

Re: MK14 schematic revisions
 

You are right, having looked, the footprint of the tact switches is not square like those of the rescued switches. I'll hang on to them in case I ever come into possession of an issue IV / issue V PCB.

Re: MK14 schematic revisions
 

These switches might well fit into the PCBs provided by j m precision, which is currently on ebay - look for MK14.

Hope everyone is okay in these difficult times.

Cheers :beer:
David

Re: MK14 schematic revisions
 

I actually have an original issue II MK14, so no need for one of the JM ones here - I'm aiming to build one of Slothie's because his PCB has features which no other one has.

How are you getting on with that fault on your Czech PCB?

Re: MK14 schematic revisions
 

Hi
No luck so far - checked the reset circuit that looks fine, checked and the crystal ciruit seems to be workings. Replaced a couple of the chips I had spares for but no luck.
I think I need to check that the Roms are working - here comes another Aduino circuit to read them.

Thanks for the warning on the display but I've had to build my own one and it can take being on all the time. ( see picture )

Of course pulling the bits from my MK14 I also found my NASCOM2, Spectrum and ATARI machines - all fun to play with,

Cheers
David

Re: MK14 schematic revisions
 

I like it! I think Tim(bucus) here has acquired or at least ordered a quantity of compatible calculator type displays - not sure if he needs them all. (Tim?)

If you have doubts about the PROMs you can lash yourself up an eprom-to PROM adaptor like the one in the attached image #1, program something like a 2716 with the OS code and see if it does / does not work.

I've also already written an Arduino PROM reader, this was to help out someone over on the vintage computer forums who had a suspect SCMPKB PROM in a National Introkit. That device is 8-bit wide but the sketch will read your 4-bit PROMs if you wire them side by side with the address pins and chip selects commoned. Example of output from the reader in attached image #2.

Arduino sketch for the reader is attached wrapped up in a .zip, as .ino is not a valid attachment in this forum. The Arduino pin connections to the PROM pins are given in the comments. It was written for an UNO.

It's quite crude, it sends its output as tabled ASCII Hex to the built in serial terminal in the Arduino IDE. It also calculates and displays the 16-bit checksum of the PROM code which is handy if you know what it should be.

Re: MK14 schematic revisions
 

One word of caution though, those little Bipolar PROM devices are quite thirsty. The PROMs on my MK14 account for nearly half of the 0.5A it draws from 5V. I'm not certain if the 5V output on the UNO can source that much current.