MK14 - New replica build

[Roninfourseven]

OK, I was away at the weekend but had today off, so I finished the cassette interface. I do need to just do a sanity check by buzzing it all out with my multimeter, but I gave it 5v earlier and no smoke do that seems positive. Pictures to follow, it's all point to point wiring so a bit mad

[SiriusHardware]

I'll be too far away to hear the bang, but I'll get my seismometer ready.

[Roninfourseven]

Originally Posted by SiriusHardware

I'll be too far away to hear the bang, but I'll get my seismometer ready.

[Roninfourseven]

OK, so here is the cassette interface, but due to being a bit busy I've just not got around to testing as yet.

Once I know it works I'll put solder mask over the back to prevent shorts. It was fun doing all the point to point wiring!

I'm also waiting on an edge connector so I don't have to connect directly to the pcb, which I'd prefer not to do.

[SiriusHardware]

Good job, fingers crossed it works for you after the time you've obviously spent on it.

Several of us have soldered 64-way (2 x 32 way) DIN 41612 'card' connectors edge-onwards to the MK14 rear connector, with one row of pins laid flat along the top side edge connector connections and soldered to those, the other row of pins laid flat against the lower side edge contact connections and soldered to those. You might also want to consider that.

It's not very original, but it is a lot safer because the matching connectors can only be plugged in one particular way around and one way up. If you do that as well, try to keep in mind the possibility that you may at some point add a VDU, because the VDU connector can only practically go onto the VDU board one particular way around and the connector you put on the MK14 needs to be the same way up to mate with it.

That said, all my MK14 add-ons have the traditional slide-on 0.1" pitch edge connectors, the reason being that one of my MK14s is a real one and I don't want to solder anything to it or modify it in any way.

[Roninfourseven]

Originally Posted by SiriusHardware

Good job, fingers crossed it works for you after the time you've obviously spent on it.

Several of us have soldered 64-way (2 x 32 way) DIN 41612 'card' connectors edge-onwards to the MK14 rear connector, with one row of pins laid flat along the top side edge connector connections and soldered to those, the other row of pins laid flat against the lower side edge contact connections and soldered to those. You might also want to consider that.

It's not very original, but it is a lot safer because the matching connectors can only be plugged in one particular way around and one way up. If you do that as well, try to keep in mind the possibility that you may at some point add a VDU, because the VDU connector can only practically go onto the VDU board one particular way around and the connector you put on the MK14 needs to be the same way up to mate with it.

That said, all my MK14 add-ons have the traditional slide-on 0.1" pitch edge connectors, the reason being that one of my MK14s is a real one and I don't want to solder anything to it or modify it in any way.

Thanks for the info, I'll have a look at what the options are once I have the edge connector. I totally understand what you mean about correct orientation and even though mine is a replica, I still don't want to kill anything, especially as some of the IC's are quite expensive, and I don't like the idea of soldering to the board, it's just messy IMHO.

[Roninfourseven]

Well, my edge connector finally arrived!!! Unfortunately I'm in the middle of refurbing a Colecovision, so further messing around will be done when I can fit it in around that, but at least I have it now.

[SiriusHardware]

Thanks for the update.

Is your connector exactly the right type (double sided, 32 + 32 way, open ended) and if so do you mind my asking where you got it from? I only have one unallocated spare one at the moment.

[Roninfourseven]

Originally Posted by SiriusHardware

Thanks for the update.

Is your connector exactly the right type (double sided, 32 + 32 way, open ended) and if so do you mind my asking where you got it from? I only have one unallocated spare one at the moment.

It's not open ended, my intention is to open one end which will effectively ensure it can only be fitted one way.

I got this: https://www.ebay.co.uk/itm/385285944810

Took a good two weeks to arrive though as it came from China.

[SiriusHardware]

Ah, I guessed due to the time delay it had probably come from China. When my original 'MK14 revival' kicked off in around 2012, when I decided to dust mine off and play with it again, RS were still stocking two 'cinch' edge connectors which were exactly the right type for the rear connector and the keypad connector - they had stopped stocking the 32 + 32 way one the last time I checked, and I doubt whether they will still do the keypad connector one by now.

