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  1. #1
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    ATX 12 V Power Connector on motherboard

    Major Newbie here needing help.

    I plug in the 24-pin power connector for the main power and everything starts up fine; however, when I plug in the 4-pin connector that powers the CPU fan and hit the on button, I get a flash of energy and then nothing.

    Any clues as to why this is happening?

  2. #2
    Training for Bankai JPMiller's Avatar
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    Hello and welcome to Techimo...
    From this point on you should always give us a little more info...
    Backround,... type and model of components, etc...
    I'm aware of no 4 pin power connector for the CPU fan...
    Are you refferring to the 4 pin Motherboard connector from the power supply that plugs into the motherboard?
    Last edited by JPMiller; June 15th, 2006 at 03:13 PM.

  3. #3
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    Okay. I have a 24-pin that is the main power supply for the mobo and the other one I have is 4-pin block that the mobo manual says is an ATX 12V power connector. Now, the very first time I had this plugged in, everything worked including the CPU fan. I turned on the computer and then had to shut it down. When I came to it later, it would not turn on. When I unplug the 4-pin block, the computer will turn on; however, the CPU fan does not work. I therefore assume that this 4-pin block is the 12 volts that allows the CPU fan to get it's energy as the main power does not seem to do this. Below is a site with the picture of my mobo.

    http://www.tigerdirect.com/applicati...953314&CatId=0

    It is the 4-pin block kitty-korner to the CPU. I just assumed since I had a plug for it it should be plugged in. Anywho, if I don't plug it in, then the computer will run, but I get no power to the CPU fan, thus is my problem.

  4. #4
    Millwright stroyal's Avatar
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    If it does power the fan, it is not the only thing it powers, it also adds power to the the CPU. It should have 2 yellow wires, and 2 black. If you plug it in any way but the right way it will short out the power supply. Unpluging the power supply should reset it.

    Does the CPU heat sink get warm, when it starts and the fan isn't running?
    Last edited by stroyal; June 15th, 2006 at 05:23 PM.

  5. #5
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    Yes, you have the right plug. And it is plugged in the only it can be. However, I can also tell you that it is an 8-pin plug that can be separated into two 4-pin blocks. I have noticed in another thread that someone mentioned using an adapter that the 8 would plug into and the 4 into the board, but then they said the ATX status of the board did not work. Perhaps I need a different power supply or is that not the case?

  6. #6
    Millwright stroyal's Avatar
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    The only 8 pin connector I know of is for 945X chipset or higher (dual core) socket 775.

    http://www.tomshardware.com/2005/11/...01/page19.html

    The one with the 2 black and the 2 yellow wires should say P3 on it.

    http://www.tomshardware.com/2005/11/...01/page20.html

    I would be surprised if you need another power supply, that one sounds like it has everything but the kitchen sink.
    Last edited by stroyal; June 15th, 2006 at 05:38 PM.

  7. #7
    Millwright stroyal's Avatar
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    Looking back at your post, You said "I get a flash of energy and then nothing".

    To me that sounds like a short, and the circuit breaker in the power supply is tripping like it is supposed to.

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    Sorry didn't get right back at ya, company showed up. So, a short in the power supply or motherboard? Is there some way to fix that or do I need to return the item, whichever it is.

    Thanks for your help. Hope to hear from you soon.

  9. #9
    Millwright stroyal's Avatar
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    It's more likely that somthing is plugged in wrong of the board is shorting out against the case.
    Assemble the board outside the case on a wooden table or somthing non cocductive, ( not an antistatic bag). You only want motherboard, power supply, 1 stick of memory, CPU, video card, and monitor for the test. You don't need any drives or other expansion cards to see if it will start.

    If you took it to a computer shop, the way they would test things is to try each of your parts in another computer or try parts that they know are good in your computer.
    Last edited by stroyal; June 16th, 2006 at 09:13 AM.

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    Okay, I took the mobo out and attached just the things you mentioned. I get no power with the 4-pin plugged in. If I take out the 4-pin, I get power, but I get no video.

    Any more ideas?!

    Thanx!

  11. #11
    Human voltmeter DanU's Avatar
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    Can you tell us what the rest of your components are? Video card? Power supply brand and model? etc.

    The 4-pin connector supplies power to the CPU. If the computer doesn't power up with this plugged in, this sounds like the power supply can't handle the load of the CPU, or there is a short somehwere and it is shutting itself down.

  12. #12
    Ultimate Member zepper's Avatar
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    Lightbulb

    Is your PSU split 12V rail or single 12V rail? Perhaps you need a single rail PSU. An off-brand (or an older design) mobo like that can expose a flaw in the split-rail PSU system - you can't parallel the rails within a component (the mobo being the most likely spot where that might happen). In older designs, ALL the 12V in a mobo could be connected to a single bus (i.e. all the yellow wires would be connected to the same copper within the mobo). In newer designs, there can be several, isolated 12V busses: one for general use (ATX connector), one for the CPU(s) thru the 2x2 or 2x4-pin ATX-type connnectors, and even a third for fancy video cards. That way the 12V rails of a split-rail PSU are kept isolated.

