UK Vintage Radio Repair and Restoration Discussion Forum

UK Vintage Radio Repair and Restoration Discussion Forum (https://www.vintage-radio.net/forum/index.php)
-   Vintage Computers (https://www.vintage-radio.net/forum/forumdisplay.php?f=16)
-   -   MK14 schematic revisions (https://www.vintage-radio.net/forum/showthread.php?t=145663)

SiriusHardware 3rd Jun 2020 12:28 am

Re: MK14 schematic revisions
 
One more thing, I recall that Phil down in France made himself a 3D printed frame to go over the top of his 'Martin' overlay to replicate the appearance of the anodised aluminium frame used on original MK14s.

If Phil is going to be sending a package over anyway perhaps he would be kind enough to include one of those frames, as that would be a good reference template for the hole positions and key positions.

TonyDuell 3rd Jun 2020 3:42 pm

Re: MK14 schematic revisions
 
I should still have the original SoC metal frame that I took off my MK14 to fit the Maplin keyswitches.

If I can find it I would be happy to make any measurements you need from it.

SiriusHardware 4th Jun 2020 6:49 pm

Re: MK14 schematic revisions
 
Tony, thanks for that offer, we'll see if Slothie would like to take that up at some point. There could be no better reference than one of the original keypad frames.

A couple of updates regarding the current version (revision 1.2) of Slothie's issue VI PCB - a few posts ago I said mine wasn't starting too reliably after I had fitted a (known working) 8154 RAM/IO IC, however I have now fitted a decent snug-fitting power socket and taken the value of the supply input capacitor down from 4700uF to just 470uF. After these changes the machine is back to coming up with the proper '0000 00' prompt every single time I power it up. In my case, the 14 positions for decoupling capacitors are still fully populated with 0.1uF parts.

Regarding Tim's alarming statement that he appears to have around 7V on some of the pins of the 8154 when the VDU is connected, I have just run through the default / after reset voltages on all of the pins on the edge connector on mine and I see nothing exceeding 5V. There is regulated +5V coming out on my 'VCC' connection on the underside of the PCB, as there should be.

The only ways I can imagine having 7V on the VDU are:-

-VDU being powered from 8V through separate regulator, which has lost its GND connection or is faulty. As far as I know Tim is just powering it from the MK14.

-It may be that the whole MK14 is running on 7V due to some problem with the main regulator. I really hope not.

It's worth pointing out that the LM340 is a 'family' of regulators which are available in a range of fixed voltages just like the 78xx series - they always have the 'LM340' part number but that part number alone does not signify a 5V regulator, there are further markings on the device to say which fixed voltage it actually is. That's why I generally stick with the 78xx series, the voltage is part of the 'big' main IC number.

The regulator in my PCB is an ST-branded 7805CV - the PSU I'm using as input is an old Uniross 'Uni 1200R' which is a 1.2A regulated multi-voltage linear supply. Originally I had the MK14 running on 9V from this supply and the heatsink was getting uncomfortably warm so I tried dropping to the 7.5V output (which is actually 7.6V off load) and to my surprise the output from the regulator is still 5.06V. I've had it running for a while now and it seems no worse than fairly warm.

Slothie 4th Jun 2020 7:15 pm

Re: MK14 schematic revisions
 
The 78xx devices have a dropout of 2v so a 7805 should be good down to 7v. I was going to solder a couple of 5A diodes in series to drop the voltage off my 9v power supplyto about 7.5v .

SiriusHardware 4th Jun 2020 9:03 pm

Re: MK14 schematic revisions
 
1 Attachment(s)
Probably worth doing, the drop has made quite a difference to the running temperature of my regulator.

Another snippet in respect of your replica PCB, I've attached a sketch of the edge connector connections looking at it from edge-on.

Timbucus 5th Jun 2020 12:23 am

Re: MK14 schematic revisions
 
Fitted a 100uF cap to the Composite out on the VDU card as I noticed a tingling touching the video lead (always noticed the same with the PSU as well) - video still works fine and thought I had beaten the funny voltages....

