Question 8 pin ATX 12V Connector on AS Rock 970 Pro 3 motherboard tripping PSU

Mar 25, 2020
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Hi, I have a gaming PC running a AS Rock 970 Pro3 motherboard. This has stopped working - when the PC is powered up, the LEDs flash once for half a second and the PSU switches off therafter.

I have replaced the PSU with a new unit, and the result is the same.

During faultfinding, the tripping disappears when the 8 pin ATX 12V Connector on the motherboard is not plugged in. This connector apparently supplies more power to the CPU according to the manual.

We have also unplugged the cooling fans on the ECU cooler (Cooler Master) with no change - the fans do run if the PC powers up without the 8 pin connector plugged in.

A concern that I have is that we can damage the motherboard if we switch on and off while testing with this plug not plugged in. We have not yet removed and re-seated the CPU, and not sure if this would help?

Any suggestions for faultfinding welcomed.
 
Mar 25, 2020
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I purchased a new reputable brand PSU and it behaves exactly like the old one did, so this would rule out PSU?

In terms of other tests that I can perform on the motherboard, is there something I can do if I do not have a spare ECU or motherboard to swop out with, apart from visual inspection?
 
Mar 26, 2020
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Wow, I just registered here to start a thread because I have the EXACT same problem after I found absolutely nothing similar on the internet and then I see this thread, kinda strange isn't it?
Anyway, my thinking was that the old PSU was indeed faulty and a power surge destroyed something on the mainboard, hence why it won't work even with a new PSU. Can you remove your CPU and see if the problem persists?
 
Mar 25, 2020
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I removed the CPU yesterday and put it back in afterwards, no change. Are you suggesting removing it and trying the PC without the CPU plugged in to see if the power supply still trips?
 
Mar 26, 2020
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I removed the CPU yesterday and put it back in afterwards, no change. Are you suggesting removing it and trying the PC without the CPU plugged in to see if the power supply still trips?
Exactly. If nothing else at least you'll know whether the CPU itself is toast or only the board, if its a PSU failure as I suspect. Could still have killed both I guess. But the problem persisted for me even without the CPU, thought it would be interesting to know if its the same for you

Edit: Just to make sure there's no misunderstanding, I meant removing the CPU but leaving the 12V CPU connector plugged in and trying it this way. Result was all the same for me.
 

bignastyid

Titan
Moderator
Exactly. If nothing else at least you'll know whether the CPU itself is toast or only the board, if its a PSU failure as I suspect. Could still have killed both I guess. But the problem persisted for me even without the CPU, thought it would be interesting to know if its the same for you
Trying the system with no cpu isn't going to do anything as the cpu is required to post. OP would need a known good cpu or motherboard to know if one or the other is failing.
 
Mar 26, 2020
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Trying the system with no cpu isn't going to do anything as the cpu is required to post. OP would need a known good cpu or motherboard to know if one or the other is failing.
Sure it won't POST without a CPU, but if the problem remains the same without the CPU installed it would suggest the board is definitely faulty, wouldn't it? Of course you can't be sure about the CPU.
 

bignastyid

Titan
Moderator
Sure it won't POST without a CPU, but if the problem remains the same without the CPU installed it would suggest the board is definitely faulty, wouldn't it? Of course you can't be sure about the CPU.
No. Without a cpu some boards won't turn on at all, some will start to power on and just shutdown, some power on and off in a loop, some power up(not post of coarse) but only power fans and lights and some will display a post code and or beep code for no cpu installed. So just trying without a cpu is usually just a waste of time as it doesn't tell you much if anything. Same can be said of removing the cpu power connector.
 
Mar 26, 2020
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Same can be said of removing the cpu power connector.
Sorry I don't mean to be rude, but why do you say removing the CPU power connector is a waste of time when we already figured out it seems to be part of the problem? OP said the problem of the PSU tripping and turning off power disappeared when he disconnected 12V power, and it's exactly the same for me as I have the same problem, just with a different board. My suggestion to remove the CPU was purely an idea to see if the board itself trips the overload protection of the PSU or if theres maybe a short in the CPU itself.

Edit: I see your point about how you can't be sure what the board will do without a CPU, but my point is if the PSU cuts power instantly even without a CPU installed, it doesn't really matter how the board reacts to not having a CPU installed because there seems to be a dead component or short directly on the board. And if the VRM was killed by the PSU (or just died by itself as you suggested earlier) I wouldn't recommend leaving the CPU in there anyway, maybe it survived but you might still kill it afterwards.
 
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Mar 25, 2020
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I will unplug my CPU and report back, even though as suggested, it might not prove much if the PSU still trips immediately. However, if the PSU does not trip immediately, it would point towards the CPU in my uneducated opinion?
 
Mar 26, 2020
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Removing the 8 pin and it staying on proves nothing. It would display the same thing if the cpu and 8-pin was removed. It does not indicate which component has failed and is a waste of time.
Still don't get your point, if removing the 8 pin fixes the problem of the PSU safety tripping (regardless of CPU being installed or not) it does prove there's something wrong with the VRMs??

Anyway, whats your suggestion then?
 
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Mar 25, 2020
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I have removed the ECU - still trips PSU.

Then went through a few things:
Removed RAM chipsets, cleaned contacts using an eraser, swopped them around to different slots, used only one at a time (I have two in total) - no effect.
Also unpugged everything from the motherboard except for CPU with it's fans and the boot-up drive - no effect.

Any other suggestions?
 

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