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Thread: MOBO-PSU Fatal Combination




  1. #1
    Join Date
    Aug 2005
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    Default MOBO-PSU Fatal Combination

    I have this serious problem.<o:p></o:p>

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    I have an abit kx7-333R mobo, which has done a great job … now I bought a new psu … Coolermaster 550W.<o:p></o:p>

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    Now it wont power up with the new psu. The fan on the psu spins up for only half a second and stops running. No action on the mobo exept for the standby power indicator (yellow indicator on the mobo). It lights up so the +5VSB supplies power to the mobo. So when I press the power button the power indicator (green light on the mobo) lights up for a second, also the reset indicator lights up for a second(red light on the mobo), both indicators turn of after less than a second.<o:p></o:p>

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    My old psu still works with this mobo.<o:p></o:p>

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    When I took out the Coolermaster and connected it to a new recent mobo it works. So it’s not the psu that’s the problem or my kx7-333R. The problem is when both are connected to each other that gives the problem.<o:p></o:p>

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    Now, the ONLY difference I can find between these two PSUs is that my old psu has a “-5v” rail. Maybe the kx7-333R needs it for the Power Good Signal so the Power On Signal is sent via the mobo.<o:p></o:p>

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    I have tried everything and spent a couple of days reading on the internet for similar problems.<o:p></o:p>

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    Took my mobo out of the case … unplugged all my pci cards, also my videocard, memory, replaced cpu and heatsink, shorted the green wire to any of the black wires in the power connector so it would fire up …. NOTHING seems to be working with this psu attached to this mobo.<o:p></o:p>

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    I hope anyone can help me to solve this problem.<o:p></o:p>

    <!--[if !supportEmptyParas]--> <!--[endif]--><o:p></o:p>

    Abit KX7-333R<o:p></o:p>

    Coolermaster RealPower 550W<o:p></o:p>

    AMD Athlon 2600+<o:p></o:p>

    TWINX1024-3200XL 1GB<o:p></o:p>

    Matrox Millennium G400<o:p></o:p>

    1x Maxtor Quantum Fireball 541DX<o:p></o:p>

    1x PX-708A/UF<o:p></o:p>

  2. #2
    Join Date
    Feb 2003
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    Fincastle, IN, USA
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    Default Re: MOBO-PSU Fatal Combination

    All PSU's have a -5v rail. Most likely you have acquired a malfunctioning PSU that needs to be exchanged. That can be easy, depending on where it was purchased.

  3. #3
    Join Date
    Aug 2005
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    Default Re: MOBO-PSU Fatal Combination

    Quote Originally Posted by amd_man2005
    All PSU's have a -5v rail. Most likely you have acquired a malfunctioning PSU that needs to be exchanged. That can be easy, depending on where it was purchased.
    Most recent PSU's don't have the "-5V"raail. Negative rails -5V and -12V are seldom used for anything in modern PCs.

    Some of the power supply designs, such as the small form factor (SFX) design, no longer include the –5v output for that reason. The only reason it has remained in some power supply designs is that –5v is required on the Industry Standard Architecture (ISA) bus for full backward-compatibility.

    Although –5v and –12v are supplied to the motherboard via the power supply connectors, most motherboards normally uses only the +3.3v, +5v, and +12v. The –5v is simply routed to the ISA bus on pin B5 so any ISA cards can use it. Today, though, not many do. However, as an example, the analog data separator circuits found in older floppy controllers do use –5v.

    The motherboard logic normally doesn't use –12v either; however, it might be used in some board designs for serial port or LAN circuits.

  4. #4
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    Default Re: MOBO-PSU Fatal Combination

    If you know all that..then why are you asking us what the problem is...?

  5. #5
    Join Date
    Aug 2005
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    Default Re: MOBO-PSU Fatal Combination

    The problem is still there ...

    If it's not the -5V .... is it possible because the PSU is a dual 12V rail and the Abit regulates CPU power off the 5V rail.

    If the CPU regulates it's voltage from the 5V rail, can the overvoltage protection kicking in because of the crossload? The heavy 5V load is probably lowering the 5V below threshold and jacking 12V above threshold and is the combination than possible causing the power supply to trip?

    If someone can help me with this problem ...

    Tnx!!

  6. #6
    Join Date
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    Default Re: MOBO-PSU Fatal Combination

    That shouldn't make a difference. Are you absolutely sure you have everything plugged in? I would give Google a look and see if anyone else has had this issue, if not I would send it back and get a new one and see what happens.

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