Refitted the 8154 and they were gone, then they came back...

Well I spent quite a bit of time before my virtual people / real beers Thursday evening, de-soldering (well destroying with a rework heater and extracting each pin) my nice red socket as I thought I had an intermittent ground connection for the 8154 which could explain the odd 7v on SIN and SENSEB if a chip was being powered through unusual pins - and flexing the 8154 seemed to reduce it to 5v - got a similar effect with my eliminator board.

Wow was that hard to get out thought I had cleaned the holes and decided to put a nice turned pin - got that trapped half way in as some holes were not quite clear and had to break it to take it back out - now fitted a standard socket and the fault is back but flexing the chip in that area has the same effect. So I thought.

Use the scope to look at the lines - nothing - meter also shows normal things - hmmm - difference my scope has a good ground... chasing ghosts again... ??? Thinking about it flexing the chip near there I could have touched pin 20 (GND)

I can only think it is to do with ground as if I touch the shield on the Composite the voltages drop the same way.... This is analogue stuff, like TV, radios and things.... not my wheelhouse....

Anyway as with my SCRUMPI - hook the ground clip from the scope to the board and all is normal... except I have lost my nice red socket and burned my fingers...

Timbucus 5th Jun 2020 12:23 am

Re: MK14 schematic revisions
 
By the way to calm nerves it is a rock stead 5.04 volts from the regulator....

SiriusHardware 5th Jun 2020 12:43 am

Re: MK14 schematic revisions
 
Your 'tingling' is due to the fact that you are using a un-earthed switched-mode supply. Try this:

-Plug the mains PSU into the mains
-Don't plug the DC power plug into anything
-Set your meter on AC Volts, select manual 200VAC range if possible
-Measure the AC voltage between the outer contact of the DC plug and any known good mains earth, such as one of the metal screw heads on a mains socket.

What voltage do you see? I'm guessing ...~115VAC. That's why you feel a tingle when you touch the 0V areas, such as the modulator casing, on your project.

The 115VAC is coming through a high voltage, low value capacitor which connects the low voltage side of the power supply to the high voltage side in PSUs like this. When you connect the scope 0V to the project, you are earthing that low current AC through the scope's mains earth so that's why the problem disappears when you connect the scope.

Now you see why I never use anything but linear supplies with sensitive old stuff like this.

If you have to use an SMPSU, select one which has a metal earth pin and has the 0V side of the DC output connected to earth. Better still, find or make a linear regulated supply to power these projects.

Timbucus 5th Jun 2020 12:50 am

Re: MK14 schematic revisions
 
Hmm funny on 200V AC only 0.6 to both my scope earth and the screw on the socket - I am assuming they are the same potential anyway as I use it as a good earth.

SiriusHardware 5th Jun 2020 12:53 am

Re: MK14 schematic revisions
 
Now I'm really baffled. ??? You had the PSU only, plugged in, mains turned on, and no AC voltage difference between the DC output and mains earth?

Timbucus 5th Jun 2020 12:55 am

Re: MK14 schematic revisions
 
29v on the composite shield... which would explain the tingling and why my 100uF CAP is doing nothing....

Timbucus 5th Jun 2020 12:56 am

Re: MK14 schematic revisions
 
...except protecting the TV from the 7v that is not there....

Timbucus 5th Jun 2020 12:56 am

Re: MK14 schematic revisions
 
... and maybe giving the effect you were seeking...

SiriusHardware 5th Jun 2020 12:59 am

Re: MK14 schematic revisions
 
If so, can you try the same thing with the TV / display, disconnect it from everything else, power it on, measure the AC voltage between the outer ring of the aerial socket and a known mains earth?

SiriusHardware 5th Jun 2020 1:01 am

Re: MK14 schematic revisions
 
Ah, cross posted - yes, there was a possibility that your unwanted 'tingle' source was the TV / display rather than the PSU.

