Forgot to plug in the two EPS 8PIN power - is the motherboard okay?

Discussion in 'Processors and Motherboards' started by traderjay, Oct 6, 2017.

  1. traderjay

    traderjay Member

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    I've been building PCs for years and this dual Xeon system is causing me to make every single rookie mistake conceivable. Last night I was getting tired but decided to keep troubleshooting my problematic system (issue found). I forgot to plug in the two EPS 12V 8PIN power on the X10DAX and powered the system on.

    Was able to boot into windows but running a rendering program caused BSOD, and I powered the system off and found out I left the two power cables unplugged. I hope the motherboard or CPU is not damaged?

    UPDATE: ALL PROBLEM RESOLVED WOOOOHOOOOO!

    Almost gave up and decided to plea for help online and an ex-lieutenant from the US Navy nuclear forces on anandtech saved my sorry butt. On a late Friday evening, he looked every every screenshot of my bios settings and told me to change two obscure XEON specific power saving features and it magically cleared up ALL my problems.

    The following two are disabled on the BIOS:

    - Disable C6 State Reporting
    - Disable Spread Spectrum
     
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    Last edited: Oct 27, 2017
  2. Marsh

    Marsh Moderator

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    I do that all the time, but I am surprised that the SM board would even power up to post, or even boot windows 10
    Usually the motherboard and monitor would just stare at me with a blank look.
     
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  3. K D

    K D Well-Known Member

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    Depends on the CPU and the load Ive done it once with an E3. The workstation ran fine for a few days as I was just doing some light web browsing. It started BSOD ing whenever I opened a large Visual Studio project. Several reinstalls later when I finally decided that it was not a software issue and opened up the case, noticed that the 8pin was not connected.
     
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  4. traderjay

    traderjay Member

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    So I guess its safe to say no permanent hardware damage?
     
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  5. Evan

    Evan Well-Known Member

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    Unlikely any issues
     
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  6. wildpig1234

    wildpig1234 Well-Known Member

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    probably fine. well, did you plug the 2 eps cables back in and test it out? surprised it even booted.
     
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  7. keybored

    keybored Active Member

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    X10DAX manual has this language in it:
    If the thing doesn't immediately crash and burn I'm not sure how they would tell, but I guess if it does then the evidence would be fairly easy to find...
     
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  8. funkywizard

    funkywizard mmm.... bandwidth.

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    I suspect this is a bit of CYA on their part, just in case something really bad happens, they can say they told you so. More importantly, they want to make sure you don't intentionally skip plugging it in, so having the warning be especially dire, hopefully will encourage people to listen and do the right thing.

    I would -expect- it to be fine (no permanent damage), but you never know.
     
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  9. Terry Kennedy

    Terry Kennedy Well-Known Member

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    I'm not sure why they don't enable a POST warning for it - all of the ATI/AMD video cards I've seen display an "auxiliary power not connected" message on their output if the card is powered up without the PCIe auxiliary power cable.

    It would be easy to do - just connect one of the 4 EPS12V to a sense input instead of to the 12V bus - the 3 remaining 12V pins in the EPS12V can carry over 60A by themselves.
     
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  10. traderjay

    traderjay Member

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    The motherboard is fine thankfully - thanks all for the responses.
     
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  11. T_Minus

    T_Minus Moderator

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    That's great :)
     
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  12. funkywizard

    funkywizard mmm.... bandwidth.

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    There could be many reasons for that. A simple one is, not realizing this was a problem until after the specs were finalized and a large production run had completed. Updating the instruction manual would be far cheaper than scrapping thousands of motherboards.

    Another possibility is that using one of the pins for sense is outside of the ATX spec. Even though the wiring and plug type should be capable of far more power than will be drawn from the cable, this does not mean the power supply on the other end is capable of delivering it. The EPS 4 pin is required to be able to deliver 144 watts, whereas the spec for the EPS 8 pin is required to be able to deliver 288 watts. So if a power supply has one of those connectors, to be ATX compliant, it needs to be able to supply that amount of power, no more. So even though the wiring and connectors should be capable of far more, there is no guarantee that a power supply will deliver sufficient power over 3 pins vs 4.

    A complication there is, which pin do you make the sense pin? On lower power power supplies, you may only have a single 4+4 EPS connector. So long as you're using lower-wattage CPUs, this will work fine plugging one 4 pin into one 8-pin EPS, and the other 4 pin into the other 8-pin EPS. Problem being that if you do this, pins 1-4 will be populated on one EPS connector, and pins 5 - 8 populated on the second one. So which pin do you use for sense, with no standard on this? Also, keep in mind on a 4-pin, 2 wires are 12v and 2 wires are ground. If you take away one of the wires, you may be reducing the total safe power delivery by as much as 50%, not by 25%. As above, a 4-pin connector plugged into an 8-pin EPS is allowable so long as you don't install a high-wattage CPU.

    To be clear, I actually do agree with you -- if this is a real problem, supermicro should have solved it in software or hardware. And if it's not a problem, I would strongly prefer they not scare-monger. My point is more to the portion of your statement "I'm not sure why they don't....." -- I'm not sure either, but there are more than a handful of possibilities.
     
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  13. Terry Kennedy

    Terry Kennedy Well-Known Member

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    Sure, but there's always the next design. Supermicro has been putting "Stop! You must connect power to these two connectors!" stickers on the motherboard EPS12V connectors since at least the X8 series (2009?).
    • This was a simple design idea designed for the minimum amount of changes to motherboard layout and fewest additional components. 2 alternatives that quickly come to mind are diode(s) between the EPS12V connector and the motherboard 12V bus and the same voltage sense, but this time all of the EPS12V pins are connected together as is done now, or measuring voltage drop across a shunt, like a multimeter does to measure current. Again, this is something that has been done on video cards for ages, so there are proven designs out there.
    • The power supply had better have all of its EPS12V power pins on the same bus (if "bus" means separate, internally regulated 12V sections - normally inside the supply all "buses" of a single voltage eventually go back to the same regulator stage). Otherwise, the supply will have its multiple buses connected together simply by plugging the EPS12V cable(s) into standard EPS12V motherboard connectors. See Section 5.4 of the EPS12V spec.
    • 288W is 24A at 12V. That is barely more than the rating for a single 16AWG conductor. 3 * 16AWG gets you 792W. As you say, the conductor isn't the only limitation. The Molex pin for the EPS12V connector is rated for 11A. So 3 of them gets you 396W at 12V.
    Allowable by typical usage, or allowable as per the spec? The spec says:

    "Processor Power Connector
    STATUS: Required
    Connector housing: 8-Pin Molex 39-01-2080 or equivalent
    Contact: Molex 44476-1111 or equivalent"


    As I expanded on above, "stealing" a pin for sense is a very simple implementation and there are others which still allow all of the pins to carry current and still provide the feature. Again, video cards have been doing this for years.
     
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