What could be causing my PCU to trip my PSU?

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Isaac_7

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Oct 29, 2015
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Hi,

I'm having some trouble with my desktop computer where the PSU clicks and turns off as soon as i try to power it up. I systematically went through all the cables and found that when the 4pin ATAX +12V cable is plugged into the motherboard the PSU trips. At first I assumed it was a thermal trigger because the clip at the bottom of the CPU mounting was broken but after repairing it, it still wont turn on. Also the PSU isn't broken it powers up fine with the paperclip test and as long as theres no power going to the CPU. So if its not the PSU and its not a thermal trigger, what else could be tripping it?

thanks in advance for any help anyone can give me!
 
Solution
InvalidError
If you have a multimeter, try measuring resistance or diode voltage between one of the 12V pins and one of the GND pins. (PSU off and ATX/ATX12V connectors disconnected) If you get less than 10 ohms (after waiting for a few seconds for capacitors to charge) or 0.5V of diode drop, something on the ATX12V rail went short.
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maxwellmelon

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Oct 2, 2013
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is this an intel or amd cpu?
if it is intel did you have to install the fan cooler bracket?

did you check the cpu socket/ cpu for bent pins?
if intel and you installed fan cooler bracket to motherboard you might want to undo it and make sure that you didn't damage any traces by the 4 holes.
 
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InvalidError

InvalidError

Titan
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May 18, 2007
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The paperclip test tells you very little beyond whether the PSU is completely dead or not. You could feed 12V AC (~30Vpp of ripple) to some fans and they would still work, albeit at less than half the power.

If the PSU shuts down when you connect the ATX12V connector, you either have a short on the motherboard (either a piece of metal shorting something out or a busted component) or a dying/dead PSU.

What's the age, brand and exact model of that PSU?
 
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Isaac_7

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Oct 29, 2015
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I think it was an AMD but I can't exactly remember but either way it was a fan cooler bracket but there was a 2 of them, a top and a bottom one. The bottom one I fixed, but the issue was occurring before I replaced the bracket. I fixed the bracket assuming that it was a thermal trigger. Or could it be a coincidence that it was the thermal trigger at first and then i damaged something fitting the bracket?
 
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Isaac_7

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The PSU is less than 8 months old (most of which the pc wasnt turned on for however), and its a Cool Master G750M 750V
 
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InvalidError

InvalidError

Titan
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With a decent quality and relatively fresh PSU, a short somewhere is the most likely problem. Remove the bracket, inspect for any visible damage and if everything looks fine, you could try simply sitting the heatsink on top of the CPU and see if you get any better luck. If the PC POSTS, then you know something got shorted out by the bracket. If you still get nothing, there may be a short on the motherboard itself.
 
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maxwellmelon

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well is it a plastic or metal the new bracket? a plastic bracket cant short anything so no issues there. a metal bracket can cause shorts if there are exposed metal traces..
 
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Isaac_7

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I think I need to clarify something, I didn't fix and replace the mountings for the pcu but rather a plastic bracket which kept the heatsink in place which was my reasoning for assuming it was a thermal trigger. I tried removing the plastic bracket and booting up but nothing changed. A little bit of power, fans move a little and then a click and it turns off.
 
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Isaac_7

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Some information I forgot to include is that after starting the pc for the first time in a number of months it did boot up perfectly fine.Then after logging in and the system was loading it suddenly shut down and that's when the problem started and I found the broken bracket.
 
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Isaac_7

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UPDATE: I just tried to boot the motherboard out of the case on a static proof surface and nothing changed. So if its not the motherboard shorting on the case, and its not a thermal trigger what can i do? Is the motherboard broken or I'm praying for another option.
 
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InvalidError

InvalidError

Titan
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If you have a multimeter, try measuring resistance or diode voltage between one of the 12V pins and one of the GND pins. (PSU off and ATX/ATX12V connectors disconnected) If you get less than 10 ohms (after waiting for a few seconds for capacitors to charge) or 0.5V of diode drop, something on the ATX12V rail went short.
 
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