Is my GPU IC faulty ?

[debi]

Hello guys,

A friend gave me a GPU Radeon Sapphire Pulse RX580 8gb pretended to be dead. No power at all. I thought it could be a good idea witha bit of luck to fix this board regarding to the amount of videos related to GPU repairs saying it's mostly dead mosfet in this case .. I have a Lab PSU and my multimeter.. After few readings, yes i don't know where im going because the problem is nothing like the repairs video show. In my case, the 2 12V fuses, close to the 8 pins connectors, have blown but i don't find short to ground after this broken fuses...
No short on the 3v or 5v rail etheir...

So i tried to inject small voltage on the 12V rail but no amp is taken at all....

I tried to find a short obviously some caps beep some of them on the GPU ic itself but i heard its because of low resistance caps in some area..

I also found a short between VSS and VDD pins of a NCP81022 chip on the right end side of the board close to the mosfets line..

If components are in parallel i understand it can be a pain to find the problem but in my case, plenty of them are beeping around the GPU chip itself... 

So i would like to know if there is a way to check if the GPU IC itself is dead and it's game over. I heard if you feed voltage on the 12v rail and you have the exact same voltage that goes to the GPU ic, it means it's game over.. but i don't know where to check.

Thank you for your help. May be im wasting my time with this board but as we say, live and learn.

Cheers
Geeom

[daisizhou]

There are still many differences between actual maintenance and video tutorials.
Do you have a heat gun and BGA soldering machine?
If not, you will have a hard time disassembling the GPU chip

[Rasz]

how do you have no shorts and simultaneously short on NCP81022 supply?

[debi]

Hello i do have a short between VDD and VSS pin from the NCP81022, i thought it could be not normal.

I checked the 4 mosfet on the right side, they are no shorted.

I join a picture to my reply with colored dots to give more infos about the board : first of all, only the fuses on the right top part are blown. I have approx 30 OHM impedance on the yellow dots linked to coils. Fall to 1 ohm on the coils (red dots) close to the mosfets. Then 0,1 ohm on the left of the CMS caps (light blue dots). 22 OHM on the blue dots coil bottom left.

The main thing is i thought i could try to inject low voltage with my psu, right after the blown fuses but he doesn't take any amps, i don't know why.

update :
Resistance from 12v circuit (after blown fuses) and ground is 3,5KOhm..

Ground to each VRM Coil is 900mOhm.

On the 3 bottom Mosfet, i can find the same voltage in the Vin and in the Phase output.. when i send voltage from my lab psu but no current drawn.
What i can see also is Voltage coming to the Vin are leaving the phase pin from the mosfet so it should be going to the core, if i refer to the datasheet but i don't find this voltage on the coil close to each mosfet...
On the upper mosfet (same column), the voltage at the Vin is approx 300mV when i send 1V. Don't know if it helps.

I also found that the NCP81022 (dual output 4 phase) has his VSS and VDD pins shorted together but not VCC.. don't know if it helps.

The mosfet from VRM core are SIC632. Diode mode on both way between Phase and Pground does not show potential on the multimeter but straight 0 on th multimeter but if i refer to the datasheet, it should be a diode blocking in on way.. i might be pointing something not wrong, because the same thing happen to the 4 mosfet. Still digging and watching video to learn.

I would love to find a way to know if the CPU from the GPU is dead.