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Technical question about power supplies and spontaneous reboots

Discussion in 'Hardware' started by Alex Ethridge, Nov 22, 2009.

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  1. Alex Ethridge

    Alex Ethridge Thread Starter

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    Hypothetical situation:

    The givens:
    • desktop computer
    • a power supply with intermittent voltage drops
    • voltage occasionally drops enough to cause a spontaneous reboot.
    • voltage is being monitored on the 12-volt leg
    • wall current integrity is good at all times
    When a spontaneous reboot occurs, what voltage should one see this occur at?
     
  2. NICK G

    NICK G Banned

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    What difference would it make? Threshold voltages would not be constant with all computers.
    If your input power is stable but PSU outputs unstable, replace power supply.
    Good luck.:)
     
  3. Alex Ethridge

    Alex Ethridge Thread Starter

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    An unresponsive reply is a waste of both out times and pollutes the thread.
     
  4. socc4roos

    socc4roos

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    A little uptight there Alex?

    You're the one posting a 'hypothetical' question.
     
  5. Alex Ethridge

    Alex Ethridge Thread Starter

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    Yep, a pet peeve of mine. It happens here too often where a question is posed and so-called "contributions" come in that are irrelevant and only tangential to the subject.

    "I don't know", would have been equally useful--or useless, whichever way you want to look at it.
     
  6. win2kpro

    win2kpro

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    Alex, monitor the +5v rail. +5v controls the starting and stopping of the board. The voltages on +5v are 4.75v-5.25v.
     
  7. Alex Ethridge

    Alex Ethridge Thread Starter

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    Thanks,

    I have one here that restarts spontaneously. I have a meter that interfaces with the computer that also uses a program to record voltage every second to a text file along with the exact time down to the second. The voltage on the 12-volt side is never lower than 11.79. Years ago, I had one that didn't restart until it dropped to about 10 volts; but, it was in the days of Windows 3.1 or maybe Windows 95 and I have forgotten the exact voltage.

    I could just replace the power supply and see what happens; but, I'm trying to learn something here.
     
  8. win2kpro

    win2kpro

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    +5v for starting and stopping is the critical voltage rail. When the +5v rail "drops out" or "drops down" on the +5v rail the machine is going to shutdown or restart.

    We see this quite often with USB problems since it also operates on the +5v rail. When a USB device overloads this is when it shuts down the board just as if the power plug has been pulled. As you know in those cases, it is generally necessary to unplug the power supply from the source for 20-30 seconds so that the +5v rail can reset, and remove the offending USB device.
     
  9. Alex Ethridge

    Alex Ethridge Thread Starter

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    Thanks.

    I didn't think about the 5-volt USB being a factor; but, in this case, it does it whether we have any USB connected or not.

    I'm going to connect that monitoring system to the 5-volt and see what happens. After that, it'll be a replacement of the power supply.

    Again, this is a learning-through-experimentation project.
     
  10. win2kpro

    win2kpro

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    Today most everyone puts all the emphasis on the +12v rail power because of the high power requirements of PCIe video cards and high powered processors.

    +3.3v and +5v are still extremely important for computer operation, and although it varies from power supply to power supply you will still see that most power supply's will have roughly 40-60 amps combined on the +3.3v and +5v rails. Many times on lower power power supply's the +3.3v and +5v rails combined or singularly will provide more amps than the +12v rail.
     
  11. NICK G

    NICK G Banned

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    You pollute your own thread if you think a valid response from an Electrical Engineer and
    Computer Engineer is a waste of "out" times.:p I know I wasted my time with it.:rolleyes:
    You put out some stupid $h1t and then elaborate on it when you don't get an expected answer
    as you desire. I'm not a frig'n mind reader, twat.:cool: I should have guessed the theory of
    electricity would have been a better reply. NOT!:) Get over yourself already.
     
  12. Alex Ethridge

    Alex Ethridge Thread Starter

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    There are competents incompetents in all professions.
    No crystal ball needed for words clearly arranged so as to make a 'misunderstanding' highly unlikely. Seems like others had no problem with it. If you don't have a proper reply; refrain from posting irrelevant opinions.
    There are no 'theories of electricity' in there.
     
  13. NICK G

    NICK G Banned

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    Merely a hypothetical response to an obvious hypothetical rude dude.:p
    Did I mention this was all hypothetical?
    If I don't know if one knows a quark from an elephant I use the KISS method.
    Technically PSU regulated outputs are Accuracy For Voltage : 0.5 percent +/- 1 dgt
    For Current : 0.5 percent +/- 1 dgt
    Anything out of this range could cause spontaneous reactions on the load.
    But variables always cause this to either be true or false at different times for different components.:)

    Oh, sorry, as I just saw your location. Now I understand.
     
  14. Alex Ethridge

    Alex Ethridge Thread Starter

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    You sure are wasting a lot of energy polluting my thread. Do you realize how much control of your time you've given me?
     
  15. Alex Ethridge

    Alex Ethridge Thread Starter

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    Well, I guess this has now turned into something besides a power supply experiment.

    The power supply has nothing to do with this as I have replaced the power supply with a known-good supply and there are still these spontaneous restarts.

    So far, I've eliminated the memory, power supply, hard disks, optical drives, modem and DVR/TV card.

    All I can see that is left is the main board, the processor and the display controller.

    I guess that is the end of this thread.

    Thanks for the help.
     
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