Leaving one end closed, if the dimensions allow it, will make it easier to line up first time every time - it's a pity SOC didn't opt for an edge connector with a locating 'key' in place of one of the contact positions, as they did with the ZX machines.

[ortek_service]

Originally Posted by Roninfourseven

It's not open ended, my intention is to open one end which will effectively ensure it can only be fitted one way.

I got this: https://www.ebay.co.uk/itm/385285944810

Took a good two weeks to arrive though as it came from China.

Thanks for the link.
They're surprisingly quite-expensive, coming from China.
Although at least delivery is free (but you don't get much discount for higher quantities).

I do have lots of Spectrum (Rotronics Waferdrive long-pin with bracket specials), I got as surplus. But annoyingly, these are a bit too short for expansion connector, as only (2x) 28way.
Although I have picked-up from rallies etc over the years numerous Blue & Green etc Coloured Vero & RS ones, so I may have one I can cut-down a bit.
IIRC, I did find one the right-size for the Keypad connector, that only needs to be a single-side one.
But may need to cut one-end open, on the fully-enclosed ends types.

[Roninfourseven]

@SiriusHardware & @Ortek_Service.

I had time over the weekend to file down one end of the connector and it worked out very well as you can see from the pictures.

The closed end allows for correct alignment every time and prevents incorrect connection, plus the contacts line up very nicely top and bottom.

A locating key would have been nice, but it is what it is I suppose. I guess if the key was at the end I'd filed off that would still have left it open for reverse connection, so a more Spectrum like key would have been better to be 100% sure.

I agree, the price was a bit expensive, but with free postage it was tolerable

[SiriusHardware]

Good going - now we need suggestions for the best / neatest way to open up one end of an edge connector which originally has two closed ends. I gather you just filed away one of the closed ends square-on until it wasn't closed any more?

Last one I tried to do I tried it with a scalpel blade, but the carrier was made from amazingly hard material. I still haven't found the rest of the scalpel blade - It probably ended up embedded in one of the ceiling tiles after only narrowly missing me on the way up.

That Traco SMPSU replacement for the 7805 is really tiny - do they get warm at all?

[Roninfourseven]

Originally Posted by SiriusHardware

Good going - now we need suggestions for the best / neatest way to open up one end of an edge connector which originally has two closed ends. I gather you just filed away one of the closed ends square-on until it wasn't closed any more?

Last one I tried to do I tried it with a scalpel blade, but the carrier was made from amazingly hard material. I still haven't found the rest of the scalpel blade - It probably ended up embedded in one of the ceiling tiles after only narrowly missing me on the way up.

That Traco SMPSU replacement for the 7805 is really tiny - do they get warm at all?

Yes, I just filed it down with a large flat hand file. There's no reason you couldn't do the bulk of it with something like a Dremel, but to be safe and sound I think finishing off by hand is the safest option. TBH it only took 5 or 10 minutes to file down by hand so not much of a hardship.

The Traco is very neat, I also just installed one in a Spectrum I repaired, and they run pretty cool, way cooler than a 7805 that's for sure.

As for your scalpel blade, I can only suggest that eye protection is a worthwhile investment!!!

[SiriusHardware]

Don't I know it.

So when's the big day? (when will you connect it up and give it a go?)

BTW one further hint, if your connector is anything like mine the female square ended receptacles on 'Dupont' jumper leads will be a nice snug fit onto the bare pins of the edge connector, if it's the same for you you can use that one edge connector for many things without ever soldering anything to its pins - just put 'Dupont' compatible pin row connectors on whatever peripheral you are intending to connect up - in this case your cassette interface - and use Dupont jumper leads to make the connections between the two.

I also find that SIL socket connectors can be pushed onto the bare pins of the edge connector so that I can wire up anything I use quite often by soldering its wiring to the pins of the SIL connector which can then just be pushed onto the bare pins of the edge connector.

