A New Plan?

Remember that one time when I fried a 6850 graphics card? In short, I was switching to aftermarket cooler, and I had to fiddle with VRAM heatsinks so they would fit properly on my card. Something got shorted along the way and the card was done.

After which, I bought an Asus 6870 DirectCU. I was carefully choosing a card with good stock cooling so I wouldn’t need to touch it. Well, it is reasonably quiet, but by now all the other components have gotten quiet enough that the card is again the most noisy component. Hacking time again, eheheh?

Here are my options.

I could sell this card, and get a semi-passive Asus STRIX series card. The fans on these don’t even spin up at idle, which would be perfect. It’s a bit of investment, but, frankly, this is probably the sanest option to take.

I could do something about the stock cooler, stock heatsink, or the cooling profile. On reference-design cards you can use Radeon BIOS Editor to create a custom cooling profile and upload it to the card. The cooling profile could be something like “don’t spin fans until 65C, then ramp up, reaching full speed at 75C”. This would effectively convert a regular card into semi-passive card. The card would need to have a good heatsink to have thermal headroom, so it can run passive for useful amounts of time though.

Problem with custom desigs like my Asus DirectCU is they use custom cooling solution, and custom fan controller that you can only partially control from card’s BIOS. In particular, even at 0% duty cycle the fan will spin at 1300rpm. The fan controller is designed to range between 1300-3000rpm, which corresponds to 0%-100% duty cycle. What’s more, there is a feedback loop from tachometer to PWM signal. The fan controller will maintain fixed idle speed and will ramp up duty cycle if fan slows down. So, even if I replaced the stock fan with a slower-running, quieter fan, the controller would still spin it at 1300rpm.

Due to heatsink design, there is also not much improvement to be had from switching fans. It’s already about as good as it gets with this heatsink.


You cannot switch out from 8.5cm fan to a couple of silent 12cm fans because top of heatsink is not flat and the plastic shroud is also there for a good reason. The dual fans would probably do a worse job at cooling, and, yeah, they would still spin at 1300rpm.

An aside: an interesting observation was how the plastic shroud is attached. Its screws are located so inconveniently, you pretty much have to remove the whole heatsink to access them. Why make it difficult? I guess it is to stop people from removing the shroud, messing up airflow, overheating the card and then claiming warranty. It’s as if the card’s designers said: “there is no good reason to remove just the plastic. You would only be doing that if you’re also changing the whole heatsink”.

So you could change the whole heatsink but there’s no way I’m doing that, after what happened with 6850.

How about using motherboard’s chassis fan connectors for GPU? Well that might work, but there’s two potential issues. First, the GPU might get upset “dude where’s my fan” and throttle back its performance. Second, it would be a brittle setup, where some resident software polls GPU temperature and controls the chassis fan. This is a GPU meltdown waiting to happen.

Now, as I said, the rational choice is probably to splash out for a STRIX card and be done with it. But for one last idea, how about MitM-ing the GPU fan controller? It appears that Arduino style devices have the required hardware to read PWM signal (perhaps with a help of small resistor and capacitor, to convert to analog first). It can also output PWM signal for driving fan, and surely it can output pulses to imitate tacho. So there could be an Arduino sitting on the wire before GPU fan, listening on the trusty but way too conservative PWM signal from the card, then doing its own custom curve and reporting fake tacho numbers back to keep the card happy. Now that would be a hack!