Issue with fan controller on an MSI GTX 970 4GD5T

MSIGamer72

n00b
Joined
Feb 6, 2021
Messages
20
Hi all, been trying to get into electronics repair recently, it’s always something I’ve wished I was good at.

I’ve been trying to get into GPU repairs recently and have picked up the above card from eBay. The seller was selling because it wouldn’t load driver in windows after he shorted the fan header with a metal retention clip from a SATA cable, so I thought I’d be able to narrow down the issue reasonably well. Plus it was a cheap buy.

Initially I reflashed the bios as it wasn’t installing drivers. The current bios version is the latest one for the card (the original version on the card wouldn’t fully display all bios info on GPU-Z). This got the card up and running again, but I’m now trying to get to the bottom of another issue caused by the short.

When the PC loads, the fans run at idle, but as soon as Windows starts up, they spin at 100%. I’ve tried the usual re-install drivers using DDU and a fresh install, I’ve also tried reinstalling windows. I have a spare set of fans from another GPU, which also spin at 100% on loading windows (can’t confirm they don’t also have a similar issue as I’m told they also spin at 100% on the GPU they came off of).

I suspect it is a hardware-level fault and I’m stuck in trying to locate the fan controller. My electronics knowledge is minimal but I have to assume the issue here occurred when the fan header was shorted with the SATA retention clip, possibly sending 12V somewhere it shouldn’t have, like perhaps the tachometer sense line.

I’m not sure if the tachometer signal is interpreted at a set of components that act as the fan controller or by the GPU die itself.

Any ideas where to start trying to locate a possible fan controller?

I’m currently using the GPU connected to the cpu fan header and maintain around 73 degrees C on gaming, but the whole point is to try and fix the original issue.

If I remember correctly when I last checked about 2 weeks ago, the pwm line shows about 2V at idle (before loading windows) and shoots up to about 3.3 V on loading Windows with fans running at 100%. I do have a cheap oscilloscope I could use to look at the PWM signal if needs be.

I’ve uploaded pics of the back of the board where I think there may be an issue. If you need more pics, I have plenty so feel free to ask.

By the way, the red cable you're seeing tucked behind the fan shroud was my attempt at running a new tachometer wire to the fan header to rule out an issue with the cable itself. It's not currently connected to anything as the original wiring doesn't seem to be at fault.
 

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RazorWind

2[H]4U
Joined
Feb 11, 2001
Messages
3,856
Is the fan header the through hole component you have circled in red in that second photo? Where do those traces leading away from it go?
 

MSIGamer72

n00b
Joined
Feb 6, 2021
Messages
20
Hey, that's right, I've re-marked it here for clarification. I'll re-check the traces tomorrow and get back to you. Last I checked, one (either tach or pwm) appeared to go to the area highlighted at the top, and the other went to the right side of the board, with one of them also showing continuity to one of the legs on the bios chip itself.

EDIT: judging from the pic itself, the pwm trace seems to go to the "suspect area", and therefore the tach line went to the right of the board to some sort of component (transistor?).
 

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