Question PC New Build Won't Boot when 8-pin connector is plugged

[misha0001]

Just finished a new build last night:
ASRock B450 Steel Legend MB, AMD Ryzen 3 2200G, no additional GPU
Symptoms: Computer powers up, but does not get to post, no beeps.
Runs for about 15 seconds, all fans, lights, all connections seem to run normally, then it shuts down, restarts itself and continues cycling.

Timeline of troubleshooting:
- Cleared CMOS and also reseated the battery
- Unplugged everything one by one, re-testing. Finally Isolated the problem down to the 8 pin power connector. When not plugged the computer does not shut down.
- Tested the PSU with a DMM, and then also with another board, all good.
- Took the MB out of the case, same symptoms , so not shorting
- Checked the connection between the heat sink and the CPU. Thermal paste is not spread very evenly but there seems to be enough of it. Did not reapply. Otherwise it all seems tight...

Is it possible that it shuts down just because of the heat sink, thermal paste? So quickly?
I can return the CPU and/or the MB, which one would you try first? Or any other testing suggestions?

 

[rgd1101]

check for bend pin on the cpu?

 

[misha0001]

Just managed to put another CPU in, same problem...
At this point it seems like it's gotta be the MB, but... I will wait for any other suggestions for another day before I RMA it (it's "replacement only" at Newegg, and I will lose the rebate deal )

 

[misha0001]

Okie, I am going crazy here...
Now I have two identical Steel Legend motherboards, two Ryzen 3 processors (2200g/3200g), and two DDR 4 DIMMs (Geil and G.Skill). Also two working PSUs. In all combinations, both MBs shut down after about 20 sec, without POSTing.
They cannot both be defective, and all other components have been tested. So, I suspect I am not doing something right.
I've built quite a few computers before, and this is the first time I am running into such a problem...
I don't want to just return everything to Amazon/Newegg and tell the world that the boards are crappy... there must be something else going on...
ASRock technical help has been limited to "Have you checked our FAQs?"
Any suggestion/advice would be warmly appreciated

 

[rgd1101]

make and model of the ram and psu?

 

[misha0001]

make and model of the ram and psu?

AMD Ryzen 3 2200G
AMD Ryzen 3 3200G

GSkill Aegis 16 GB DDR4 2666,
GeIL EVO POTENZA 16GB DDR4 3000
Plugged into A2 slot, as suggested, one at a time
CPUs checked for bent pins...

PSUs: Thermaltake Toughpower Gold 750W
EVGA 400W

 

[rgd1101]

you tested both 2200g and 3200g?

 

[misha0001]

you tested both 2200g and 3200g?

Yep... Tested both on both MBs
What's strange is that it takes more than 20 sec to shut down (and restart) and during this time it does not seem that anything is happening except leds and fans working... no beeps, no signs that the board is trying to POST. What could be taking so long?

 

[rgd1101]

test with 1 stick of ram
rma the motherboard?

 

[misha0001]

test with 1 stick of ram
rma the motherboard?

I tested with 1 stick of RAM
The MB is "replacement only" , so i got another one... and it's exactly the same issue. Up until that point, I was sure that I determined the MB to be the cause... But what's the likelihood of two boards having the exact same problem? I wish ASRock people were more helpful... And at the same time wondering how come this was not a more common problem