Question B460M-DS3H intel core i5 10th gen pc wont start

[zz350]

Hi

I have a problem with my computer that wont start. Issues started when running quite heavy arduino scripts
via the pc usb port. I noticed from time to time the computer slows down but a reboot or wait solves the problem
and then one day while running a script the computer freezed when I rebooted it I had a blinking power led and also I discovered later that
all my HDD drives went raw ... the ssd were fine. The power supply has to be good because it runs fine with another computer.
So jumping P+ and P- with a jumper absolutely nothing happens, PS_ON stays high. Should i help it a little bit by pulling PS_ON to ground ... or is there
a reason for that situation. I've tested every voltage input on the motherboard with an ohmeter, no short so supplying power shouldnt be a problem.
I've also tried feeding 12 volts to the cpu via a separate lab power supply, nothing, from what it seems the configuration per phase would be a 3 mosfet ...
where there is upper mosfet, lower mosfet, and a third mosfet (?) whose role seems to retain 12 volt on command
or maybe it acts as an inverter to supply the opposite dutycycle of the pair ... No dutycycle anyway on the gates
of upper and lower and the lab power supply shows about 50 mA of current. I also noticed 5V stb is being fed as power in the USB port .... is it normal ?
my understanding is that 5V stb shouldnt be used for heavy lifting its only 15 watts. which means i have a computer that turns on one of the famous usb tester but wont start.
That said for some reason the motherboard manual insists on having a beefy power supply.
Any suggestions ? I donc really know where to go from here. I was wondering what part of the system pulls
PS_ON to ground ?

Thanks

 

[zz350]

To add to the previous message the power consumption of the power supply is 10 watts,
the pch (?) gets quite hot (the heatsink with gigabyte written). But i think it's normal hence the heatsink.
For the bios all pins a part from ground are pullled high to 3.3 and that's it ...

 

[duzytv]

From what you ve written you ve already done a lot more than I could imagine and have positively answered is psu ok ?
I suggest the next one could be is mobo ok?
https://forums.tomshardware.com/threads/new-build-stand-by-led-on-motherboard-keeps-blinking.191248

 

[zz350]

Ok thanks.
Unfortunately I dont have the blinking light on the motherboard. I've actually removed everything ant the board is now directly
on the table on paper. Everything has been removed just left power to motherboard and power to cpu. Despite that no beep i plugged a speaker.
I think it could help to know exactly in details the sequence that happens once P+ and P- are touched which i cant seem to find anywhere.

 

[zz350]

Hum At this point i guess mobo replacement.

 

[duzytv]

Yes looks like the motherboard collapsed under some heavy load...
I would eavesdrop for any beeps also with any RAM just to be sure and not scrap an undamaged component.

 

[zz350]

Yes looks like the motherboard collapsed under some heavy load...
I would eavesdrop for any beeps also with any RAM just to be sure and not scrap an undamaged component.

Yup the problem is dont even have a beep, PS_ON is never pulled down, I checked with a scope the mb doesnt even try to wake up the power supply.
I am going to try the RMA solution. I think it's still under warranty.
I've done a bit of research in the meantime looking up chip references and measuring voltages and what not.
it seems a voltage regulator supposed to feed 3.3 outputs only 2.8 , it's ref value (normally 1.25) has shifted to ~ 1.75
And weirdly the power switch plus is at 2.8 volts .......... Not sure it's the only problem.