Baffled - Bizarre new PSU issues! Help!

Deadbolt91

Hello folks,

I took a search through the FAQs and forums and didn't find anything the same as the issue I am having so please excuse me if I did miss something. That said, I would very much appreciate any help you might be able to offer!

I have had a custom built PC for a few years now and have upgraded it here and there as necessary, but never had any issues. I recently got a new Corsair RM 850X PSU to replace my older EVGA 650W PSU as I want to upgrade my GPU. Now I'm seeing the weirdest behaviour after installing it.

I replaced all the old PSU cables with the ones that came with the new Corsair PSU, but now it won't boot. I'm getting power to the mobo as the RGB lights come on, but when I try to boot, the fans spin for a second and then immediately stop.

To troubleshoot, I tried a combination of swapping around some cables and putting the old PSU back in and this is what I found:

650w psu:
Powers mobo with old cable only
Boots with old cpu cable without issue
Doesn't boot with either new cpu cable

850w psu:
Powers mobo with new power cable only
Doesn't boot with any cpu cable

I'm pretty certain all other components are working since it boots with the 650w PSU. Could it be that the new PSU has an issue with both of the CPU modular slots on it?? If not, I'm utterly baffled!

Some more info below if it helps:
Mobo: Asus ROG Strix X570-F
CPU: Ryzen 3700X
New PSU: Corsair RM 850X
RAM: 2 x 8GB HyperX Fury

Has anyone seen anything like this before? Would really appreciate any advice!

Sincerely,
Losing my mind.

unkel

You should strictly only use the cables that came with the respective PSUs

Also, when you made a mistake with above and the rig is no longer starting up, you can usually get it back going again by switching off the on/off switch on the PSU, then pressing the power button on the PC for 10s, then taking out the connectors between motherboard and PSU, doing above again pressing the power button on the PC for 10s, then plugging back in the connectors between motherboard and PSU and then powering up as normal with the power button

spix

I've read alot obout DOA corsair power supplies. I think your new one is just broken.
Just make sure the cables are pushed in fully, some can be more difficult.
It shouldn't be expected to work with cables from other psu.

JoyPad

I recently replace my PSU, before upgrading the GPU.
I knew that I had to replace all the cables, that was not an issue.
Powering up with the new PSU did not work. The motherboard would light up, but nothing else would happen when pushing the power button.

What fixed it was a CMOS reset. No clue why, but I tried that and then the new PSU would work.

unkel

Yeah sometimes the mobo and the PSU just don't want to shake hands. My solution above should do the trick in most cases. Good call to try a CMOS reset next if this doesn't work.

spix

JoyPad wrote: »

I recently replace my PSU, before upgrading the GPU.
I knew that I had to replace all the cables, that was not an issue.
Powering up with the new PSU did not work. The motherboard would light up, but nothing else would happen when pushing the power button.

What fixed it was a CMOS reset. No clue why, but I tried that and then the new PSU would work.

I was going to suggest the good ol cmos reset but couldn't imagine why that would help and I've also switched psu's several times before without needing to reset. Could be some kind of safety feature on the motherboard.

spix

Replacement PSU won’t boot (CMOS clearing)

If the PC does not boot up after the power supply has just been replaced, Seasonic recommends clearing the CMOS memory of the motherboard to reset the motherboard to its factory default state in order to clear the settings related to the previous power supply.

Listed below are a few common methods to clear the CMOS in this situation; however, Seasonic suggests you consult motherboard’s user manual to reset the CMOS.
Reseat the CMOS battery

Unplug the power supply from the AC mains.
Locate the CMOS battery, usually a button cell, aka, watch battery, on your motherboard.
Remove, then reconnect the battery.


Use a clear CMOS jumper

Unplug the power supply from the AC mains.
Locate the jumper on the motherboard; it is often labelled CLEAR CMOS.
Follow the instructions on the motherboard’s user manual to short the pins using the plastic jumper.
Plug in the AC power, then turn the computer ON to make sure the BIOS has been reset.
Turn OFF the computer, and set the jumper back to its original position.

Deadbolt91

Thanks so much for your replies amd advice folks, I knew it was 'good practice' to use the cables that come with a new PSU, but never realised it was mandatory. I finally managed to get it working with your help!

I removed the mobo from the case and connected only the CPU and mobo power cables to the new PSU, and lo and behold it booted to BIOS. Then I put it back in the case and added each component one by one with a test boot each time to try and find the offender, but I didnt have any more issues after that. The only thing I can think of is that I had previously still been using the PCIe power cable for my flash drive and hdd, and replaced that today with the new cable after putting the mobo back in the case. Can a PSU really tell if its not using its own branded PCIe cable and halt the boot? Other than that, maybe some sort of grounding or short in the case I guess but I have no idea where.

Thanks so much for all of the help, I really appreciate it! Can finally play flight sim now 😂

unkel

Yep even a lowly PCI-e cable from a different PSU can stop the whole PC from booting. Been there, done that (many times)

Glad you got it working!

TheValeyard

Congrats its working. I actually think you're lucky you didn't fry your hard drives!


(speaking from experience here lol)

unkel

Or a GPU. Hard drives are cheap, GPUs are not

TheValeyard

unkel wrote: »

Or a GPU. Hard drives are cheap, GPUs are not

And rare!