HDMI splitter powering back PC fans : weird behavior!

[VodkaCaramel]

Hey guys,

I have a very strange behavior right now with my PC and I was wondering if you can help me to figure this out. It's a pretty old Asus Essentio tower that I upgraded several times in the past 8 years (still rocking up to this day !).

I recently bought two HDMI switches so I can toggle from my PC to my work's Macbook easily with two buttons for my two screens. This specific unit.

 

While cleaning my computer with PSU cable unplugged from the wall, I realized that my front fan was still spinning and blue LED turned on. I really thought there was some black magic going on there. After making sure it was indeed unplugged from the wall, I discovered that unplugging the HDMI cable from my GTX 1060 stopped the fan from spinning.

 

The HDMI splitters are not wall-powered. How can this happen ? Is my Macbook Pro 2018 sending some power to my USB-C to HDMI dongle, then to the HDMI splitter, back to the GTX 1060 of my PC, to the motherboard and making the fan spin ? How can this loop be possible ? Could this harm my computer (the fan is running 24 hours now).

 

Thank you

 

 

[Kisai]

9 minutes ago, VodkaCaramel said:

Hey guys,

I have a very strange behavior right now with my PC and I was wondering if you can help me to figure this out. It's a pretty old Asus Essentio tower that I upgraded several times in the past 8 years (still rocking up to this day !).

I recently bought two HDMI switches so I can toggle from my PC to my work's Macbook easily with two buttons for my two screens. This specific unit.

 

While cleaning my computer with PSU cable unplugged from the wall, I realized that my front fan was still spinning and blue LED turned on. I really thought there was some black magic going on there. After making sure it was indeed unplugged from the wall, I discovered that unplugging the HDMI cable from my GTX 1060 stopped the fan from spinning.

 

The HDMI splitters are not wall-powered. How can this happen ? Is my Macbook Pro 2018 sending some power to my USB-C to HDMI dongle, then to the HDMI splitter, back to the GTX 1060 of my PC, to the motherboard and making the fan spin ? How can this loop be possible ? Could this harm my computer (the fan is running 24 hours now).

 

Thank you

 

 

This seems unusual, but it might simply be the HDMI switch is powered but is leaking current. The GPU might be passing this directly to the motherboard's 12V bus, or the GPU might be passing it to the 6-pin/8-pin PSU connector, which would be connected internally to all the 12V rails.

 

If they are not wall powered (eg they are passive), then it's the power from the TV or monitor CEC doing it. 

 

https://e2e.ti.com/support/interface/f/138/t/535155?TS3DV642-HDMI-switch-HPD-voltage-leakage-issue

Quote

my customer adopted TS3DV642 for HDMI, DVI switch on their mini PC system, they got a question that when their system is power off, and they connect the HDMI panel cable to their system HDMI port(connector), in this case they observed that there is 5V voltage on the HPD signal of the TS3DV642 device, since this has power dissipation during the system power off stage, so they want to know how to avoid this 5V voltage leakage on system power off stage?

...

Yes, to my understanding this is the proper operation of HDMI.  The HDMI source uses this 5V signal to know that a HDMI sink has been connected.