Question Can’t get mobo to post (mobo & psu ok?)

Oct 25, 2020
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I have 2 machines

One an ASUS b150m with a Corsair rm550 psu and a
ASUS z270-a with Corsair hx1200i psu

The hx1200i was RMA’d after going ‘bang’ after 2 yrs

Now the new hx1200i won’t post the z270-a. However the Corsair Rm550 PSU will post that mobo into Win10 just fine.But the hx1200i itself seems ok because it will post the b150-m just fine.

So I seem to have proved both z270-a and hx1200i work with components but not together as they did before.

I’ve tried everything I can think:

Stripped z270-A down to cpu+Ram
Reset cmos
Booted it with another psu ok
Reseated all components.
I know the ram is ok.
Plugged the hx1200i into another pc & booted to bios to check the voltage rails are stable. 12,3,5 & cpu voltage.
Tried different modular cables for PSU

Why will one psu post the board but the other won’t but the other posts another pc.

When trying to post with the hx1200i the green led power light is on when I switch the psu on. On start button (on mobo) the cpu fan spins but no beep or post.

I’m stuck and going in circles now. Any suggestions? Thinking of getting a psu tester but as I said it posted my other pc (B150-m) fine and was stable for 24hrs. Voltage in bios looked fine

I’m leaning towards a weird mobo fault (a bit in despair) because my Corsair 550 boots that machine fine.

any suggestions r appreciated. Thanks.
 
Oct 25, 2020
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Hi,

Thanks for comment.

The hx1200i came with 2 12v CPU cables (different lengths) so tried both. The 12v ATX cable for the corsair RM550x also fits the hx1200i because it is the same type of 12v ATX cable so tried swapping those (considering I was able, with that specific 12v cable on the RM550x to boot the mobo successfully)

Granted the 24 ATX cables are different at the point they plug into the PSU but I've eliminated those by proving each can successfully post another mobo so they must be working ok in themselves.

Feel like I must have missed something simple. Just can't find it.
 
Oct 25, 2020
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Found out some PSU's have a minimum power draw requirement before they will boot.

How do I add more load to the PSU in this case?

I have the Ram installed, CPU+fan and HDD. Don't think power is getting to the usb ports at the point I'm gettin to.
 
Oct 25, 2020
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Plugged in some chassis fans which did not spin when turning on the power to attempt to boot up. (the CPU fan does). Plugged in an Rx580 GPU. The Fan lights to the GPU came on but it did not spin it's fans up and self test as it would usually do on boot. Probably just means there is power to the PCI slot nothing else. The lights at least proved I have the PSU supplying more power but still no success on getting the mobo to POST. Jury's out on whether this is related to the minimum power draw on the PSU.

It's acting like the 12v ATX is just not plugged in to the mobo. I've swapped between the 4 different 4 pin modular slots on the PSU and used 2 diff cables (which successfully booted another pc).
 

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