Timbucus 5th Jun 2020 1:03 am

Re: MK14 schematic revisions
 
At least we will sleep better tonight...

SiriusHardware 5th Jun 2020 1:16 am

Re: MK14 schematic revisions
 
Yes, may be worth looking in the mains plug of that TV (if the plug is not a moulded type) and just making sure the earth screw, if the TV is earthed, has not come loose. I used to be the official PAT tester among other duties at our place and it was amazing how often the earth screws in fitted mains plugs (as opposed to moulded plugs) were found rattling loose. If the live or neutral came loose, that stopped the appliance from working and it would normally get looked at and sorted out, but a loose earth didn't cause any obvious problem and wasn't normally noticed until we came along.

Timbucus 5th Jun 2020 1:37 am

Re: MK14 schematic revisions
 
Will do - in the morning now, as it is into an 8 way extension behind this big desk for all the screens and table lamp but, I did just check the earth in the plug that the extension lead is running from - that could be really bad... it was fine.

I just realised that the scope is on that extension as well so that was a pointless test....

philoupat83 5th Jun 2020 10:27 pm

Re: MK14 schematic revisions
 
1 Attachment(s)
hello
a scan of the mk14 martin stick I scanned.
Iíll print you one of the facades I made for mine.

Slothie 5th Jun 2020 10:50 pm

Re: MK14 schematic revisions
 
1 Attachment(s)
That's a great scan! Could you measure as accurately as possible the following measurements A - F:

Slothie 5th Jun 2020 10:53 pm

Re: MK14 schematic revisions
 
Oh and the overall height/width and hole diameter for completeness. (G,H,I ?!)

SiriusHardware 6th Jun 2020 9:05 am

Re: MK14 schematic revisions
 
When I dug out my INS8154 datasheet last night I found inside it the original MK14 pull-out component layout diagram which I think is actual size, so it shows not only the original positions of all the ICs but the keys as well. I'll see if I can scan it over the next few days, it may provide useful backup corroboration of the dimensions, along with the dimensions from Tony's original metal keypad frame.

Also - not sure if I read it correctly but I think Phil was offering to send one of his 3D printed frames across - I think he is going to be sending one or more of his Scrumpi 1 PCBs to Tim at some point in the near future.

TonyDuell 6th Jun 2020 9:34 am

Re: MK14 schematic revisions
 
I have found my original SoC metal keypad frame now. Would you like me to make the same measurements. I don't think I can get a micrometer in there (and anyway I don't have one large enough to do the entire frame), I assume a vernier caliper will be accurate enough.

I am not convinced it's anodised aluminium though. It feels too heavy for that. I will test with a magnet just to be sure.

Slothie 6th Jun 2020 9:50 am

Re: MK14 schematic revisions
 
Yes, it would be great to have those measurements on here for posterity. I'd like to get my board right dimension wise particularly around the keyboard given the accessories that are becoming available.

SiriusHardware 6th Jun 2020 10:00 am

Re: MK14 schematic revisions
 
I have not seem my original key frame for decades, so my 'memory' of it being aluminium is probably wrong. I'm sorry to say I am sure that I threw away most of the original keypad components shortly after I built the replacement keypad the machine has now, thinking "Well, I won't be needing those again".

To understand that mode of thought you would really have to have experienced the full horror of the original issue II keypad. There was no thought of ever going back.

Oddly though, I do still have the original large conductive rubber square which was the 'active' part of the keypad. Maybe I thought it would come in handy for something else.

I'm wondering if the most useful thing Tony could do would be just to photocopy the frame several times and send the copies to Slothie, at some time when Slothie is in a better position to be able to use such materials.

Slothie 6th Jun 2020 10:45 am

Re: MK14 schematic revisions
 
Were the letters and numbers printed directly onto the rubber sheet or were they on a different layer of their own? I remember seeing a diagram somewhere of the original assembly but can't recall exactly where. Also, did the keypad with dome switches have the rubber over the domes or something else? I have a vague memory of clear plastic buttons but that would require a frame to retain them so that must have been very different.

