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Thread: PC 5150 Mysteriously Reboots

  1. #1

    Default PC 5150 Mysteriously Reboots

    On today's computers troubleshooting mysterious reboots seems a lot easier; bad device driver, usually video card or in some cases I've seen storage drivers or bad memory or power supply. However on my 5150 with expansion unit it either reboots randomly (so random and so infrequently I really cant tell whats up) even though I've run advanced diagnostics and just let it go (infinite loops) and it won't ever report a failure in CPU, RAM, FPU, etc...) however it might randomly reboot. Could it be bad ram or bad PSU?
    Daniel P. Cayea - The Lyon Mountain Company - Plattsburgh, New York 12901
    Vintage Equipment: IBM 5150 * IBM 5161 * ThinkPad 770ED
    Modern Equipment: MacBook Pro 13 * Alienware M15R3

  2. #2


    Quote Originally Posted by lyonadmiral View Post
    Could it be bad ram or bad PSU?
    Absolutely... just like it could be practically anything else as well. Good luck.
    PM me if you're looking for 3" or 5" floppy disks. EMail For everything else, Take Another Step

  3. #3
    Join Date
    Jan 2013
    Marietta, GA


    If it were me, I'd first try to find something that it is doing that makes it more likely to reboot. Diagnostics usually only test one thing at a time. Perhaps there is some program that chunks the I/O and keeps the CPU doing things. Perhaps some game or 8088 domination / 8088mph.

    Does it ever randomly freeze instead of reboot? Usually when some bit gets tripped up, a machine is more likely to freeze as the CPU tries to execute garbage.

    Does it reboot when you are not touching it? If not, it could just be some bad connection somewhere.

    The PSU is not a bad place to start. Even in "modern" machines I have seen parts act intermittently erratic until the PSU is replaced.

    Unfortunately the root cause could be a marginal component somewhere, even an IC, that could be difficult to narrow down.

  4. #4
    Join Date
    May 2006
    Melbourne, Australia


    One possible cause for a motherboard reboot is the POWER GOOD signal from the power supply (see [here]) going low then returning to high.

    Some things might trigger that:
    1. Unstable mains power (house power) into the power supply. (E.g. Air conditioner kicking in.)
    2. Faulty power supply.
    3. Something in the computer is from time to time temporarily overloading the power supply.

    Re point 3. That for example (repeat: example) could be a tantalum capacitor that is 'breaking down'.


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