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Thread: 10.7v on 12v Rail!! Faulty 300W ATX PSU???

  1. #1
    Constant Bitrate ironic's Avatar
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    Unhappy 10.7v on 12v Rail!! Faulty 300W ATX PSU???

    As title says!

    My desktop psu gives out 10.7v thru the 12v rail.

    Does this mean its faulty??
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  2. #2
    FLAC evandude's Avatar
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    did you measure it with some load on it? Switching supplies often don't regulate properly without one. If you have a load on the 12v rail and it's only giving you 10.7v, unless you've got some crazy wiring problem or something then I would say it's probably got issues.
    But don't take it from me! here's a quote from a real, live newbie:
    Quote Originally Posted by Viscouse
    I am learning buttloads just by searching on this forum. I've learned 2 big things so far: 1-it's been done before, and 2-if it hasn't, there is a way to do it.
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  3. #3
    Constant Bitrate ironic's Avatar
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    Unhappy

    yeh

    i am powering the m2-atx from the 12v rail.

    all molex indicated the following:

    12v rail = 10.7v
    5v Rail = 5.02v

    i am thinking that i my problems with my m2atx is coz my 300w psu is only feeding 10.7v thru the 12v rail.

    altho surprisingly enough, the molexes from my m2 indicate 12.23v on the 12v rail.

    any idea?? im clueless!!
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    Maximum Bitrate psyrex's Avatar
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    Are you completely overpowering the 12v rail on the 300w PSU? if you're pulling more amps than it can give, the output voltage can drop.

    The M2 is giving out 12v on it's output because that's what it's designed to do.

    -psyrex
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  5. #5
    Raw Wave Rob Withey's Avatar
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    The 12v line can droop, or the entire power supply shut off if you don't load the 5v line. This has been discussed many times.

    The reason it does this is to prevent overvoltage on the other lines output by the power supply, which are supplied by the same transformer.

    Edit : Overvoltage may be tripping on other lines too - check out the 3.3v line for example.
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  6. #6
    Constant Bitrate ironic's Avatar
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    Unhappy

    when i power it up i always have a hdd or a dvd drive which need both 5v and 12v railings for power.

    so i discard the 5v theory.

    could it be that my atx psu shuts off completely because of overheaitng because its trying to feed 12v on the 12v rail and it can only reach 10 for a limited amount of time?

    after it shuts off completely, i cannot turn it on again imeditately. i have to wait a few minutes before i can turn on the atx psu again.

    what do u think guys>?
    MSI KM4M-V Mobo -- AMD Athlon XP-M 1900+ -- 512MB DDR RAM -- LinITX 7" Touchscreen -- Seagate 8.4GB HDD -- LG DVDRW -- Onboard Graphics Card -- Onboard 5.1 surround sound -- Bluetooth Dongle -- RoyalTek Saphire GPS -- M2-ATX psu

  7. #7
    Maximum Bitrate psyrex's Avatar
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    Quote Originally Posted by ironic
    when i power it up i always have a hdd or a dvd drive which need both 5v and 12v railings for power.

    so i discard the 5v theory.
    I actually never heard of this 5v theory, but anyways, you seem to be powering solely off of the M2. As in the HDD/DVD is getting it's 5v from the M2? If so, it doesn't disprove the 5v theory.

    -psyrex
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  8. #8
    Maximum Bitrate eCarô's Avatar
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    Quote Originally Posted by ironic
    when i power it up i always have a hdd or a dvd drive which need both 5v and 12v railings for power.
    What type of HDD or DVD drive are you using? I don't know of any that need both 5V and 12V to operate (just because the molex that you are plugging into it has both, does not mean the drive is using both).

    ATX spec says that the PSU does not need to deliver the full 12V current unless there is some minimum load on 5V rail (don't know the definition of "minimum load" off the top of my head though). I suspect the load that a 2.5" HDD, or a slim CD/DVD-ROM, is not enough to allow you to pull 15A from the 12V rail.

  9. #9
    Constant Bitrate ironic's Avatar
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    below is the 5v "theory"

    Quote Originally Posted by Rob Withey
    The 12v line can droop, or the entire power supply shut off if you don't load the 5v line. This has been discussed many times.

    The reason it does this is to prevent overvoltage on the other lines output by the power supply, which are supplied by the same transformer.
    ecartm, on my dvdrw there is a sticker that says:

    5v / 12v -- 1.5A / 2.0A

    So i guess that its telling me that it needs both the 12v rail and the 5v to power itself. so if this is true, im already loading the 5v line.can anyone corroborate this?

    in any case, the real problem is im powering my m2atx from a 12v rail from my 300x psu that only gives 10.7v when devices are connected.

    AS i said, after a minute or so, everything shuts off and i have to wait for a few minutes to restart my atx psu.

    How can i tell if the problem is the atx psu or my m2atx??

    I need to know, so i can return my m2 on time to my retailer, before the returning of goods date expires!

    :S
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  10. #10
    Maximum Bitrate eCarô's Avatar
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    Quote Originally Posted by ironic
    How can i tell if the problem is the atx psu or my m2atx??
    Borrow the battery out of your car, and connect the M2 directly to it.

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