Hi all,
 
I have just finished building a new PC and am having a strange issue with my 1200 P2 (around 4 years old).  As soon as I flip the power switch on the PSU the PSU fan starts spinning, once i turn the PC on the fan goes off (Eco mode is on, if i turn it off the fan spins) and seemingly operates normally.  When i shut down the PC from windows the PSU fan will stay spinning.  It will only stop if I flick the switch on the PSU to off.  I have disconnected the 24 pin from the motherboard and used the jumper and everything operated normally.  I was using cable extensions, though i tried with no extension and the same behaviour occured.  The PC appears to be running fine, no strange behaviour)
 
I do have another PSU though due to the cabling set-up it is a major effort to unplug the P2.  Am i able to leave all the cables except the 24 pin plugged into the P2 and components (no power going into the P2) and just plug the 24 pin cable from my spare PSU into the motherboard to see if it shows the same behaviour when i flick the PSU switch or would this damage things?
 
Components are : 3900x, Gigabyte master x570, 2080ti, 32gb ram, 2 nvme drives, 1 hdd, 2 D5 pumps, Aquaero 6 lt, Quadro.
 
Hope the post makes sense.

the First PSU would need a jumper to start .... as only the second PSU would see the "start button signal" from your case
 
Do you have other self-powered devices connected to the MB ? (printer, USB hub ...)
Test will all devices except KB, mouse & monitor disconnected

kwomo
Am i able to leave all the cables except the 24 pin plugged into the P2 and components (no power going into the P2) and just plug the 24 pin cable from my spare PSU into the motherboard to see if it shows the same behaviour when i flick the PSU switch or would this damage things?

 
That's fine..What is your spare PSU, by the way?
 

Thanks for the reply.  I do have a sata powered USB hub/splitter connected to the motherboard.  I'll disconnect everything and see what happens.

Thanks for your reply, i'll give that a try later today and see what happens.  It's a Coolermaster MWE 550w gold.

Just to be clear, don't use ANY cables from the EVGA unit with the Coolemaster, and vice-versa..But you probably already knew that. 

bob16314
Just to be clear, don't use ANY cables from the EVGA unit with the Coolemaster, and vice-versa..But you probably already knew that. 

Yeah I definitely won't be doing that.  Thanks for the reminder though. 

Just an update.  Doesn't look like it's a PSU problem.  I disconnected everything plugged into the motherboard except the 24 pin and the PSU fan still started spinning as soon as I flipped the PSU switch to the on position.  I did the same test using my other PSU and the fan started spinning as soon as I flipped the switch also.  I guess that means it's motherboard related...now is it something worth worrying about, seem everything looks to be running fine.  Thanks for your help.
 

Well, let's not be too hasty in condemning any hardware yet without trying a few things first.

1. Make sure the Mobo BIOS is up-to-date with the latest from your mobo page at Gigabyte, I see there's 5 updates for an X570 Aorus Master since initial release.

2. Enable ErP Mode in the BIOS -> Settings section.

3. Contact Gigabyte Support and see what they say (but my crystal ball tells me they'll say the PSUs you tried are bad).

Keep us posted after trying bob16314 suggestions