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Thread: What causes this...

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    Exclamation What causes this...

    Link >> http://forums.overclockers.co.uk/sho...php?t=18546130

    He is using an OCZ 1250W with 2 x 7990's, 4770K etc.

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    What motherboard?
    "Sometimes a cigar is just a cigar" - Unknown (but sometimes attributed to Sigmund Freud)

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    Quote Originally Posted by Original Sin
    What motherboard?
    Not sure, I've just asked.
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    Excessive current draw through that connector. HD7990s you say? How heavily overclocked?

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    Quote Originally Posted by CM Phaedrus
    Excessive current draw through that connector. HD7990s you say? How heavily overclocked?
    Doesn't mention, but he's got them both watercooled, so I guess he has overclocked them, I'll find out.
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    Firstly, that's not a very smart setup, even on motherboards with additional power connectors for the PCIe slots (which are very rare for Sandy/Ivy/Haswell boards, more common for extreme series boards). Tahiti XT chips are power thirsty, especially when overclocked/overvolted, under which conditions they can easily rival OCd 480s and 580s. The PCIe slots normally supply 75W (according to specifications, usually more), the rest has to come through the PCIe connectors on the card. Which means that for some cards, under certain circumstances, something in the power delivery system gets overloaded.

    Usually, on very heavy setups (such as this one) the wires that get overloaded are the two 12V in the 20+4pin connector (and they melt), but in this case, since the four GPUs are on two cards that make use of two slots, those two wires deliver ~150W watts to the cards (the rest comes through the PCIe connectors on the cards themselves), as opposed to four GPUs on four different cards (4x PCIe slots, 300W+ and you have a nice 20+4pin meltdown).
    The fault here is hard to attribute, it's not the PSU (though having thicker wires usually helps, and there are differences in this regard, between PSUs). I would say that like in similar cases (with melted wires/connectors and, sometimes, fried electronics as a consequence), the issue is a poorly thought out system. Having four GPUs on a platform like that can be ok for Mining or similar stuff, but overclocking them and then benching (or doing other very GPU intensive work) can lead to such outcomes. If you're gonna' overclock multiple high end, powr thirsty GPUs, you might as well get them on individual cards and put them in a mobo designed to cope with such gear (additional PCIe connectors on the mobo itself, to feed power to the PCIe slots).
    "Sometimes a cigar is just a cigar" - Unknown (but sometimes attributed to Sigmund Freud)

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    Too high current or too high contacting resistance (by bad contact). Either one is possible if not both.

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    Quote Originally Posted by ssshjp View Post
    Too high current or too high contacting resistance (by bad contact). Either one is possible if not both.
    When there's a poor contact involved, it's usually a one pin affair. We've seen this many times before, it's a current overload. There's two way to look at this... you can blame AMD for putting two 8pin connectors on a card that can pull 600W+ under reasonable overclocks, or you can blame the builder for ignoring that fact and putting such cards under heavy stress. Either way, the PSU is not at fault.
    "Sometimes a cigar is just a cigar" - Unknown (but sometimes attributed to Sigmund Freud)

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    Quote Originally Posted by Nelly View Post
    That's easy:
    A very strong PSU without (usful set) OCP.

    With a single rail PSU as is used in this it is possible to draw the full power with each connector. When the power draw exeeds the limit of the connector, it may melt. Or even the cable may burn.
    That's rather common, when used beyound specifications and that's the reason you have a breaker in your house!
    With a single rail PSU you don't have this kind of protection, so when violating the specs, somthing terrible will happen...

    And by the way: Molex sais one connector can be used for up to 10A (or was it 7,5A??) So do the math...
    3x 10A x 12V = 360W. That times two (because the card uses two connectors): about/at least 720W for each card...

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    From the original poster...
    Quote Originally Posted by keikeimok
    I am using ASUS Z87 Deluxe. I am not overclocking at the moment, not even the GPU, this thing really put me on the edge. I kept looking at the plugs from the windows from time to time now and sniff on the exhaust for any smells too.
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