[SOLVED] Why would a MB power on, when I connect a PSU tester to the ATX cable?

[Rick_S]

I've been wrestling with an Aorus B550 master that I'm installing , and so far it seems to be winning. I've updated THE BIOS with the latest version, yet I'm still having two problems. I need explain them both as context to my question. First of all, I have the problem of all fans turning on, when I turn the power supply on. This has been discussed here. The second problem, is that sometimes the B550 won't power on at all , for no reason that I can find. Here is that link : https://hardforum.com/threads/gigabyte-x570-aorus-master-wont-power-on-temporary-solution.1993194/

Now, to my question. I found that when I plug the 24 pin ATX plug into a PSU tester, that turns the fans on as well. The 8 pin board connecter is hooked up. The ATX connection had worked, when all the fans were running, before that connection lost power. Any ideas that may help? I'm stymied. Thanks.

 

[drea.drechsler]

I've been wrestling with an Aorus B550 master that I'm installing , and so far it seems to be winning. I've updated THE BIOS with the latest version, yet I'm still having two problems. I need explain them both as context to my question. First of all, I have the problem of all fans turning on, when I turn the power supply on. This has been discussed here. The second problem, is that sometimes the B550 won't power on at all , for no reason that I can find. Here is that link : https://hardforum.com/threads/gigabyte-x570-aorus-master-wont-power-on-temporary-solution.1993194/

Now, to my question. I found that when I plug the 24 pin ATX plug into a PSU tester, that turns the fans on as well. The 8 pin board connecter is hooked up. The ATX connection had worked, when all the fans were running, before that connection lost power. Any ideas that may help? I'm stymied. Thanks.

I think it's normal for all fans to spin up briefly at power-on, part of POST.

So if I understand...the 24 pin ATX connector is attached to a PSU tester, not the motherboard, so all that's connected to the motherboard is the 8 pin CPU power on the motherboard...and what about the GPU? is it installed and the supplemental 12V power connectors still attached? any SATA drive power connectors attached to drives?

Either way...I don't think the supplemental connectors are supposed to power the motherboard, only the devices (CPU, GPU or SATA drives respectively). If right, then perhaps something has an internal short feeding +12v back to the motherboard. A schematic of the motherboard would be needed to figure out if something on the motherboard is at fault. Or perhaps something is wired in a non-standard way?

I'd disconnect devices one by one until it stops completely.

 

[Rick_S]

Thank you! The GPU had been pulled, but not the SATA or MOLEX power plugs to the PSU. Unplugging them made things. Now I can focus on them for the problems. Feedback is so important!