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Thread: Science of Cambridge (Sinclair) MK14

  1. #21

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    Quote Originally Posted by Ancient programmer View Post
    Just dug out my MK14 from the loft. When the original keyboard gave up the ghost I built the circuit board into an old Calculator body (Olympia CPA 1200), wired the keyboard up to the MK14 external connector and extended the display leads to make the display visible in the calc body. Worked fine with much quicker keyboard entry.
    My very first replacement keypad for the MK14 was a Texet 880 calculator which I bought new for about 6 GBP from Woolworths, removed the works from and painstakingly rewired the keypad to match the MK14's 'quirky' keypad matrix. Like you, I extended the display wiring to put the display inside the Texet's display window. That fell apart quite quickly because the plastic hinges on the keys / buttons were a design weakness, so then I built the keypad my MK14 has now (as seen in the YouTube clip referenced in post #16 of this thread) and put the machine back into something more like its original single-board computer form.

    With regard to trying to fix yours, well, hopefully reseating the ICs has fixed it - but if not...

    If your external keyboard is connected to the MK14 via a plug-in edge connector, disconnect it and reset the machine. Does the display look normal now? (The keyboard edge connector doesn't have a 'key' to keep it in the correct place, relative to the contacts on the PCB. If the keyboard edge connector slips upwards or downwards from its correct position, it can end up joining one or more of the keypad / display lines together, stopping the keyboard from working and causing some odd looking effects on the display).

    If your board is fully populated with socketed ICs try 'minimising' the system by removing the optional 8154 RAM I/O chip and the two additional RAM chips to restore it to its original unexpanded condition. Does that make any difference to your fault?

    Yes, I've seen that one being offered (but noticeably not selling) for 1.5K GBP. There's also another one going for about a third of that but the keyboard in particular looks in very rough condition, either tobacco smoke stained or badly sun yellowed.
    Last edited by SiriusHardware; February 10th, 2015 at 02:47 PM.

  2. #22
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    Another MK14 surfaces! Welcome to the forum Ancient programmer...

    Yes, there is the 1,500 one (that in my opinion shouldn't sell at that price). I also noticed one at a starting price of 500 that never went. It has been re-listed at 100 and people are slowly bidding on it. I suspect the MK14 market is getting a little bit saturated now. One did go a while ago for about 650 ish (if I remember correctly).

    Yep - reseating the IC's would be the first port of call. Have a look at the IC pins for tarnish. If they are in sockets - and are tarnished - take the ICs out and clean the pins. I did have an interesting fault with an Apple iie disk controller card. The pins of the IC were tarnished - and when I took the ICs out of the sockets some of the pins got left behind! The 'tarnish' had actually 'eaten' right through some of the pins and they were actually floating.

    Do you have any test gear (e.g. an oscilloscope)?

    Does pressing any of the keys change the display at all?

    I remember writing some posts relating to fixing the display of someone else's MK14 on the forum somewhere. I can't just find it at the moment - but it was a while ago.

    You may find buying a simple logic probe from Maplin (FY73Q) will identify the problem quite quickly. By probing around the keyboard/display logic you may find a pin that is either stuck high or low or completely open circuit. Just a thought. I would be able to identify what pins for you to look at if that would help.

    If you are only up in Wolverhampton and fancied a trip to Worcester on a weekend I could get my 'scope on it for you.

    Dave

  3. #23

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    Just noticed a fairly new (Spring 2015) Youtube clip of a working Science Of Cambridge (Sinclair) MK14 in very nice condition: Quite hard to find it though, because if you type 'MK14' into Youtube you get inundated with results concerning some kind of assault weapon.

    Anyway, here it is...

    https://www.youtube.com/watch?v=aGt9E46gH14

  4. #24

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    Quote Originally Posted by daver2 View Post

    Yes, there is the 1,500 one (that in my opinion shouldn't sell at that price)... I suspect the MK14 market is getting a little bit saturated now. One did go a while ago for about 650 ish (if I remember correctly).

    Dave
    We first talked about that MK14 more than a year ago now... I've been keeping an eye on it ever since and there were always a lot of people watching it (probably wondering if anyone would really be mad enough to pay so much) - but I guess all the mad people with more money than sense must already have one by now.

    It didn't go even when the price eventually dropped to the sub-1000 mark.

    It has just (March 2016) been relisted again for the now drastically lower starting price of 400 and with carriage costs quoted - until now it was always collect-only, probably with a view to the age and fragility of the unit.

    400 is still a lot of money for what it really is - a very basic microprocessor development / training system. The seller goes as far as stating that it displays the correct '---- --' prompt but has not been tested further. (?).

  5. #25
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    Yes. I have been watching that one for a while myself.

    I agree, 400 is too much for what it is.

    I see now that two bidders are fighting over it - so it is going to get sold this time around. I am not one of them though...

    Dave

  6. #26

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    Hello Dave.
    Many thanks for your reply and offer of help.
    (I'd assumed that I would get an auto response if someone replied to my email, which is why I didn't log back in.)

    It's been a while since I tried to get it working and I can't remember what I did, so I'll have to dig it out and try again. I'll post again once I've had a go.
    Cheers
    Glenn
    P.S. Last year I went to Bletchley Park for the day - Enigma, Colossus etc, amazing stuff - and also to see the WHICH computer, which I programmed briefly as a student in the 1960's. Great to see it working again!

