What would cause case fans to be powered by the HDMI cable in the GPU

Zepher

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I was working on a client's PC earlier tonight. it's an older Z97 setup, Asrock Z97 Extreme with a G3xx something 2 core CPU, Corsair CX750 and an MSI 660Ti.
I powered down the PC and 2 of the 3 case fans were still spinning, bottom case fan, and the front fan which has LED's and they were still lit.
Unplugged the power cable and those 2 fans were still spinning and the front one still lit up. thought it might have been residual power but when I stopped the bottom fan with my finger, it started spinning again.
Unplugged the HDMI cable and they turned off. I thought that was really strange. Plugged the HDMI cable back in and they started spinning and lit up.
The HDMI cable goes straight into my LG 25" ultrawide, so no hub or splitter, just a straight hdmi cable from the monitor to the PC.

Anyone else experience something like this?
 
I've seen it once on a PC with a DVI cable. Your monitor is sending power down the cable. It's a monitor thing, as you will likely see the same result with a different cable.
 
I've seen it once on a PC with a DVI cable. Your monitor is sending power down the cable. It's a monitor thing, as you will likely see the same result with a different cable.
interesting, and here I was going to say it was haunted.
 
This is the machine with the GPU removed. I also noticed that this Z97 board has an M.2 slot, pretty rare for Z97, isn't it?
it's not the fastest M.2,
1 x M.2_SSD (NGFF) Socket 3, supports M Key M.2 SATA3 6.0 Gb/s module and M.2 PCI Express module up to Gen2 x2 (10 Gb/s)

IMG_3324.JPEG
 
I've seen it once on a PC with a DVI cable. Your monitor is sending power down the cable. It's a monitor thing, as you will likely see the same result with a different cable.
It's also weird that with the GPU removed and the PC powered down but the PSU switched on that those same two fans keep spinning.
 
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That thing needs a blow job in a bad way. Seriously I've seen dust bridge circuits before and that thing is a dirtball. Outside and air compressor for the blowout.
 
Now this is really odd. I put the motherboard into my Corsair 465X case that has the case fans hooked up to a Corsair Commander Core XT fan controller that is powered by SATA power.
As soon as I plugged in the HDMI cable into the 660Ti the case fans started spinning. I thought it might just be the GPU so I installed GTX 750Ti that only uses PCIe power and it does the same thing.
So the monitor is sending enough power through the HDMI cable back into the PCIe slot and back through the PSU to power the fans on the Commander Core XT through the SATA power connector.

Also, removing the GPU and just plugging in the HDMI cable to the motherboards HDMI port and just using onboard video doesn't exhibit this behavior.
 
I've seen it once on a PC with a DVI cable. Your monitor is sending power down the cable. It's a monitor thing, as you will likely see the same result with a different cable.
It did it with an ASUS 28" monitor I have as well with a different HDMI cable.
 
And this is how fast a Gen3 PCIe NVME runs on this Asrock Z97 board. 50% faster than a standard SSD.

CrystalDiskMark_WD_Blsck_SN750_500GB_20221210230914.jpg
 
That's pretty gross. My WD Blue SN750 500gb on my z170 pushed 2400.
I figured it would be slow, I think it said Gen 2, 2 lanes, but thought it would be at least 1GB/s.
I am not worried about it, but I do want to figure out this HDMI thing as I don't want the fans always running when the system is off, I guess I could just get it it's own powerstrip.
Going to try DP and see what happens.

Using DP, the fans turn off with the PC, so I'll be using DP with this PC now.
 
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