How to control VF-700 /w HD 3870? (3-pin vs 4-pin)

[CheeseWeaver]

Hello!

I got an ASUS Radeon HD 3870 a week ago, as it has quite low idle power and apparently rather quiet stock cooling.

However, I forgot about my NB heatsink which apparently makes the stock 2 slot cooling not fit in my chassis. (The NB is behind the upper PCIe slot)

I researched which 3rd party heatsinks work with HD 3870, and apparently VF-700 and VF-900 does.

As wanted to get my new video card to work as soon a possible I picked up a VF-700 AlCu from a local store (it was the only thing they had in stock that fit.)

It fits perfectly, especially as the HD 3870 has really nice memory heatsinks.
However, the zalman has a standard 3-pin fan connector whereas the stock cooling uses a slightly more unusual smaller four-pin connector, and ideally I want to control the fan voltage with the video card.

So far I have the AlCu connected straight to 12V which is horrible noisewise. Is anyone familiar with the pinout of the four pin connector on ATI cards?

This guide -> http://www.hardwaresecrets.com/article/496/1 mentions that motherboard 4-pin fan connectors usually work like this:

Pin__Function_________Colour
1____Ground___________Black
2____+12 V____________Red or yellow
3____Fan Speed Sensor__Yellow, white or green
4____PWM Control_______Blue

This enables 3-pin fans to function at 12V, while 4-pin fans are controlled by PWM. We are talking about CPU/Chassis fans though.

The Stock GPU fan's four connectors are coloured
Black
Red
Yellow
Blue

The Stock fan has quite a bit of circuitry in the fan itself, so i figure that the video card constantly outputs 12V on the red line and the speed is governed by the PWM line, probably going at full speed when the blue line is unconnected.

Does anyone know on any of these pins output a variable voltage according to the ATI driver? If this is the case it would be trivial to build a 4-to-3 pin adapter that allows the VF-700 to run at a slower speed.

However, it would be a lot easier to simply implement PWM on the video card instead of constantly varying the voltage.

Hence, does anyone know how ATIs video card PWM is implemented?
I really ought to get the computer hooked up to my oscilloscope to check it out, but first i have to make a four-pin-male extension cord.

It would be interesting to implement my own solution to control any 3rd party fan's voltage by the on-chip PWM output. I'm not scared of soldering or anything like that (i'm a 3rd year electrical engineering student) and it would sure be an interesting project.

Of course, it would be very much easier to connect the VF-700 to a front panel fan controller or to do something with a thermistor and voltage regulator.


Well, does anyone have any ideas? :?:

[quikkie]

while you figure it out you could use the 12/5V "octopus" that should have come with your vf700.

[SebRad]

Hi, I would start by doing the trivial connection of the fan to first 3 pins on the card to make sure the card is using 4pin PWM control. (if it is the fan will spin full speed regardless of fan-speed setting)
If it is I see three options:
Fix the fan speed (5v, 7v, fan controller etc) to a speed that cools enough under load.
Use an adapter, I have seen (but can't find again) a 4 pin to 3 pin adapter that takes the PWM control signal and changes it to voltage control.
Change the fan on the VF-700 for a PWM one. There are several threads where people have fan swapped VF-700s & VF-900s (my VF-900)
Regards, Seb

[pipperoni]

The ATI connector is the same as the Intel 4 pin PWM connector, I know because I have my 92mm NEXUS fan hooked up to the same type of video card with an HR-03. The fan will run at full speed though as there is no automatic control without a 4 wire fan. I put a resistor in the power line, but ideally I would like to find some updated software like ATI Tool, ATI Tray Tools or AMDGPU Tool that would let me automatically set the speed based on temperature.