    Quote Originally Posted by daver2 View Post
    Another MK14 surfaces! Welcome to the forum Ancient programmer...

    Yes, there is the 1,500 one (that in my opinion shouldn't sell at that price). I also noticed one at a starting price of 500 that never went. It has been re-listed at 100 and people are slowly bidding on it. I suspect the MK14 market is getting a little bit saturated now. One did go a while ago for about 650 ish (if I remember correctly).

    Yep - reseating the IC's would be the first port of call. Have a look at the IC pins for tarnish. If they are in sockets - and are tarnished - take the ICs out and clean the pins. I did have an interesting fault with an Apple iie disk controller card. The pins of the IC were tarnished - and when I took the ICs out of the sockets some of the pins got left behind! The 'tarnish' had actually 'eaten' right through some of the pins and they were actually floating.

    Do you have any test gear (e.g. an oscilloscope)?

    Does pressing any of the keys change the display at all?

    I remember writing some posts relating to fixing the display of someone else's MK14 on the forum somewhere. I can't just find it at the moment - but it was a while ago.

    You may find buying a simple logic probe from Maplin (FY73Q) will identify the problem quite quickly. By probing around the keyboard/display logic you may find a pin that is either stuck high or low or completely open circuit. Just a thought. I would be able to identify what pins for you to look at if that would help.

    If you are only up in Wolverhampton and fancied a trip to Worcester on a weekend I could get my 'scope on it for you.

    Dave

  7. #27
    Join Date
    Jun 2003
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    Northwest (UK)
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    Quote Originally Posted by SiriusHardware View Post
    The seller goes as far as stating that it displays the correct '---- --' prompt but has not been tested further. (?).
    I'd guess it hasn't been tested further as it is faulty? Shouldn't it be displaying '0000 00' at power up? Still, it looks to be in pretty good condition and should be pretty simple to repair.

    I've actually been toying with the idea of building a reproduction MK14 board. There are no parts that are super hard to find so it should be a fairly simple machine to replicate and for a fraction of the price originals go for.

  8. #28

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    Quote Originally Posted by Moonferret View Post
    I'd guess it hasn't been tested further as it is faulty? Shouldn't it be displaying '0000 00' at power up? Still, it looks to be in pretty good condition and should be pretty simple to repair.

    I've actually been toying with the idea of building a reproduction MK14 board. There are no parts that are super hard to find so it should be a fairly simple machine to replicate and for a fraction of the price originals go for.
    Already been done, see this nice little Youtube timelapse video of a guy across in Greece building his entirely scratchbuilt reproduction issue II MK14. I exchanged a few emails with him and he did eventually get it working.

    https://www.youtube.com/watch?v=vhSAMRwGL-A

    The "---- --" prompt is correct for the original version of the monitor - the "0000 00" prompt came with the much improved 'new' monitor which was initially offered as an after-sales option and then eventually supplied as standard with later MK14s. My main concern, since that machine is carefully NOT described as 'working', is about the keypad. If the keypad is working it would only take a few keystrokes to type a short test program from the manual into the machine and run it. If you go all the way back to the start of this thread, it started because the OP had been sold an MK14 with the conductive rubber contact mat from the keypad missing. (I'm not suggesting this is the same machine - just pointing out that it happened at least once before).

    For a collector who just wants to own the machine, not really to use it, I would say the original monitor is the better one to have because it matches the operating instructions in the manual. For anyone wanting to play with it, though, the 'new' monitor with the "0000 00" prompt is far better for several reasons: It includes firmware to run the optional cassette tape interface (the original monitor did not), it includes firmware to run the optional 'single step' feature, but best of all it takes far fewer keystrokes to enter each byte of code into the machine.
    Last edited by SiriusHardware; March 31st, 2016 at 12:09 PM.

  9. #29

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    Quote Originally Posted by daver2 View Post

    ....it is going to get sold this time around. I am not one of them though...

    Dave
    Nor me, as I still have mine - battered, original keypad long gone, but working.

  10. #30
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    I noticed that the one on e-bay had it's description changed from the last listing. It originally said that when you pressed some keys the display changed. It looked like the picture had examined a memory location in the ROM. The listing was ended early by the seller 'due to a description error' and re-listed much cheaper - but the "when you press a key the display changes" has been removed. I suspect the keyboard now no longer works?

    It's a pity the guys that have already made an MK14 PCB are not sharing. I have all the components to make one - just missing the PCB.

    Welcome back ancient programmer. You only get an e-mail when someone sends you a private message - not when someone replies to a post. Until recently, new members couldn't send PM's and existing members couldn't send PM's to new members until they had reached a certain post limit. That restriction has now been lifted - so I thought I would send you a PM to see if you were still active with the MK14. Please try and get it working again - it would save yet another bit of British computing history from disappearing!

    It's interesting you mention WHICH - I am looking to do a long-term Javascript simulation of WHICH at the individual component level. How I am going to do it I don't know yet - but that's never stopped me from doing something before! Still in the planning stage for that one. I did a NOR gate-level implementation of the Apollo Guidance Computer from the MIT schematics a few years ago. That turned into a mammoth project - but I managed it in the end...

    Do you have any of your programs for WHICH lying around in the attic with your MK14?!

    Dave

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