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Fans running with computer unplugged?!?

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Apr 1, 2012
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Motherboard
Gigabyte Z390 M Gaming
CPU
i9 9900K
Graphics
Radeon RX580 4gb
Mac
  1. iMac
  2. Mac mini
Mobile Phone
  1. iOS
Ok, I've got a weird gremlin going on here. Recently I noticed that my video card and power supply fans would continue running when I put the computer to sleep. Made a little noise, but they honestly spun pretty slow so I didn't worry about it. Then, today, I powered the computer off to swap a hard drive, and I noticed the fans were going when the computer was powered off. Weird. Then I unplugged the computer, expecting the fans to stop, but they didn't.

Huh?

Let me reiterate: My computer is powered off and unplugged from power. The GPU and PSU fans are still spinning.

So I pulled the DVI out of the video card, and they stopped. WTF? Plugged it back in, they started up again. The computer is still disconnected from power.

What the hell is going on here?

This is on the "Desktop 2" in my signature, video card is an Asus GT750. My monitor is a Samsung S27A850D, 27" 1440p, hooked up to both desktops with proper dual link DVI's. Turning off the monitor doesn't stop the fans from going, or even unplugging the monitor from power.

*edit* Turns out, disconnecting the DVI from Desktop 1 stops the fans going in Desktop 2.
 
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Honestly, I've never heard of anything like this. Pin 14 of DVI-D does provide +5v but I don't know if that's even enough to power the GPU fan and the power supply fan...
 
So, after I swapped some parts around between the two machines, it gets a little weirder.

I swapped CPU's, drives, and video cards between the two, basically so the gaming machine could be on the MSI and the Hackintosh could be on the Gigabyte board (great move, the MSI was terrible for OSX) and so I could upgrade to Sierra and clean out the cobwebs blah blah blah. Also it allowed me to have 32gb ram on the Mac which is a great boost for Protools/Logic/etc.

TLDR; The machine with the GT750 is now in a different case with a bunch of red LED fans, that now glow whenever the DVI is plugged into both machines, STILL with no power connected. Fans still go on the video card - they spin slow, probably 200rpm or less, but they alternate back and forth between one fan and the next. One of the case fans spins, the others just light up or twitch a little. PSU fan doesn't move in this one (different PSU from before). Still, it's lighting up 5 LED case fans, spinning one of them, plus alternately spinning the GPU fans.

It's too bad I don't have an easy way of patching a multimeter in between so I could measure how much amperage is flowing. Also, I wonder if using a Displayport cable on one machine would "fix" this problem, as DP only has 3.3v therefore the two computers should be better isolated from each other within the monitor.
 
This has to be the weirdest story I've heard about in a long time. lol. I wish my computer could run without being plugged in...
 
Lol yeah, it'd save me some space on the powerbar!

Made a video:
 
I just checked my system...

One Dell P2715Q connected (1) my Skylake system via DisplayPort and (2) my HP Elite 8300 via HDMI (with HDMI to DVI-D adaptor on the computer end). I'm typing this on my Skylake system and my HP is off. The GPU fan is not spinning on my HP.
 
Update: I tried plugging in a different computer to the same DVI, and it doesn't have the same problem. With my old Mac Pro on the other end it has the same problem, so I suppose I can rule out Desktop 1 being the problem. In addition, with Desktop 2 plugged into the onboard DVI, it doesn't have the same problem. So I guess that means I can blame my GT 750 card?
 
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