AMD 6970 fried my mobo!

Discussion in 'Videocards - AMD Radeon' started by Unfettered, Jul 30, 2011.

  1. Unfettered

    Unfettered Banned

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    Ok, so I bought a 6970 and plugged it into my m3a79-t deluxe motherboard about 7 or 8 months ago. Plugged in the power cables and tried to boot up and it fried my motherboard. I RMA'ed the mobo and returned the video card for a full refund but never actually was able to determine what had caused the problem.

    Today I'm doing research on upgrading again and I was reading the AMD system requirements for the 6970, and they specify one 8pin 150w cable, and one 6 pin 75w cable to power the video card. My power supply IS on the approved list for this card, its a tx850w Corsair.

    This said my 8 pin cable is plugged into my motherboard, and my PCI-e power cables have this extra wire hanging off of them with an extra 2 pins to equal 6, or 6+2 or 8 pin.

    So the questions I have for those of you with more technical experience than me is. Do these PCI-E cables with the extra 2 pin option put out 150 watts when used as an 8 pin? Or do they still only put out 75 watts? Could this be how the 6970 fried my mobo?
     
  2. Psycho101

    Psycho101 Master Guru

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    Yes, the 6+2 pin PCIe cables are fully functional 8pin PCIe power. They're just split for convenience, allowing one to use cards with twin 6pin PCIe power more easily etc.

    The extra two pins are both grounds and allow 150W to be safely drawn from the three +12V pins in conjunction with the three grounds of the 6pin connector plus the additional two grounds from the +2 section.

    There's no functional difference between the two types.
     
  3. Unfettered

    Unfettered Banned

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    Ok cool, at least now I know.

    Any idea on what could have caused my mobo to fry when I installed and booted up with the 6970?

    One thing I noticed when I got the RMA back from asus was that the south bridge on CPU-Z shows up as a 700, but the m3a79-t deluxe is supposed to be a 790fx/750 south bridge. Not sure if it was always saying that, if cpu-z just shows the wrong info, or if that was the component that fried when I tried to run the 6970. Unfortunately Asus didnt specify what components they replaced, only that there was 2 of them.
     
  4. Psycho101

    Psycho101 Master Guru

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    I'm not sure to be honest.

    There could have been damage to the PCIe slot, or conductive debris could have gotten inside it, causing a short circuit. It could also have been conductive debris falling on the mobo or under the board inbetween it and the motherboard tray.

    Another definitely possible scenario would be that it was jus tthe board's time to die. There could have been a marginal component that spontaniously decided to go pop and caused additional damage when it did. This kind of fault is often overlooked because when something fails we (myself included) search for a rational explanation, one relevant to the situation. The act of replacing the graphics card kind of sticks in one's minds so strongly that we automatically think that was the thing that killed the board. It's logical, but possibly not what happened.

    I would assume that what happened to you was a one off thing. However, to be safe, check your PSU PCIe connectors with a multi meter to see if they're working in spec. Also chech that the wires are relatively securely attached to the PCIe plugs and that there's no major kinks in the cabel that could have caused the wire insulation to have split. Bare wire can short on the case, even if covered by the outer sleving, it can arc.

    I've also seen AMD boards with SB750 Southbridges ID'd as SB700. For example it happens with the GA-790XTA-UD4. I'm sure it's just a BIOS quirk or incorrect detection in CPU-Z.
    [​IMG]
     

  5. flow

    flow Maha Guru

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    " So the questions I have for those of you with more technical experience than me is. Do these PCI-E cables with the extra 2 pin option put out 150 watts when used as an 8 pin? Or do they still only put out 75 watts? Could this be how the 6970 fried my mobo? "

    They will put out the watts your videocard is using. For example, you could use the cables supplied with the card and connect those to the 12v molex cables, one cable would pull enough juice to get the 75w required, the other cable 150w.
    The pcie cables are just power cables, and as already explained, the extra 2 pins are needed because of the bigger draw from the psu.

    Funny about the switching of components, I did experience this in the past with a pc, just recently bought new lamps for on our wall, wanted to use the light bulbs from the old 2 lamps, both refused to work in any of the new lamps, for sure they worked fine in the old lamps, just a second before I switched them. One of those bulbs wasn't that old either, not even dirty from our smoking and cooking.
    Still, there you go, you remove a component, replace it, and can do this numerous times, but all of a sudden the component dies, or just after one switch.
     
  6. nikitash

    nikitash Banned

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    u need to put 1x 8 pin connector and 1 x 6 pin connector ti give that HD 6970 full power.

    Although 2x 6pin power connector will deliver 150 w ( 75w each) so the extra 2 pins give more juice under load.
     
  7. Rich_Guy

    Rich_Guy Ancient Guru

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    Sounds like it wasn't connected up correctly to me, as he says he had a 6970, but then he says :-

    Now wouldn't he have already known that the 6 Pin, with the 2 Pin hanging off of it was an 8 Pin, as he would have removed them from the 6970s 8 Pin socket, when taking it back out after it blew his board. :confused:
     
    Last edited: Aug 3, 2011
  8. Jeepster50

    Jeepster50 Member

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    CPU-Z incorrectly identifies my M4A79T D SB as a 700 as well, rest assured your SB is a 750.
     
    Last edited: Aug 3, 2011

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