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Thread: An IBM 5150 that won't IBM 5150

  1. #1
    Join Date
    Oct 2016
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    Illinois, USA
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    Default An IBM 5150 that won't IBM 5150

    So, I've picked up a IBM 5150 at VCF Midwest earlier -- 64-256k. It was tested and demonstrated to work prior to my acquisition of the system, and I got it from a trustworthy community member. I got home, did some light dusting and fired it up, but POST never kicked in. The PSU fan spins and stays spinning, and the 5153 goes from gray to black as if it's gonna display something...but it never does. The underscore that indicates testing is in progress never appears/ I never hear any beeps, good or bad, and the system just sort of never gets anywhere in general.

    DIP switches are correct for the diagnostic setup and there's nothing obviously awry with the motherboard. Per the MinusZeroDegrees guide I've ruled out a bad PSU and shorts on the system board, rails are all within spec voltage-wise and a PSU substitution didn't change anything. Next culprit's the RAM, but I've reseated everything I can and piggybacked everything I can to no avail. In addition, I've also reseated any and all socketed chips I could find.

    I imagine some Landmark ROMs would be illuminating, but I don't have 'em handy... what's my next step?

  2. #2

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    I would start probing with an oscilloscope to see that voltages look good (e.g. close enough and not too noisy), clock is being provided to the CPU, a correct RESET pulse occurs, address lines are changing, etc.

    Do you have a copy of the Intel iAPX 86, 88 User's Manual ?
    Last edited by Uniballer; September 16th, 2018 at 03:05 AM.

  3. #3
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    Oct 2016
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    Default

    Unfortunately, I don't have an oscilloscope - I did verify that the voltages were within spec using my multimeter, but that's about all I can do.

  4. #4
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    Quote Originally Posted by MrArgent View Post
    I imagine some Landmark ROMs would be illuminating, but I don't have 'em handy... what's my next step?
    "Get the Landmark ROMs" would be my suggestion.

  5. #5
    Join Date
    Oct 2016
    Location
    Illinois, USA
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    Default

    Aye. Gonna be getting in touch with a friend who'll likely be able to write me some once I have cash spare.

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