SiriusHardware 6th Jun 2020 10:49 am

Re: MK14 schematic revisions
 
Also thanks to Phil for his beautiful scan of the 'Martin' keypad overlay - I still don't have the keyswitches for my issue VI but I have been pondering on the best way to produce the key legends to put under the transparent key caps when I eventually have them.

I did consider the 'Ransom Note' method of randomly cutting out the required figures from magazine pages, but it might have taken a few months to collect the command key words. ;)

As it is, I can just scale that scan up or down, print it on white card and cut out the key legends all beautifully done in the original font.

Slothie, the key legends were printed in black on a sheet of their own. The versions with dome switches omitted the rubber sheet. There may have been an early dome switch version where the user pressed the domes through the key overlay sheet (as per Martin's current version) but the final SOC version used the same black metal frame to retain clear plastic buttons which pressed on the key overlay, which in turn pressed on the dome switches. All versions had a metal frame, but in the early versions the frame was just there to hold the key overlay in place on the PCB - it wasn't self-adhesive like Martin's is.

philoupat83 6th Jun 2020 10:51 am

Re: MK14 schematic revisions
 
1 Attachment(s)
see sticker of martin mk14

Timbucus 6th Jun 2020 11:00 am

Re: MK14 schematic revisions
 
I am seriously thinking (when I get my 3D printer fixed) of making a housing a bit like the one for the JMP I have to fit the Slothie 1.2 size holes and keys with a version of that printed to fit under.

The feel on the JMP keyboard is quite good and it makes it look close the original. The Green key caps will eventually annoy me - I am looking for white ones at the moment!

SiriusHardware 6th Jun 2020 11:02 am

Re: MK14 schematic revisions
 
Thanks again Phil - that 'Martin' overlay actually represents two elements of the original keypad assembly. The key legends, 'Science of Cambridge' and 'MK14' were printed in black on a sheet of slippery, hard-wearing white plastic.

The heavy black outline framing the keys was not actually on the keypad overly sheet originally, it was an actual black metal frame laid over the top of the keypad overlay to hold it down flat on the PCB. That is the frame which Tony is talking about taking measurements from, and which Phil has 3D-printed a copy of.

philoupat83 6th Jun 2020 11:04 am

Re: MK14 schematic revisions
 
1 Attachment(s)
see stl of 3d printer

Timbucus 6th Jun 2020 11:06 am

Re: MK14 schematic revisions
 
Quote:

Originally Posted by SiriusHardware (Post 1256562)
Thanks again Phil - that 'Martin' overlay actually represents two elements of the original keypad assembly. The key legends, 'Science of Cambridge' and 'MK14' were printed in black on a sheet of slippery, hard-wearing white plastic.

The heavy black outline framing the keys was not actually on the keypad overly sheet originally, it was an actual black metal frame laid over the top of the keypad overlay to hold it down flat on the PCB. That is the frame which Tony is talking about taking measurements from, and which Phil has 3D-printed a copy of.

If you take a look at the photo of Mr Staff's one on the cz forum you can see he had some anodized metal ones made - there is a picture of the stack of them some way further back in the thread.

https://translate.google.co.uk/trans...78640%23p78640

Timbucus 6th Jun 2020 11:07 am

Re: MK14 schematic revisions
 
Quote:

Originally Posted by philoupat83 (Post 1256563)
see stl of 3d printer

Wow thanks - I really need to get my 3D printer working now.

Timbucus 6th Jun 2020 11:12 am

Re: MK14 schematic revisions
 
3 Attachment(s)
I am also kicking myself I missed getting a set of these that trev_ham listed on ebay... he did them for a while for the JMP and Martin boards

I have said elsewhere perhaps if contacted as a seller he might do them to order if people were interested.

