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Thread: National Semiconductor SC/MP Introkit

  1. #1

    Question National Semiconductor SC/MP Introkit

    Hey all,

    I bought few days ago a National Semiconductor SC/MP Introkit.
    It's currently not working.

    Here is some photos from the Introkit: https://imgur.com/a/cwheWbk

    I have three question about this computer.
    1. Has someone a manual for this computer? (I found on the Internet some manuals, but it is did not match with my Introkit.)
    2. What could be the other components?
    3. Anyone knows how much it is worth these days?

    Any info is much appreciated.
    (I apologize for my English, this is not my native language.)

    Thanks!

  2. #2

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    I can't help you directly but I think this video features a walkthrough repair of a National Semiconductor SC/MP Introkit. Maybe you could get into touch with the author of the video? I notice your PCB is not the same, it looks like a later more refined version.

    https://www.youtube.com/watch?v=fK-IZuIonnY

    There was a slightly later British derivative of the Introkit called the 'Science Of Cambridge MK14 Microcomputer'. Although it looks quite different it is electronically so similar that it was able to run the same 'Kitbug' operating system and had the same 20-key keypad as the Introkit with the same command keys 'Go / Mem / Abort / Term', so the method of entering code and running it will almost certainly be the same as it is described in the 'Version 1' MK14 manual.

    http://www.8bity.cz/files/MK14/mk14ManualV1_OCR.pdf

    The MK14 has an integral keypad and onboard display, and the Kitbug operating system is held in two 4-bit PROMs on the MK14 rather than one 8-bit PROM as it is on the Introkit, and the MK14 has onboard provision for an optional RAM-I/O device but there are many similarities otherwise.

    With regard to the worth of the Introkit I can only advise, as always, that you check closed / sold examples of the same system on ebay for actual historic selling prices.

    You say the system is 'not working', what are the symptoms?

  3. #3
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    Nice find...

    It certainly is a National Semiconductor SC/MP Introkit (it says so!) but the PCB layout doesn't look like anything I have seen before. It is the SC/MP 500D - so one of the multi-rail devices (as opposed to the SC/MP II 600D that is a single +5V rail).

    The wire-wrap stuff has been added by the original owner - and is non standard. It looks like some additional memory (2112 SRAM chips) but there is some other logic on there that doesn't look like anything to do with the expansion memory - but is most likely associated with the keypad interface (that was an add-on).

    Despite the fact that the PCB layout is different to a 'standard' NS Introkit - it shouldn't take too much time to work out what is and isn't working.

    What are you powering it from?

    How much test equipment do you have (e.g. nothing, a multimeter, a logic probe, an oscilloscope etc.).

    As to the other bits - who knows!? I can see a serial port there (the chip marked 8251) and some RS232 buffers.

    Price - it all depends on multiple factors... The biggest one being whether it is working or not!

    Dave

  4. #4
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    Looking at your last photograph - it looks like the three terminals of the voltage regulator have been shorted together on the underside of the PCB. I can't, therefore, see how this unit can work.

    If you have already connected a power supply, how did you connect it?

    Beware randomly connecting power to an unknown board - you can do the board damage...

    It looks like 0V and +5V are required.

    Also, -12V which is regulated down to a lower voltage by the three-terminal voltage regulator (the one that I think is shorted out). A 7906 is a -6V regulator.

    Dave
    Last edited by daver2; August 29th, 2019 at 08:27 AM.

  5. #5

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    Thank you for your answers.

    Quote Originally Posted by SiriusHardware View Post
    Maybe you could get into touch with the author of the video?
    I wrote a letter for him (and many other people). Currently I am waiting for the response.

    Quote Originally Posted by SiriusHardware View Post
    that you check closed / sold examples of the same system on ebay for actual historic selling prices.
    I searched on the Ebay (Completed Items / Sold Items), but I don't find anything about it.

    Quote Originally Posted by SiriusHardware View Post
    You say the system is 'not working', what are the symptoms?
    Quote Originally Posted by daver2 View Post
    What are you powering it from?
    Quote Originally Posted by daver2 View Post
    If you have already connected a power supply, how did you connect it?
    I'd correct my previous post: I haven't tested yet, because some pieces are missing (e.g. crystal), and I don't know what is the correct voltages for the board.
    I want to do more research before I do anything.

    Quote Originally Posted by daver2 View Post
    but the PCB layout doesn't look like anything I have seen before
    I found the same computer in this blog post: https://rainboworder.co.uk/2015/10/0...letchley-park/
    (Here is a larger photo: https://rainbowordertravel.files.wor...624371_hdr.jpg)

    Quote Originally Posted by daver2 View Post
    How much test equipment do you have (e.g. nothing, a multimeter, a logic probe, an oscilloscope etc.).
    Currently I only have a multimeter.

    Quote Originally Posted by daver2 View Post
    As to the other bits - who knows!?
    This is what I want to know.
    I think this is the most interesting board: https://imgur.com/1gHq5tG (SC/MP Application card)

  6. #6
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    It looks like the edge connector of the NS introkit is only used for power (0V, +5V and -12V). All of the other pins (from what I can see) are not connected to anything. This means that this card is pretty much stand-alone as far as I can see.

    The other cards are (presumably) part of something else that the previous guy was building. I suspect that some of the cards plugged into the 3-way backplane I can see. As for the rest???

    Quite happy to help you with the NS card - but anything else is going to be difficult.

    Can you let me know what test equipment (if any) you have and whether you have any electronic experience at all.

    Dave

  7. #7

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    In the video I linked to in #2 the main cause of the system being non-operational was failure of the KITBUG PROM, which the originator of the video fixed by grafting in an EPROM replacement. This system appears to have the same type of PROM, unsurprisingly.

    I'm not sure which memory technology the original PROMs used, if they were fusible-link then they do have an anecdotal tendency to develop internal 'tin whiskers' similar to those which affect old germanium transistors in metal cans. If the KITBUG PROM is a masked ROM then I'm not sure what the likely failure mode would be.

    In order to make some headway, more information is needed regarding fault symptoms - the OP is a new forum user, though, so his posts will be moderated for a while.

  8. #8
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    I certainly can't find any pictures of that type of PCB from NS.

    Looks like the crystal has been replaced with a capacitor?

    The other interesting thing is no 20 pin octal tri-state buffer - but an unused 16 pin IC instead. Two of these pins of the unused IC have been wire-wrapped into the 'birds nest' so it seems to me that the wire-wrapped area was designed in from the start by someone who knew what they were doing rather than an (extensive) modification to a standard Introkit.

    I may print out the front and back photographs of the card when I get back home and see if I can make sense of the 'glue logic'.

    Yes, posts being moderated. Been in touch via PM.

    Dave

  9. #9

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    It would be good if you could bring this into the open forum when you make some headway - there's not much 'chat' about these and even less about this somewhat unusual version.

  10. #10
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    We only talked about where he was based - and they have updated their profile.

    Good spot on the web of a photograph of a similar unit at TMoC! I might be able to get some information from them.

    I think your board has a crystal (although it may not be the same footprint as the big metal one you see in the one at Bletchley (unless someone has put a capacitor in place of a crystal).

    Also not sure why someone has put Green LED's in place of the capacitor either on the Bletchley PCB!

    We should be able to find out from the Bletchley unit what the device is that is not fitted to yours and what components are used for the keypad/7-segment LED interface. Whatever ICs are left are the extra RAM and whatever extra circuitry the original owner added.

    Good, please don't power the unit up until we are certain what we are dealing with...

    Dave
    Last edited by daver2; August 31st, 2019 at 08:56 AM.

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