Example of this attached.

[Roninfourseven]

Originally Posted by SiriusHardware

Don't I know it.

So when's the big day? (when will you connect it up and give it a go?)

BTW one further hint, if your connector is anything like mine the female square ended receptacles on 'Dupont' jumper leads will be a nice snug fit onto the bare pins of the edge connector, if it's the same for you you can use that one edge connector for many things without ever soldering anything to its pins - just put 'Dupont' compatible pin row connectors on whatever peripheral you are intending to connect up - in this case your cassette interface - and use Dupont jumper leads to make the connections between the two.

I also find that SIL socket connectors can be pushed onto the bare pins of the edge connector so that I can wire up anything I use quite often by soldering its wiring to the pins of the SIL connector which can then just be pushed onto the bare pins of the edge connector.

Example of this attached.

I'm just in the middle of refurbing a Colecovision, so it'll be a few days before I get it hooked up, as whilst I have just repaired the CV, there was a dead 4116 RAM IC picked up by my therrmal camera, I still have a few other things to do before my bench is clear, like sort out composite.

I'll have a look see if the DuPont connectors will fit, I'd like to be able to just plug and play like you do. I may have some spare SIL connectors I can try as well, thanks for the info.

I did also consider soldering the connector to a PCB to break out the connections but I don't think I have anything suitable to hand.

BTW can I ask what display that is and how you're driving it?

[SiriusHardware]

I don't know the display model number as that photo is quite a few years old, I just knew where to find it in another old thread.

The underlying controller IC on the display is the Hitachi HD44780 and that IC, or a clone of it, can be found in almost every one or two line alphanumeric (as opposed to dot-matrix) LCD display made for the last 30 years or so - the chip itself can address up to two 64-character lines but they are much more commonly found in a smaller form factor with 2 lines x 16 characters probably being the most common.

You will occasionally see displays like this with 4 lines but even they use a pair of HD44780 ICs with each separately addressed IC controlling 2 of the 4 lines.

The interface to the chip is parallel, but it can be configured to be 8-bit parallel or 4-bit parallel - 4 bit is slightly more complicated to use but it does mean that a single 8-bit port can be used to drive the 4 x data bits and two or three other control lines, and that's what I did for that display 'demo' in which the display is controlled by one of the 8154's two 8-bit ports.

The MK14 code sends the initial setup information to the display (to make it work in 4-bit mode) and then just sends that string of characters (in the form of ASCII codes) to the display. These displays are 'static' so you can send something to them to display and they will continue to display it indefinitely, or until the power is removed, so the display doesn't need to be 'maintained' by the host system in the way that the MK14's 7-segment display does.

[Roninfourseven]

OK, so progress!!! It's all wired up and I get a flashing LED when I run the save routine from 0052

I also see the correct signal on Pin 30 of the edge connector, and it must be arriving at the board and be doing something in order for the LED to flash.

What it isn't doing is sending a signal to the cassette out socket, so I need to go over my soldering again to see what's what, but I'll take it, it's a start

[Roninfourseven]

OK, so I did a bit of figuring out and realised that I had the tape output and input labelled the wrong way around due to the way it's written in the document.

Pin 3 says 'Tape in' but what it really means is 'output from the MK14 to the tape deck input'.

This drove me a little mad for a moment, but after plugging in an earphone to what I now know to be the output to tape, I can hear data.

Boy is it quiet though, so I need to go and figure out if I've messed up any of the wiring for the output half of the interface, what you see on the left side of the schematic.

[Realtime]

Originally Posted by Roninfourseven

Boy is it quiet though, so I need to go and figure out if I've messed up any of the wiring for the output half of the interface, what you see on the left side of the schematic.

I think that low level signal is correct as it is designed to feed the mic input of a portable cassette recorder, needing typically a few mV pk-pk. If you intend to use a more modern cassette deck or pc with line inputs then you’ll want to change the voltage dividers at the output to give about 600mV pk-pk.