Sapphire Nitro+ RX580 8GB GPU 12V short

[Swell61]

Hi

I picked up a faulty Sapphire Nitro+ RX580 8GB. It was pretty clean, expect from what looked like residue around the thermal pad between the rear of the board and backplate for helping to cool the memory, so I am guessing it had some liquid spilled on it at some point. All I was told is "the screen went black when playing a game".

The 12V external power appears to have a short. The two fuses have blown (circled in red on the image) and I am measuring low resistance (1.6 Ohms) on the output of the fuses to ground. When I inject power at the output of the fuses, it sucks 5A at 1.3V (my supply only goes up to 5A) and I can feel the GPU gradually getting warmer. I can't feel any other parts of the board heat up, and there is no noticeable evaporation of IPA when I pour it on. The output of the inductors (marked in yellow on the image) is 785mV.

I'm not sure what to try next, or if the GPU is already fubar. It was free but I'd rather not see it scrapped if it can be fixed.

Any help would be appreciated.

[Twiesel]

As the DRMOS are connected to the ground plane by a massive pad, the PCB sucks away all the heat.

I would suggest lifting the inductors one by one to disconnect the GPU from the VRM. Measure the resistance of 12V to GND after each removed inductor. Then you know which DRMOS is at fault.

If the issue persists, remove the coils/step down converters of the other rails as those also connect 12V to the GPU.

[Swell61]

Ah that makes sense. Thanks for your suggestion. I found https://repair.wiki/w/Short_on_12V_o...0)_GPUs_Repair which suggests connecting ground of the PSU to Vcore to find a faulty DRMOS so I will probably try that and if I still can't find the bad one I will start lifting the inductors.

If I do find a faulty DRMOS and I remove it, is it safe to replace the fuses and attempt to power it on in a system (assuming there is nothing else wrong with it) or do all DRMOSs need to be present before attempting to power on?

[Twiesel]

If I do find a faulty DRMOS and I remove it, is it safe to replace the fuses and attempt to power it on in a system (assuming there is nothing else wrong with it) or do all DRMOSs need to be present before attempting to power on?

It either works or does not, depending on the phase controller. But it wont break anything.

If it works, you should test the card with a short stress test in different scenarios. The GPU core still could have got fried and may crash under certain loads.

[noname2024]

CHECK MSFET.

[piernov]

No, do *NOT* run a stress test with a missing phase. They are there for a reason, and if one is burnt already you can only imagine what will happen if you overload the others…
Checking if it does output video in BIOS should be ok though.

[Swell61]

I found two faulty DRMOSs, removed them, and now the card powers up and displays an image (I pulled power after seeing the POST screen). I have replacements in the mail. While removing them, I also unknowingly removed one cap above each DRMOS. They go between VIN on the DRMOS and ground. Other than removing one from another DRMOS and measuring it, is there a way to tell the value of the cap that needs replacing? The application diagram in the DRMOS datasheet (FDMF3035) shows Cvin but I can't see a suggest value in the document.

[ktmmotocross]

I found two faulty DRMOSs, removed them, and now the card powers up and displays an image (I pulled power after seeing the POST screen). I have replacements in the mail. While removing them, I also unknowingly removed one cap above each DRMOS. They go between VIN on the DRMOS and ground. Other than removing one from another DRMOS and measuring it, is there a way to tell the value of the cap that needs replacing? The application diagram in the DRMOS datasheet (FDMF3035) shows Cvin but I can't see a suggest value in the document.

dont care. it is just vin capacitor. there are plenty on that rail. dont need them or just throw any suitable capacitor. it does not matter his value here