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Thread: Northstar Advantage advice please.

  1. #21
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    Well, the Advatnage has turned up on my doorstep while I was out this morning.
    Amazingly its case is intact considering how poorly it had been packed (see photo) and the distance it has travelled from the USA.

    It powers up and after a few tries boots from the main drive - will try cleaning the drives anyway as it won't boot from the 2nd drive.

    The CRT retrace lines on display were easily fixed by turning down the brightness control but I have a different, more challenging problem with picture stability - see video link.

    What do you think - something loose, bad caps, solder joints ?

    IMG_20190921_094527110.jpg

    Last edited by zippysticks; September 21st, 2019 at 02:48 AM.

  2. #22
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    Nice acquisition.

    My first guess would be that you have some ac voltage where you shouldn't. My first thought would be a smoothing capacitor on a dc supply in the monitor is poorly and not doing its job right. You should be able to identify this with an oscilloscope on the dc supply rails. If you start poking around on high voltage supply lines, ensure you have the right tools and understand what you are doing.

    Dave

  3. #23
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    I might have found the problem - there are two vertical timing settings for 50hz and 60hz available on this machine - there is a prom that needs to be swapped at position B14 on the board if operating at 50Hz - need to swap VTIM for VTIM50.

    Its a 63s141n 256*4 bipolar PROM by all accounts.

    Bugger.

    The technical manual does table the contents of the proms - not sure if I can get some and program accordingly as it seems to be obsolete and so do all teh listed equivalents.

    Anyone have some ?
    Last edited by zippysticks; September 21st, 2019 at 04:49 AM.

  4. #24
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    Should be able to use these equivalents for the 63S141:

    256x4

    Fujitsu 7114TS
    SIG 82S129
    AMD 27S21
    MMI 6301, 63S141J
    NAT 74S287
    TI 24S10, 34S10
    HAR 7611
    FAR 93427

    REF:
    https://www.mikesarcade.com/cgi-bin/...ge=PromRef.txt


    Larry

  5. #25
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    Thanks Larry - not sure my programmer will actually support any of those devices.

    Anyone in the UK have a programmer that can write these 256*4 PROM devices ?

    I'm still not entirely sure that this is the only problem - would a 60Hz rather than 50Hz vertical sync frequency really cause this wobbling ? I could understand a little flicker under mains powered lighting. Having said this, in the Ebay listing photo the display looked steady on a US 60Hz supply.

    Thanks
    Last edited by zippysticks; September 21st, 2019 at 10:48 AM.

  6. #26
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    Been scoping the horizontal and vertical sync signals on the mainboard and there does seem to be quite a bit of jitter on both signals.

  7. #27
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    I'd persevere with that avenue for a while first.

    Dave

  8. #28
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    These don't look right do they....horizontal sync first


  9. #29
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    And then the vertical....


  10. #30
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    Nope.

    Close, but with something strange.

    Can you point me at the schematics?

    Dave

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