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PSU Weird GPU behaviour with 8-pin connected...

Discussion in 'Hardware' started by LennyRhys, 18 Aug 2014.

  1. LennyRhys

    LennyRhys Oink!

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    So after returning from holiday I thought I'd get the "proper" 8-pin connector hooked up as I'd been using a 6-pin to 8-pin adapter whilst on holiday. So about an hour ago I switched to one of the 8-pin to 8-pin modular cables that shipped with my TT PSU.

    1st attempt, power up fine, all PSU LEDs green, but black screen, no POST (?)
    2nd attempt, same again, and I notice that GPU fans are spinning up, dying down etc.
    3rd attempt, try other 8-pin cable, exactly same again
    4th attempt, try another 8-pin output from PSU, same again

    So I went back to the 6-pin cable/adapter I'd been using and PC booted up fine first time. So there must be something wrong with the 8-pin cables, right?

    So I tried one of the 8-pin cables with the adapter, and same again - no POST, black screen
    Went back to the working combo, and *gasp* no POST, black screen
    WTF?!

    Reset CMOS, and now I have a 6-pin and 8-pin cable (both TT modular) working fine - y'know, the combo that refused to work the last 6 or 7 times I tried it, lol.

    So what do you guys think... possible GPU problem, PSU problem, or just one of these annoying quirks that can never be explained?

    I've run umpteen stress tests, both GPU and CPU, and have a hexcore CPU running at 4.3GHz currently, and there are no problems with my system, so I'd say it's very unlikely to be the PSU. PSU is almost 4 years old but iirc it has a 7 year warranty (which I probably voided by replacing the PSU fan, lol!).
     
    Last edited: 18 Aug 2014
  2. jinq-sea

    jinq-sea 'write that down in your copy book' Super Moderator

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    I wonder if you have unearthed a most strange quirk - could have been lugging the system around, perhaps?
     
  3. LennyRhys

    LennyRhys Oink!

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    I was thinking that, but I'm not sure moving the PC around would affect the integrity of non-moving parts.

    To get to the bottom of this I'll have to test each of the four PCI-E outputs systematically as it's possible one of them is misbehaving. Despite all the stress testing I've done recently, I'm not going to be happy until I investigate this a little further, because the last thing I want is the graphics card giving up when I'm in the middle of something. Time to test each of the PCI-E outputs.
     
  4. Big Elf

    Big Elf Oh no! Not another f----ing elf!

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    You've probably done this but check each pin in the connectors, PSU and graphics card carefully making sure none are bent or damaged.

    The 2 extra wires on an 8 Pin PCI-E connector are ground/sensor cables. They're supposed to indicate to the graphics card (which is expecting 150W from the 8 pin connector) that it's available.

    Edit: You just have a single 770GTX connected?
     
    Last edited: 18 Aug 2014
  5. LennyRhys

    LennyRhys Oink!

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    Yeah I suspected that there might be something up with the pins, but it's all pristine.

    I've tried to reproduce the problem but have been unable to. I wonder if it's this beta BIOS file playing funnies with my system, but that wouldn't explain why the problem only presented exactly when I chose to change my PCI-E cable. Weird!

    And I did wonder about the extra two pins on the 8-pin cable as my EVGA 680 worked perfectly (and even overclocked nicely) with a 6-pin instead of the "required" 8-pin.
     

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