Woops PSU Blown A7N8XD & Enermax PSU

Discussion in 'Asus' started by Bill H, Oct 22, 2005.

  1. Bill H

    Bill H Guest

    Hello;

    ASUS A7N8X Deluxe and Enermax 350W PSU.

    The missus switched on the PC and said that it immediately immited a loud
    bang.

    I checked it out and when the UPS is switched on it fails.

    Removed the UPS and connected straight into the PSU with a new connector,
    another bang!!

    Removed the PSU and took it apart no obvious burnt out components, change
    the fuse in the power connector and switched back on..........fireworks came
    early this year!!!

    I tried out a spare PSU that I had in the garage but the system case would
    not power up dead as a Dodo, problem is not sure the PSU was working anyway?
    Tried to test the PSU on its own from info off the web (Connect the green
    wire to any common and switch on) Nothing happened, so PSU might be duff.

    Well I now have a dilema, I know I need a PSU so I'll have to get one but
    what are the chances of the Mobo being fried??
    Tried an Ohm test on the power connectors on the HD's and CDRom and no
    obvious shorts but how can I test the Mobo (Again no obvious damage)

    If the Mobo is damaged what are the chances of a damage Mobo blowing a new
    PSU??

    Last note when I took the Enermax apart the internal fuse was intact?

    Any help would be great. Need a PSU in a hurry only shop open tommorow is PC
    World and think they only sell JeanTech.

    Regards

    Skavenger
     
    Bill H, Oct 22, 2005
    #1
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  2. Difficult to say, about the only thing you can do is try a known good PSU.
    Can try that, that's not likely to tell if it will actually work though.
    Unlikely, unless the PSU is so badly designed it should be thrown in the
    trash. If it's shorted it should just not power up.
    Possible things can blow without taking out the fuse..
     
    Robert Hancock, Oct 22, 2005
    #2
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  3. Bill H

    Paul Guest

    There is a big difference between "no obvious shorts" and "it works".
    Testing for shorts on the motherboard doesn't tell you whether it
    will work when powered the next time or not. Internal damage to
    silicon, does not mean you can necessarily see the effect externally,
    as measured by an ohmmeter.

    To test the motherboard, measure from +3.3V to COM, from +5V to COM,
    from +12V to COM, from +3.3V to +5V, and so on. In other words, test
    for rail to rail shorts, test for rail to ground shorts. There are
    multiple +3.3V and +5V wires, but you don't need to test all
    combinations of the wires, just obvious combinations of +3.3V, +5V,
    +12V, -5V, -12V, +5VSB, and COM. Since there could be filter capacitors
    on some of those rails, some of them could give a steadily increasing
    reading, which is fine.

    When a PSU makes a loud "bang" sound, that is the last time you
    plug it to a motherboard! Even if you were to send it to a shop
    and have it repaired (which would not be cost effective), I would
    never trust $1000 worth of electronics to a suspect $39 box full of
    destructive power.

    The purpose of an internal fuse inside a power supply, is mainly
    to protect the wiring in your house. The fuse cannot possibly work
    fast enough, to prevent damage to the load side of the PSU. It is
    more of a fire prevention feature than anything else.

    Your A7N8X draws most current from the +5V rail. Depending on whether
    you have a high power video card or not, I would want a new power
    supply with 5V @ 20A rating (for a video card that doesn't use a
    disk drive power connector) to 5V @ 25A (for a video card that does
    use a disk drive power connector for extra power). The other rails
    are not as critical. This is different advice than I would give for
    the current generation of motherboards, where the majority of power
    comes from +12V (in which case 12V @ 15A would be a bare minimum, and
    certainly a bit more than that would not hurt).

    Check the label on the side of the Jeantech, to see if it at least
    meets the +5V requirement of your current motherboard, but also
    make sure it has a good +12V rating, if you plan to use it for a
    future motherboard.

    Paul
     
    Paul, Oct 22, 2005
    #3
  4. Bill H

    Skavenger Guest

    Thanks for all the help,
    As I needed to fix it today after carrying out some more tests, Ohm Test on
    Mobo Power Socket, I popped down to PC World this morning (Only place open
    on a Sunday).

    PC World only sell Jantech and one Hipper (£69.99) I had already checked the
    specs on the Net, needed a 450W to be sure but low and behold they only had
    the Jeantech 400W (£39.99) & 600W (£69.99).
    After a bit of a discussion with the promise of it it don't work or blows up
    cos you have a faulty Mobo bring it back and we'll refund you I took it the
    Jeantech 400W JNP-400P.

    The power rating seemed OK, but having two +12v ratings confused me
    slightly.

    +5V 35A
    +3.3V 28A
    +12V1 15A
    +12V2 17A

    What are the two +12V.

    Took it home connected it all up and voila my Neon Fan kicked in and the
    machine started up and is working fine, tested it running Unreal Tournement
    and all seemed OK.
    Two zaps with a busted PSU and the Mobo survived.......phew
    The Jeantech might not be the best but at least it works!! pretty quite too.

    Many thanks

    Bill H
     
    Skavenger, Oct 23, 2005
    #4
  5. Bill H

    Paul Guest

    The latest standard for ATX power supplies, splits the 12V into
    two separate circuits. The ATX 12V 2x2 connector, which powers
    the processor, has its own 12V feed. The rest of the 12V loading,
    which would be fans, disk drives, aux video card feed and so on,
    is powered by the other 12V circuit.

    In any case, the 5V 35A rating is good for your current board, so
    there should not be a problem.

    Paul
     
    Paul, Oct 24, 2005
    #5
  6. Bill H

    Skavenger Guest

    Cheers for all the info

    Ta
     
    Skavenger, Oct 28, 2005
    #6
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