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VX-450W PSU fried 3 motherboards, won't start when 4Pin 12v connector is plugged in

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I'm writing about a year old VX-450w Corsair power supply which has fried one old motherboard and two new ones, and refuses to power up when the 4Pin 12v rail is plugged into a motherboard.


The first time it happened I assumed the motherboard failed of its own accord. The fans/drives all started fine when I tried switching the PC on, but the system refused to POST and I couldn't access the bios. Sometimes after hours of switching it on and off it would randomly manage to boot into Windows, only to crash hours later and refuse to POST all over again. After a few days it wouldn't boot at all.


I upgraded the motherboard and RAM and found it booted fine, so I assumed the problems were solved. I did notice the PSU seemed hotter than usual, but not enough to cause alarm. Then a week later the system suddenly lost power, and refused to switch on at all. Looking inside the case I could see that when I tried to power on the fans moved for a fraction of a second and the motherboard lights came on, but nothing else happened.


On a hunch I tried powering on without the 4-pin 12v rail plugged in, and found the fans and drives all started yet the system wouldn't POST, the same as what had happened with the old motherboard.


I RMA'd the new motherboard, figuring there was some problem with the 12V socket. I also changed the CPU and case, making sure nothing was short-circuiting the board inside the case. Again I found the new motherboard worked, except this time it only lasted 2 hours before powering off suddenly and giving the same symptoms as before.


It's been a tricky problem to diagnose, as the PSU seems to work as long as the 12v rail isn't plugged in. I tried jump-starting it with only the DVD drive connected, and it powers up fine. Yet I'm sure it's the source of my problems as I've replaced all of my core components, some multiple times, and the problem persists.


I've applied for a RMA and will mail the PSU soon, but I'm concerned that the problem won't be detected & my request for a replacement denied as the fault is difficult to replicate in testing and could take anywhere from two hours to a week to show up if my experience is anything to go by.

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