How can compnents not connected to a powered power supply have power?

[wareyore]

I'm trouble shooting an issue with my EVGA SR2.

Back story: The PC appears to have shut off by itself the other day. No power loss in the house or other issues we’re aware of. I turned it on and after a few minutes of normal operation it shut itself off like a light switch.

I thought I had a problem with the MB, so I turned it back on and started checking settings. Everything looked normal then it shut off by itself, again.

Restart, check temps and see if heat is building on anything quickly. Don’t see a temp problem. Poof, it shuts off. Restart, get to BIOS check settings there, poof, shuts off. Boot back into BIOS quickly load default settings to remove the OC and custom voltages. Boot into OS, looking good, then poof, all off. Try again and look for the log files nothing there, then poof, all off. Power off occurs randomly and not while I'm doing anything specific.

Open the panel and check for smells or signs of smoke. Nothing. Turn it back on and notice one of the four CPU fans on one of the Noctuas stops spinning. Three other fans are fine. Inspecting further I see the motherboard chipset fan is not spinning and the vid card fans are not spinning.

Now I think the motherboard could be failing, but, I decide to rule out power supply by swapping with a spare. I disconnect the G2 from the wall and pull the 24 pin, two 8 pin and three 6 pin connectors from the extensions leading to the board. I pull the sata power for the boot drive, as well, along with the vid cards power. I pull one of the vid cards out to reduce power draw and double check the cards in another system. I leave the remaining drives (12 total), the B-ray drive and case fan controller connected to the G2’s, now powerless, connectors.

I connect a Seasonic 750 to the motherboards 24 pin directly and connect its 8 pin to the extension, use its 4 pin for a partial 8 pin connection, connect the 3 PCI 6 pin connectors to their extensions, using one molex Y adapter, connect the vid card and primary hard drive to see if I can run it without crashing. I turn it on and the system is running again! No sudden shut off. I am able to work normally.

Here’s what I don’t understand: I still have my RAID array’s up, case fans running and the BD drive works. I expected these all to be without power since none are connected to the Seasonic 750. I look in the case and the fan for the G2 is spinning. So, there is still no power plugged into the G2 at all. Is the Seasonic powering all this through the G2’s wiring? !?! Is there a short in the board or case?

There is nothing connecting these two power supplied to each other so I can’t figure out why the components that are not connected to the Seasonic 750 power supply are powering up.

 

[GiGaBiTe]

It sounds like that case is pretty busy with a rats nest of power wires in it, you could have missed a power wire somewhere or have something crossed.

 

[LFaWolf]

If you use 8 or 24 pin power extension cable, those might be the problem. Try to connect directly using the cables from the PSU.

 

[wareyore]

If you use 8 or 24 pin power extension cable, those might be the problem. Try to connect directly using the cables from the PSU.

This may be the culprit. Rebuilt the entire system weeks ago and it was OK until Saturday. Boom - shut down and wouldn't stay on for more than 2-3 minutes.

Swapped the 24 pin connection with a known good PSU and left everything else in place on the old one. Started the old one up then the main PSU and everything ran ok. Pulled the extension off the old one and reconnected it and so far so good. Looks like it may have been a bad 24 pin extension causing the issues.