RTX 2070 Fan not operating - 12v present at header but drops to 2V when fan connected

[tintin_sn2]

I recently purchased a second hand RTX 2070 - an OEM Acer Predator manufactured by Sapphire - not a very common model.

Upon connecting it up I noticed the fan wasn't operating resulting in the card overheating and shutting down. I checked the fan operation independently by connecting it directly to a power supply and function generator - it was working correctly with variable speed according to the square wave frequency.

I then checked the output with a multimeter/DSO and verified that the GPU was putting out both 12V at pin 2 and PWM at pin 4. However, when the fan is connected, the output on pin 2 drops to 2V. The only explanation I can think of is that the 12V power supply circuit has high resistance somewhere. There was a lot of dust and some surface corrosion around that area so that seems plausible to me.

Pic attached for reference. The fan header is the black 4-pin connector at the top, just below the white LED header.

One simple solution that I can think of would be to just wire the 12v pin on the fan directly to the nearby GPU power supply, but I am unsure if this is safe or if I should place some resistor or other component in-line? From looking at the 2080 schematic, it seems like the 12v power is just wired directly to the fan - there's only a 0 ohm resistor which doesn't appear to serve any purpose?

[прямо]

Because an 0805 fuse cost 10% more than an 0805 zero ohm resistor.

And yes you can feed the fan 12V directly from any 12V source on the GPU, such as the 12V PCIE lane, or the 12V PCIE external.

[tintin_sn2]

Unfortunately things have taken a turn for the worse. I soldered a pin to the 12V supply from the PSU and hooked up the fan. It worked at first. It powered on and the fans were working. I did a GPU stress test to see if the RPM would increase with temperature, and it did until it hit around 50% speed, then there was a loud pop. Looks like I blew some of the capacitors at the base of the 12V rail. Either the didn't like the voltage drop or there was a short from me failing to clean the flux from the board after soldering:



There is a cluster of 2 capacitors and what appears to be a diode labelled "D546".


I haven't been able to find a Zotac 2070 Boardview, but I found an MSI 2070 boardview which has a similar cluster connected to the 12V supply consisting of a 4.7uF 603 cap, a 0.1uf 402 cap and 0.001 ohm resistor:

[прямо]

No, that's not the same. On the MSI, that 0.001 ohm resistor is a current sense resistor.

Where exactly did you solder the pin for the fan 12V wire? On the blew up capacitor?

That would have explained why it blew and took out the cap next to it. Cap that size is not able to handle the fan current draw at 50% speed.

You should have soldered the fan 12V wire directly on the PCIE connector 12V pins (bottom row) and not anywhere else.

[tintin_sn2]

Yes, it was directly onto the bottom right 12V pin. If you zoom in though you can see the flux residue I didn't clean at the base of the pad. So I suspect that may be what caused the short.

So in the cluster of three components that blew, could the third component be a diode? The only reference I have is the label "D546" and a marking on the top that says "BEC". All three are connected to ground on the lower side.