Gigabyte Brix Pro 4770R motherboard shorted!

[gamalot]

This mini PC is powered by a common laptop style 20V/7A DC power adaptor. When I connect it to the mains, the power adaptor will enter the protection state and cut off it's output to PC.

I measured the input resistance of the PC's power in jack, which was determined to be shorted. I also measured all the MLCCs on the motherboard, between 20V rail and ground, all their resistance values are less than 100 milliohms.

Any suggestions? MLCCs, MOSFETs, or maybe DC-DC converters? 

[Mechatrommer]

heat gun? starting from input jack?

[wraper]

Look for TVS diode connected between 20V rail and GND.

[gamalot]

heat gun? starting from input jack?

It seems like the input jack is OK.

[gamalot]

Look for TVS diode connected between 20V rail and GND.

I didn't find anything looks like TVS. 

[gamalot]

Damn it! I can't even get a capacitor off the motherboard, it must be red glue !!! 

[wraper]

Damn it! I can't even get a capacitor off the motherboard, it must be red glue !!! 

Very unlikely. Not used motherboards. Post photos of the PCB.
TVS diode should look like this:

[gamalot]

Damn it! I can't even get a capacitor off the motherboard, it must be red glue !!! 

Very unlikely. Not used motherboards. Post photos of the PCB.
TVS diode should look like this:

I know TVSs look like diodes, actually I have even checked all TO23 components.

Pictures attached, sorry maybe they are not clear enough. 

[wraper]

Damn it! I can't even get a capacitor off the motherboard, it must be red glue !!! 

Do you mean black capacitor nearby connector? If it's sitting on 20V rail, quite possible it has gone short.

[gamalot]

Damn it! I can't even get a capacitor off the motherboard, it must be red glue !!! 

Do you mean black capacitor nearby connector? It's quite possible it has gone short.

No, I mean those size 0805 MLCC capacitors. Big black components are 330uf tantalum capacitors, maybe only rated at 2V, I guess.

[Mechatrommer]

heat gun? starting from input jack?

It seems like the input jack is OK.

next? black ic and diode near it look interesting. the 2nd left diode? in the group of 4 also looks not so good.

[gamalot]

heat gun? starting from input jack?

It seems like the input jack is OK.

next? black ic and diode near it look interesting. the 2nd left diode? in the group of 4 also looks not so good.

Those things look like diode are actually low voltage tantalum capacitors.

[gamalot]

Finally I decided to add 5A current to the motherboard, after a few seconds a DC-DC chip becomes very hot! 

[Rasz]

Damn it! I can't even get a capacitor off the motherboard, it must be red glue !!! 

8 or more layer pcb, hotair + preheater or you risk deforming/ripping pads off
take off TPS51363 and measure again
I would also measure all the PL inductors to ground

[gamalot]

Damn it! I can't even get a capacitor off the motherboard, it must be red glue !!! 

8 or more layer pcb, hotair + preheater or you risk deforming/ripping pads off
take off TPS51363 and measure again
I would also measure all the PL inductors to ground

The trouble I am having now is that I don't have a preheater. 

[Mechatrommer]

Finally I decided to add 5A current to the motherboard, after a few seconds a DC-DC chip becomes very hot! 

check downstream for the short. or disconnect load if possible. and also check the dc dc if its "pwm"ing.. tool needed... oscilloscope.. thats the reason i bought seek thermal