Attachment 207794Attachment 207795Attachment 207796

philoupat83 6th Jun 2020 11:13 am

Re: MK14 schematic revisions
 
I also think mine need a great revision I made a hundred visiere for all my surroundings I am no longer of wire

philoupat83 6th Jun 2020 11:15 am

Re: MK14 schematic revisions
 
a yes very interesting

SiriusHardware 6th Jun 2020 11:16 am

Re: MK14 schematic revisions
 
Unfortunately I'm out, as even my original issue II MK14 would not accept those switches. If there is ever a rev 1.3 issue VI with the key positions remapped and re-pinned for those types of switches I would certainly go for it.

Timbucus 6th Jun 2020 11:26 am

Re: MK14 schematic revisions
 
Quote:

Originally Posted by philoupat83 (Post 1256569)
I also think mine need a great revision I made a hundred visiere for all my surroundings I am no longer of wire

Well done you for doing that - I was planning to try to help with something like that but, I have failed to get the Z axis to work reliably - its a mechanical issue I have just not spent enough time (and probably money) on.

Slothie 6th Jun 2020 11:28 am

Re: MK14 schematic revisions
 
Those look like standard D6 switches with custom keycaps. Later models of MK14 had provision for D6 switches didn't they?

Timbucus 6th Jun 2020 11:30 am

Re: MK14 schematic revisions
 
Quote:

Originally Posted by SiriusHardware (Post 1256572)
Unfortunately I'm out, as even my original issue II MK14 would not accept those switches. If there is ever a rev 1.3 issue VI with the key positions remapped and re-pinned for those types of switches I would certainly go for it.

Understood - it is not such an issue for me as I have the JMP version which works OK although it does not have the cutouts with the SOC and MK14 text on (I have a hand printed DYMO label on mine - very contemporary.

Now with Phil's STL once my printer is working I can add that to my Martin board to recreate the original feel to some extent - although a cold metal one is probably really needed.

If I get the printer working I will make an overlay for our VI boards in the fashion of the JMP one (I need a simple project for 3D design to learn) - if Phil doesn't buy more filament and do it first when he gets his Slothie VI...

Timbucus 6th Jun 2020 11:31 am

Re: MK14 schematic revisions
 
Quote:

Originally Posted by Slothie (Post 1256578)
Those look like standard D6 switches with custom keycaps. Later models of MK14 had provision for D6 switches didn't they?

Yes the Martin board is an exact copy of the Issue V so can have domes or those switches. I have gone for domes as I want a close replica.

SiriusHardware 6th Jun 2020 11:36 am

Re: MK14 schematic revisions
 
Quote:

Originally Posted by Slothie (Post 1256578)
Those look like standard D6 switches with custom keycaps. Later models of MK14 had provision for D6 switches didn't they?

Indeed they did. I have a full set of D6 switches in appropriate groups of colours (images earlier in the thread) but no holes for them to go into. :) Holes for 'proper' switches on original SOC PCBs didn't appear until issue IV onwards.

Slothie 6th Jun 2020 12:15 pm

Re: MK14 schematic revisions
 
I think there will be an issue 1.3 of my board sometime in the future (but don't hold your breath waiting!) Because I want to correct the dimensions and position of holes, find a keypad solution that works (or at least allow the JM one to be fitted), bring NENOUT to the edge connector, correct the silkscreen etc. Providing support for a multi page extension.looks tricky without adding more chips or completely redesigning the address decoding to use 74138 type chips. An alternative is to make a piggy-back board that sits on top that's connected by wires and includes the extra circuitry in a manner an enthusiast would have in the 80s. I'm warming to that idea considering multi page is an option that would appeal to relatively few people.

philoupat83 6th Jun 2020 12:17 pm

Re: MK14 schematic revisions
 
yes I have so many projects in progress I think youíll get there before me
:thumbsup::wall:;D

Timbucus 6th Jun 2020 1:03 pm

Re: MK14 schematic revisions
 
Quote:

Originally Posted by Slothie (Post 1256601)
I think there will be an issue 1.3 of my board sometime in the future (but don't hold your breath waiting!) Because I want to correct the dimensions and position of holes, find a keypad solution that works (or at least allow the JM one to be fitted), bring NENOUT to the edge connector, correct the silkscreen etc. Providing support for a multi page extension.looks tricky without adding more chips or completely redesigning the address decoding to use 74138 type chips. An alternative is to make a piggy-back board that sits on top that's connected by wires and includes the extra circuitry in a manner an enthusiast would have in the 80s. I'm warming to that idea considering multi page is an option that would appeal to relatively few people.

I think the Multipage would involve removing chips from the board and leaving the sockets empty - after all that is what we would have done as well BITD so don't dismiss that option. I was thinking the RAM board could have space for an 8K EPROM (NIBL and SCIOS would easily fit) as you can still get them cheaply and easily and the modern TL866I+ can program the 12v versions at least... BASIC /RAM board is an all in one then...

It feels fairly retro for an early 80's addon... as the bigger static RAMS were becoming available etc.

Timbucus 6th Jun 2020 1:33 pm

Re: MK14 schematic revisions
 
2 Attachment(s)
The design likely given by SoC (as there is a comment somewhere I can't remember - write for details) for the 1.5K by the way was:-

Attachment 207798

(from the Williamson and Dale "Understanding Microprocessors with the Mk14")

The article in PCW April 1980 (Called Beefing up the MK.14) creates an offboard paged RAM system by using a 40Pin header and moving the SC/MP to the expansion board... effectively buffering the base unit onto Page 0... and accessing the board using some of the address holes - that was the way I was thinking of going for my NIBL addon. It would work with any of my MK14's then. I cannot post the article as I have a copyright reprint from the Museum. - here is a snippet which probably counts under fair use...

Attachment 207799

Slothie 6th Jun 2020 1:36 pm

Re: MK14 schematic revisions
 
The obvious way to do it is to make a board that has the SC/MP on and plugs into the processor socket, allowing any signals to be intercepted with only a few wires required to connect to the edge connector for the extra address lines. The Elektor computer puts the 4k NIBL EPROM on page 1 so I could include a ROM on page 1, and 32k RAM socket and RS232 driver for a complete solution with minimal board modifications. It would also have the advantage of working on any MK14 and many other SCMP based machines.

Slothie 6th Jun 2020 1:41 pm

Re: MK14 schematic revisions
 
Oh looks like we crossed posts!

Slothie 6th Jun 2020 2:04 pm

Re: MK14 schematic revisions
 
Reading the PCW article I can see why they remap to an address hole, because the MK14 doesn't always gate the device selects with NRDS/NWDS as they should, so selecting a non-existent address makes sense. Where that address is I'm not sure - presumably somewhere in the display or keyboard areas.

Timbucus 6th Jun 2020 2:48 pm

Re: MK14 schematic revisions
 
2 Attachment(s)
No they use a portion of the 1.5K hole created on the Issue 5 - they do discuss modifying the INS chip areas as well but, that leads to issues as some software uses the shadows for various reasons.

My view would be that you would either use the simple expansion memory we plug into the expansion board used to hook up the VDU, Tape Interface, Provide headers for the INS8054 etc OR you use the offboard NIBL >4K memory system and it uses the hole we have already created or can be created on older boards with the mods given by SoC:

Extra notes with Issue 4: Attachment 207811

Not sure where these are from but, it is for earlier boards: Attachment 207812

Don't forget that the BASIC module in development by SoC used the new bigger 40 key keyboard which plugged on the edge connector so I would look to develop that and modify the Elektor Page1 NIBL to use it for input (and the VDU for output) rather than needing to use the Serial I/O although no reason both could not be supported.


All times are GMT +1. The time now is 8:53 pm.

Powered by vBulletin®
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Copyright ©2002 - 2020, Paul Stenning.