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Mobo won't power - 8 pin CPU ATX 12v

#1
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5/5/07 at 3:37am
  • Joined: August 2001
  • Post Count: 349
I'm building a new computer and I'm having the most difficult time in the world trying to get this thing to start up.

First off, I'm using the EVGA 680i motherboard which is using the Nvida chipset. For the CPU, I'm using an Intel E6700 Core 2 Duo processor. The power supply is a 750w Thermaltake.

Now according to the motherboard manual that can be downloaded online, you're supposed to connect 2 power cables: the 24 pin ATX power cable and the 8 pin ATX 12v power cable which supposedly supplies power to the CPU.

Now here's what I've found: I can connect the 24 pin ATX power cable and the entire computer will turn on: the fans and everything else is running, all except for the CPU which isn't receiving power. As soon as I plug the 8 pin ATX 12v cable that's supposed to power the CPU, the computer will no longer turn on. It'll turn on for a milisecond and instantly turn itself off.

Reading the manual further, it says that even though it's strongly recommended to use all 8 pins, you can get away with using only 4 so I used a 4 pin connector instead, just to see if perhaps I can get the system to boot but I get the same results.

So then I thought, maybe I can connect only 20 pins of the other cable (the 24 pin cable) and the 8 pin ATX 12v cable for the CPU but again, I get the same exact results.

The CPU is seated correctly (I've double checked). I don't know what's wrong.

Can anyone please help me to correct this problem? Any help would be greatly appreciated. I've spent tons on this computer already and I can't return any of the parts now.
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#2
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5/5/07 at 8:41pm
  • Joined: July 1997
  • Post Count: 6,788

Re: Mobo won't power - 8 pin CPU ATX 12v

Quote:
So then I thought, maybe I can connect only 20 pins of the other cable (the 24 pin cable) and the 8 pin ATX 12v cable for the CPU but again, I get the same exact results.

Yeah, don't ever do this. Very, very bad, especially if you have a higher end Nvidia card in the PCI-E slots. It's a great way to completely toast the board.

OK, if you're getting it to flash on/off again, there are a few things that can cause it:

(1) The thermal sensor detects the CPU fan is not plugged in or seated properly.
(2) The CPU is not seated properly.
(3) A video card is not in the primary #1 PCI-E slot, or has insufficient power if it requires a PCI-E power connector attached.
(4) You have a grounding issue, where the board is grounded to the case.
(5) If you're using any of these cards, you need this PSU or HIGHER.

8800GTX=600W (ideally) or HIGHER.
8800GTS=550W (ideally) or HIGHER
79xx=500W or Higher
ATI 1950X Series = 550W or higher



Good luck, post back if you run into anything!
My Current DVD-Profiler


"I've been Ostrafied!" - Christopher, Sopranos 5/6/07
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#3
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5/7/07 at 5:17am
  • Joined: August 2001
  • Post Count: 349

Re: Mobo won't power - 8 pin CPU ATX 12v

You were right Chris. It was a grounding issue. Apparently one of the metal pins that I screwed into the case for support was touching the M/B in the wrong place causing the issue. As soon as I took it off, it was fine and was able to power on immediately with the 8 pin connector and the 24 pin connector. It's running amazing well now, except that there is no sound. I've spent hours on trying to get the sound to work and it just doesn't. I've even called tech support and they couldn't figure it out either.
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#4
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5/7/07 at 8:52am
  • Joined: July 1997
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Re: Mobo won't power - 8 pin CPU ATX 12v

Forget eVGA's instructions on getting sound.

Here's the driver:

http://www.realtek.com.tw/downloads/...&GetDown=false
My Current DVD-Profiler


"I've been Ostrafied!" - Christopher, Sopranos 5/6/07
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#5
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9/7/09 at 9:34pm
  • Joined: September 2009
  • Post Count: 2
I have the same problem. My motherboard is ASUS P5W DH Deluxe, PSU is XION Supernova 600W ATX 2.2. The motherboard won't power on if the 4pin 12V CPU power is connected. It will turn on if disconnected. I swap to an older PSU, Enermax 450W ATX 1.2 and the mobo powers up. I tried the Xion on a P4P800 Deluxe and the same problem occurs. Is the problem with the PSU?
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#6
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9/10/09 at 8:19pm
  • Joined: September 2009
  • Post Count: 2
I found out how to solve the problem. If the pc won't power on, I unplug all the attachment peripheral power cables from the PSU, the pc will turn on now, Then I turn off the pc and re-attach all the peripheral power cables and turn on the pc again. This works for me. I think it's a grounding issue, one of the cables may be grounded.
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