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Thread: XT clone crashes

  1. #1
    Join Date
    Aug 2018
    United States

    Default XT clone crashes

    So I found a PC XT clone on Craigslist, bought it, and after some initial cleanup and re-formatting the (still-working!) hard disk it seemed to work fine. However, as I started using it for longer times, I noticed it would always freeze up after some time. Always, it would stop working with no warning. The two failure states that are most common are thus:
    -screen freezes, computer accepts no input at all, save for the power switch.
    -screen freezes, the only input that does anything is ctrl-alt-del, which resets it as normal.
    However, on occasion it will give an error. I have encountered these so far:
    Parity NMI at XXXX:XXXX.
    Type (S)hut off NMI, (R)eboot, other keys to continue
    {however, no keys do anything. The two values I've seen for X are 0070:0911 and 0291:033A. Once, it happened immediately at startup, once after a couple minutes use}

    <incomplete RAM check (e.g. 381K) here>
    XX RAM bad XXXXX
    <same RAM check here>
    Error. Press F1 to continue.
    (this usually happens directly after rebooting the computer after a crash)

    FATAL: Internal Stack Failure
    Please Reset.
    (I've only seen this once)

    (note that any of these are quite rare compared to the normal no-feedback crash)
    The BIOS identifies itself as "Phoenix ROM Ver 2.51" and also prints out "Upjohn Pharmaceuticals" (presumably they contracted whoever to give them a bunch of computers, and they got to put their name in the BIOS as part of the deal). I've tried it with minimal cards (CGA, floppy, and hard drive only), reseated every RAM chip, and running it with no cover to check if it is a thermal issue. No dice. It fails at a seemingly random time, but I've never been able to go for more than 20 minutes without it crashing.
    I'm thinking it's the RAM, but I could easily be mistaken. I would think if there was a RAM chip bad it would fail the memory check every time, but it doesn't.
    Has anyone else had this or a similar issue? Can I fix it easily? Or should I just put this box in the "for parts" category and look for a proper IBM?

  2. #2


    Clean out each RAM socket and clean each RAM chip. Then try again. In case that is an issue you may be able to run targeted diagnostics (burn in). I know people troubleshoot 5150s when restoring those that way.


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