    A way to check if your mobo has a single 12V bus inside it is to: disconnect all external connections to the mobo and remove all add-on cards, take a DMM (digital multimeter) set up to read resistance, set it to the 1 (or low) Ohm scale, read across a 12V pin in the ATX connector and a 12V pin in the P4 (2x2-pin) connector. If the reading is zero Ohms or near, then you have a single-bus mobo. If the resistance reads quite high or 'infinite', then you have a split-bus mobo which is safe for split-rail PSUs. Or if you don't have a meter (every computer hobbyist should have one - a decent one (Craftsman) is often on sale at Sears), call your mobo's tech support to find out.

    If you find you need a single-rail PSU, I have a nice Fortron for sale in the Traders section here and ResellerRatings.

    .bh.

    Split-rail PSUs - yet another bright idea from Intel... Go Zippy!



    PS: The above is another reason for a listing of components (make & model) in the initial question. As it is, we can't tell if the split-rail thing might even be a possibility as we don't know what your PSU is. .bh.
    Last edited by zepper; June 16th, 2006 at 04:26 PM.
    "Our freedom depends on five boxes: soap, ballot, jury, witness; and, when all else fails, Ammo. " ?author?

  13. #13
    Millwright stroyal's Avatar
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    Good one, I never thought of that.
    The label on the power supply should show 2 +12v rails also.

  14. #14
    Ultimate Member EXreaction's Avatar
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    Ah, he isn't talking about his powersupply being the problem. its after he plugs in the 4 pin FAN connector that he gets problems.

    Sounds like the fan could be bad and shorting. And yes, they do make a 4 pin fan connector for the cpu, I have seen it on LGA 775 mobos.

    EDIT: Unless he was confused at first, ah, now I am confused, which is it, the plug from the power supply, or the plug from the fan?
    Last edited by EXreaction; June 16th, 2006 at 05:22 PM.
    "The problem with quotations on the internet is that the sources are hard to verify" - Abraham Lincoln

  15. #15
    Millwright stroyal's Avatar
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    Quote Originally Posted by EXreaction
    Ah, he isn't talking about his powersupply being the problem. its after he plugs in the 4 pin FAN connector that he gets problems.

    Sounds like the fan could be bad and shorting. And yes, they do make a 4 pin fan connector for the cpu, I have seen it on LGA 775 mobos.

    EDIT: Unless he was confused at first, ah, now I am confused, which is it, the plug from the power supply, or the plug from the fan?
    It's the P3 plug for the CPU, and it's sounds like the circut breaker in the power supply is tripping.

    Quote; I get a flash of energy and then nothing.

    edit; I know for a fact, that's what happens when the p3 is plugged in wrong, and it can be, just the latch won't line up and work .

    It causes a short because the +12v line hooks to ground and the power supply trips so fast that you can hardly here it. On my computer the CPU fan would just jiggle. Stupid me did that once. Any other short would do the same thing.
    Last edited by stroyal; June 16th, 2006 at 05:55 PM.

  16. #16
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    You're not trying to plug a floppy drive power connector into a fan power OUTPUT on the board, are you?

  17. #17
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    No.

    Is it possible that the power supply is too powerful for the motherboard? Is there a rule as to how much wattage the mobo and/or cpu can handle?

  18. #18
    Ultimate Member zepper's Avatar
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    Power of PSU is irrelevant as long as it's enough - you could put the PCP&C kiloWatt unit on there if you could afford it... Mobo only takes what it needs. Please inform us to the make/model of your PSU as has been asked several times above.

    .b h.
    "Our freedom depends on five boxes: soap, ballot, jury, witness; and, when all else fails, Ammo. " ?author?

  19. #19
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    Quote Originally Posted by UCLAMouse
    No.

    Is it possible that the power supply is too powerful for the motherboard? Is there a rule as to how much wattage the mobo and/or cpu can handle?
    No. Laws of physics apply. The current flow (and consequently, the wattage) is a function of the consuming end, not the supply.

    Ex. When you run a 100W light bulb on a 230V 16A circuit, you're not getting 230V x 16A = 3680W, you're going to get 100W. Same thing for the computer.

  20. #20
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    Quote Originally Posted by zepper
    Power of PSU is irrelevant as long as it's enough - you could put the PCP&C kiloWatt unit on there if you could afford it... Mobo only takes what it needs. Please inform us to the make/model of your PSU as has been asked several times above.

    .b h.
    Aspire 680W Beast Power

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