this post was submitted on 13 Jun 2023
55 points (100.0% liked)

Technology

37716 readers
828 users here now

A nice place to discuss rumors, happenings, innovations, and challenges in the technology sphere. We also welcome discussions on the intersections of technology and society. If it’s technological news or discussion of technology, it probably belongs here.

Remember the overriding ethos on Beehaw: Be(e) Nice. Each user you encounter here is a person, and should be treated with kindness (even if they’re wrong, or use a Linux distro you don’t like). Personal attacks will not be tolerated.

Subcommunities on Beehaw:

This community's icon was made by Aaron Schneider, under the CC-BY-NC-SA 4.0 license.

founded 2 years ago
MODERATORS
alyaza@beehaw.org
TheRtRevKaiser@beehaw.org
gyrfalcon@beehaw.org
rs5th@beehaw.org
Los@beehaw.org
coldredlight@beehaw.org
SemioticStandard@beehaw.org
TheRtRevKaiser@kbin.social
remington@beehaw.org
55
WTF? This computer's CPU fan is powered on by only a HDMI monitor (streamable.com)
submitted 1 year ago by JustARegularNerd@aussie.zone to c/technology@beehaw.org
25 comments fedilink hide all child comments
 

I actually intended to post this to Reddit but I thought I would contribute content to here instead to get the ball rolling here and do my part.

Anyway, this is a Windows XP-era machine I have at work for testing, and I had just this monitor plugged into it and saw the CPU fan trying to spin. I spun it a bit myself and it just kept going. I disconnected the HDMI cable and it stopped.

The monitor is actually DisplayPort, with a passive adapter to HDMI which then goes to the HDMI cable connected to this PC. The GPU is just PCI-E. The computer has some old ~2007 AMD CPU in it. The GPU actually doesn't seem to work anyway, the PC posts normally but there's no image from either the GPU or onboard, but when putting either another GPU or no GPU, there's an image from the appropriate output.

you are viewing a single comment's thread
view the rest of the comments
[–] SevFTW@feddit.de 9 points 1 year ago (2 children)

Hahaha what the fuck 10+ years in the IT industry and a life time of playing with parts and I’ve never seen this. Does HDMI even transfer power??

[–] JustARegularNerd@aussie.zone 15 points 1 year ago (2 children)

I actually showed this to my IT lecturer and he said he hadn't seen anything like this either, but he went down the rabbit hole of HDMI specs and found that there is a small 5v 50mA power sent out from HDMI devices, presumably to detect if they're connected to something or not.

Somehow, that power must be running through the GPU, through the PCI-E slot, fuck knows where next, to the CPU fan header..

[–] Stumblinbear@pawb.social 5 points 1 year ago (1 children)

If you restart the system without the HDMI attached does the fan still not turn on? Technically it could be an obscure software issue 🤔

[–] Hexarei@beehaw.org 0 points 1 year ago (1 children)

I think that sounds logical apart from the system not being powered on at all lol

[–] UsualMap@fedia.io 2 points 1 year ago (2 children)

Only 50mA though? Is that enough to drive a fan?

I mean, it certainly seems plausible but that must be a hilariously badly designed motherboard, with also a surprisingly efficient route from the HDMI port to the CPU fan header?

[–] qtj@feddit.de 1 points 1 year ago* (last edited 1 year ago)

I think The 50mA is only the maximum current a device is allowed to draw. I found a documant from texas instrument that devices may deliver up to 0.5 A in a short circuit condition. So it could deliver more than 50mA.

[–] JustARegularNerd@aussie.zone 1 points 1 year ago

It wasn't actually enough to completely drive the fan, I had initially noticed the fan "twitching" and it was only when I had spun it myself physically, that the fan kept spinning constantly until I either unplugged the cable or I physically stopped the fan.

[–] NightmareQueenJune@beehaw.org 5 points 1 year ago

Most HDMI switches (even the ones with remotes) don't need external power so I always assumed that there must be some power spec.