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Thread: Nascom

  1. #41
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    LK1 is set to Int
    LK2 is jumpered
    LK3 is unjumpered
    LK4 has a removable jumper attached to one pin but nothing else.
    LK5 is jumpered to EXT
    LK6 appears to have no connections to anything.

    I see no evidence anything was attached to pin 10 of ic7 and it is in socket properly.

  2. #42
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    LK1 to INTERNAL means that the N1 performs its own I/O block decode and you can't add any I/O devices onto NASBUS. That's OK for the moment (especially if we want to run the N1 on its own).

    LK2 jumpered just specifies the number of stop bits for the UART. I can't get excited about this for now!

    LK3 unjumpered. This is a bit of a mystery as this link specifies where the input (RX) data comes from for the UART. If you chase IC26 pin 20 (the UART) does this go to a wire I wonder?

    LK4 is the UART clock for TX and RX operations...

    LK5 jumpered to EXT. This link will need to be changed to INT if we need to run the N1 on its own. You don't actually need to do any soldering as such - just jumpering this link to 0V will suffice. This link decodes for the 4K memory block where the N1 memory devices (debug monitor, video and workspace RAM) appears (i.e. 0x0XXX).

    LK6 - no connections. This is surprising as this link block selects the processor clock speed? The plot thickens!

    Dave

  3. #43
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    Thanks Dave.

    I feel like I'm in a bit of a bind with this one. Usually my preference is to go to ground and get down to bare bones functionality. But given all the modifications, including the keyboard, etc.. I wonder if there's any harm in wiring things back up where the connections are obvious, swapping out the PSU (the caps are leaking on this one, so that's another project even if I find a 110v transformer for it), and fire it up and see what I have? Even if I return the N1 to stock I still have to contend with the modified keyboard. On the other hand, figuring out all the mods might be impossible.
    Last edited by falter; November 19th, 2017 at 10:06 AM.

  4. #44
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    Returning to 'stock' would be a solution. Ideally, you want to do a full PCB check for cut tracks as these are the things that will catch you out.

    I don't know what the modifications are for the keyboard. They look overly complicated! As I remember the N1 to N2 keyboard modification it was quite simple (providing you could get hold of spare keys - which we did). The schematics are available online for the N1 keyboard; so returning it to 'stock' shouldn't be that difficult.

    Dave

  5. #45
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    Agreed. Okay, I've taken lots of pictures.. I think what I'm going to do is get down a step.. remove the Nasbus and all that from the equation.. and just get power and video hooked up, see what shows up onscreen.

  6. #46
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    Drat.. was ready to use my MMD1 PSU to fire up but forgot it doesn't put out -5V. Always something!

  7. #47
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    So I have two power supplies here.. neither has all the voltages I need but between them I do. I know this was done in the past with other vintage machines. I'm going to run the +5v, +12v and 0V off one of them, and -12V on the other. My question is, do I need to have ground going from the Nascom's ground pin to both PSUs?

  8. #48
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    NM.. I just reread the manual. Only need -12V for RS232. I'll leave that out for now.

  9. #49
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    Wired everything up to the defaults, removed the adapter in IC11 and put the 74LS11 on its own there. Removed all the add on wires, wired up to psu (minus the -12v lead) and powered up. All I get is a brief flash on screen. No characters, etc.

  10. #50
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    Ok so made a few discoveries. The 74ls123 at IC18 (think that was it..) had a pin bent out. There is a 74LS162 IC one up from it.. according to the manual that is supposed to be a 74LS163. Don't know what the differences are, but it looks like the tracks to that socket have been altered. Anyway, bending back the 123s pin now gives me a bit more signal onscreen. Nothing useful yet. I'm hoping I wired that right.. I did the center pin to p2 and the outside to ground?

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