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Thread: Northstar Advantage advice please.

  1. #31
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    Quote Originally Posted by daver2 View Post
    Nope.

    Close, but with something strange.

    Can you point me at the schematics?

    Dave
    Embedded in the back of the technical manual Dave - http://www.classiccmp.org/dunfield/miscpm/advtech.pdf

    Page 380 bottom right corner for the output connector to the CRT and I'm working back from there.

  2. #32
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    Cheers,

    I found the technical manual without the schematics first...

    Looks like the incoming mains frequency is used to feed a phase locked loop to provide the video dot clock.

    I then end up back at the VTIM ROM again.

    May be worth reading the text in the technical manual to see how this magic works!

    Dave

  3. #33
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    Quote Originally Posted by daver2 View Post
    Cheers,

    I found the technical manual without the schematics first...

    Looks like the incoming mains frequency is used to feed a phase locked loop to provide the video dot clock.

    I then end up back at the VTIM ROM again.

    May be worth reading the text in the technical manual to see how this magic works!

    Dave
    Yes, I end up back there too - That PROM is key to providing the sync signals - unfortunately in the version of manual I have the second half of sheet 2 of the main circuit board schematic is missing......

  4. #34
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    Plot thickens.....

    I better version of the manual and schematics is on bitsavers here: http://www.bitsavers.org/pdf/northst...anual_1981.pdf

    Interestingly the diagram indicates that the PLL circuit on European models was 'replaced with an oscillator'

  5. #35
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    This project has got its own legs now hasn't it?!

    I feel some veroboard coming on...

    Dave

  6. #36
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    Quote Originally Posted by daver2 View Post
    This project has got its own legs now hasn't it?!

    I feel some veroboard coming on...

    Dave
    Indeed.

    Of course I need to understand what the replacement oscillator actually has to generate from the PL Sync signals than emanate from the PROM but first I need to get that PROM replaced with a frequency correct version.


    .......Or I just buy a 60Hz pure sine wave inverter from the USA and feed from a suitable 12v supply........
    Last edited by zippysticks; September 21st, 2019 at 01:52 PM.

  7. #37
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    Last edited by ldkraemer; September 21st, 2019 at 03:22 PM.

  8. #38
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    Thanks Larry - yes thats really expensive. Some of those equivalents you listed seem a little cheaper. I don't currently have a way to program them though - my GQ4x doesn't support them.

  9. #39

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    You might be able to use an adapter like this one:


    PROM adapter.jpg


    It allows a normal EPROM to be used instead of the PROM. So if all else fails we can have a go at designing one for the 63S141. I actually had some of these tiny boards made up, so we should check the pinout of the 63S141 vs. the 82S123. If they match you may be in business.

    [Edit: They appear to be different. According to this document, 63S141 is 256*4 bits whereas 82S123 is 64*8 bits. But we can still design an adapter.]
    Last edited by JonB; September 22nd, 2019 at 12:14 AM.

  10. #40

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    I’ve used “Hobby ROMs” in the past for TTL PROMs and for programming. They were great to work with. They even programmed and mailed me another set of parts for free after I sent wrong data for the first try.

    They have the part you need for $12.00 and can program it as well.

    http://www.hobbyroms.com/proms.html

    Mike

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