Question PC Won't power on with cpu power cable in

Feb 27, 2020
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Hi,

I am new to toms hardware.

I am currently building a new pc (second time in 10 years) and am having issues powering up the sytem and would be greatful for anyones advice or experiences.

I have removed all non-essential components to search for the fault and have narrowed it down to the cpu power cable. When the CPU power cable is in the power supply will click for a split second but nothing more. I have tried reseating the CPU to no avail and checked there are no bent pins. I have checked the 8 pin cable and it's definatly marked for the CPU. I even tried powering on with the CPU not seated at all and it actually powered on but this resulting in the 8 pin connector lightly smoking (could this really be expected) and I quickly turned off and there seems to be no damage apart from grey marks on the side of the 8 pin connector (not the pins).

All this leads me to believe it's the 8 pin CPU cable (I may have squashed with case when laying on floor) and so will need a new PSU but wanted to get peoples thoughts on this as it could infact be the MB or CPU. The testing was all done with the motherboard on the box it came so that rules out the shorting issue.

My thinking atm is:
buy new PSU
if no luck get a cheap AM4 cpu to test
if still no luck test with new motherboard and hope only one component is at fault

FYI specs are:
CPU: AMD RYZEN 3800X
GPU: GTX 2070 Super
RAM: 8GB DDR4
MB: MSI X570-A-PRO
PSU: Corsair TX750M
 
Feb 27, 2020
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Can you describe the connector you used? Was it 8-pins, 6-pins with 2 additional pins that come off, or 8 pins split into two 4-pin sections?
It is an 8 pin connector that has a clip like the 24 pin MB one. It doesn't seem to split which I find rather strange but it is directly attached to the Semi Modular PSU and is labelled CPU. The MB also has a 4 pin port for CPU power 2 but I gather this is only neccessary for extreme overclocking.
 

DSzymborski

Champion
Moderator
It is an 8 pin connector that has a clip like the 24 pin MB one. It doesn't seem to split which I find rather strange but it is directly attached to the Semi Modular PSU and is labelled CPU. The MB also has a 4 pin port for CPU power 2 but I gather this is only neccessary for extreme overclocking.
Just making sure; you wouldn't believe the cables people stuff in the wrong place, even in a semi-modular PSU like this.

I'd RMA the PSU first and failing that, the GPU. Smoke is a pretty alarming thing to see, especially when nothing's connected wrong.
 
Feb 27, 2020
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Just making sure; you wouldn't believe the cables people stuff in the wrong place, even in a semi-modular PSU like this.

I'd RMA the PSU first and failing that, the GPU. Smoke is a pretty alarming thing to see, especially when nothing's connected wrong.
OK here is an image of the 8 pin connector. https://ibb.co/KhS2WM2

I think I'll give a new PSU a try and see how it goes. I guess you mean the CPU not GPU? I am tesing with only the CPU component connected to the motherboard.
 
Feb 27, 2020
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UPDATE:

So I tried a different PSU and results are the same so that isn't the issue.

I also tried reseating the CPU once again and while doing so I noticed that small amounts of the stock Ryzen heatsink pre-applied thermal paste has leaked onto the motherboard and CPU pins (see pictures). My question is could this cause damage to the MB or fry the CPU?

I am going to take the Motherboard and CPU to a local PC shop to see if they can test with different setups and perhaps they can clean the thermal paste. In this case how likely is it that I would succeed in a RMA claim?

https://ibb.co/CHZCrvQ
https://ibb.co/3mWStPj
 
Feb 27, 2020
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Is this a used motherboard? There are smears and dust and what might even be crumbs all over the place.
No it is new, the smears are where I have tried to clean the thermal paste and there are very tiny silver particles which seems to look worse with flash.

I noticed a chip near the the 8 pin connecter (picture below) that has a abnormal shaped black dot along with blue and gold dot sickers. Could it be a burnt out Voltage Regulator? Apologies for so many questions just curious as to what the issue might be.

https://ibb.co/sbSc8gR
 

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