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Simple Motherboard Power Connection Question

Discussion in 'Hardware' started by memevertical, Apr 11, 2010.

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  1. memevertical

    memevertical Thread Starter

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    Hi everyone......

    I Installed a new motherboard on my PC. The cable that goes to the power switch button on the front is a simple 2 pin cable. And on the motherboard I connected it where it said (Power +, Power -)......but there is a problem, when I press the power button the computer does turn on fine, but when I shut down the computer, the power button's light stays on.....and the keyboard stays with the NUMLOCK light on aswell.......any ideas????

    Thanks everyone!!!!
     
  2. frankjohn

    frankjohn

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    Re check the pin connections , as a test you can try hooking up the power on to the re set button
     
  3. win2kpro

    win2kpro

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    The power switch is not polarity specific, the power LED is polarity specific, try turning the power LED connector 180°
     
  4. memevertical

    memevertical Thread Starter

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    Ok, I did some tests, and this is what I found:

    The 2 pin power cable is just to turn on and off the PC. The actual cable thats feeding the light to the power button is the USB cable inside.....how do I know this? when everything else was connected and only the usb cable was not connected there was no light on the power button.

    Now, here's the problem again.....if everything is connected, when I connect the pc to the wall, immediately the light on the power button goes on.......even if I start the pc and shut it down, the power button still has a light.......

    any ideas? Thanks!!!
     
  5. win2kpro

    win2kpro

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    I believe you either have something wired incorrectly or a board circuitry fault. There should never be anything wired with a USB cable since USB is a "weak" circuit with a USB port only being capable of +5v with 500mA.

    Most USB motherboard headers are nine pins of which 8 are used. One side feeds one USB port and the other side feeds another USB port. A USB port only uses 4 wires, i.e. a +5v, -D, +D and ground. The +5v and the ground supply the power, and the -D and +D are for the data signal. On some chassis the USB connector is a single plug that will only plug in one way. On other chassis they may use 4 wires for each USB port. If your chassis uses 4 wires for each USB port double check and make sure they are pinned out correctly.

    What is the make and model of the motherboard you are using?
     
  6. memevertical

    memevertical Thread Starter

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    Well this are the specs:

    The Pc is a gateway DX4200 and the motherboard I bought is a Gigabyte MA785GM-US2H

    Here's the scenario:

    USB cable plugged into motherboard - PC works fine, power light never goes off
    USB cable unplugged from motherboard - PC works fine, NO power light at all

    Is weird because I see that the USB cable goes to the top of the pc (where the front USB's are) and from there a cable goes to the power button. Why would they wire the light of the power button from the USB area?

    Thanks for your time and help....
     
  7. win2kpro

    win2kpro

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    Without physically seeing the arrangment I'm just guessing. From what you describe unless Gateway had problems with the +5v leads on the original board (no +5v on the USB motherboard header) and "jury rigged" the board to pickup the +5v from the front panel switch I have no idea why it would be wired like you describe.

    Also, they may have had a problem with the +5v on the front panel header and be picking up the power for the front panel header off the USB +5v line.

    What it comes down to is we don't know if they are using the +5v from the USB to power the front panel header, or if they are using the +5v from the front panel header to power the USB.

    If a manufacturer gets a shipment of boards with defective circuitry where they can "jury rig" a work around they of course will do that rather than discard a shipment of boards.

    Assuming that your new board has no electrical faults and the +5v for the front panel header and USB are being supplied internally you should be able to clip the lead going from the USB cable to the power on switch and everything should work as it is supposed to work if the front panel header and USB header is pinned out correctly.

    If you decide to clip that lead make sure you have enough wire so that if something goes wrong you can splice the wire back together. I would only clip the wire if it is a single wire and certainly don't clip the wire if it is a shielded wire. If you decide to clip the wire and everything works properly, make sure you have some heatshrink or other insulating material to insulate both ends of the clipped wire.

    I've had to "jury rig" a couple of machines where the +12v pin on the CPU cooler header was defective by picking up the +12v off a 4 pin molex connector so the machine "believed" the CPU fan was receiving voltage from the CPU header since the machine would not start without the fan connector being plugged in to the motherboard CPU connector.
     
  8. tundram

    tundram

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    the reason the light stays on with the usb connected is that some boards power the front usb off the 5v stand and are powered all the time, enabling a usb keyboard or mouse to be used to power on the system if so set to in the bios, I have an asus board that does that, also handy if you need to charge a cell phone or something with out having computer on, i use ti as a night light often with a usb lamp that a friend got me. There maybe a bios or jumper setting that lets you choose where the usb gets its power from, the 5v stby or 5v power.
     
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