Question PSU doesnt start up with CPU 12v and SATA cables plugged in

Jan 10, 2022
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Hi All,

I recently decided to upgrade my PC case, so after ordering one and installing my hardware into it, the power supply unit will now only turn on if it is just connected via the 20 pin motherboard connector and the 8 pin PCIe connector. The motherboard lights up and fans spin, but obviously I get no video output due to the CPU not being powered. If the CPU power cable and / or the SATA cable is plugged in, the PSU will not start at all. I have tried a new motherboard and other PSUs that I have borrowed from friends that I know work, i have also tried another CPU that was working, and another GPU, still to no avail. I have checked the PSU with a multimeter, both the 20 pin cable and 8 pin CPU cable, all voltages are perfect. I have also tried resetting the CMOS, still to no avail.

Strangely, after attempting to hook up the motherboard to the PSU outside of the case and on a non-conductive surface, it doesn't turn on at all.


The motherboards I have tried are;

MSI A320M-A PRO and Gigabyte H310M

Both processors are Ryzen 5s

PSUs are a corsair 550w and an EVGA 750GQ

GPUs are AMD 550RX 8GB nd Nvidea 1660 6gb


After putting everything back into the old case the problem still persists, I have even tried swapping motherboards and CPU combinations, still getting the same.

Any help at all would be greatly appreciated, this is driving me around the bend
 
Jan 10, 2022
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I know, it's when the cpu 4+4 cable is plugged in that the PSU or motherboard won't start up. The 8 pin PCIe is plugged into the GPU
 

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