I purchased 3 ARCTIC COOLING AF12025 PWM 120mm Case Fans to daisy chain on SYS_FAN2 as intake fans, set the BIOS on PWM fan control but no go. You can feel that the fan is almost getting enough power to turn but will not keep spinning on its own. Also no go if don't daisy chain and use only one fan. The CPU PWM fan works as it should, regulated by the CPU temperature. If I plug an ARCTIC COOLING PWM case fan into the CPU PWN outlet, it works fine. The fan instructions say if the fan turns less than 1000rpm, don't use it daisy chained. So, where is the sensor that controls SYS_FAN2 and how does it work? I can find no other control in the BIOS other than set fan mode to 'auto' or 'PWM', which I set to 'PWM', and the CPU PWM fan woks fine. This is not a big issue, I just wanted my intake fans to be quiet when system temp is low, but if I wire them PWM they don't seem to work at all.

I have the same MB. I have an AF12025 and 2x AF8025 daisy chained to my AF7 freezer pro. (PWM works great with Speedfan, Smartguardian - the MB control - is good too.)

P35-DS3l has only one PWM enabled fan-header - the 4pin CPU one. The 3pin SYS-fan2 will not work - the fan speed control electronics are just not there, the BIOS only supports fan control for the CPU fan-header, and in any case sys-fan2 does not supply 12V.
http://forums.tweaktown.com/f69/ga [...] rol-25612/
One of the negatives of a budget board I'm afraid.

I have the last 3pin adapter on my daisy chain attached to the sys-fan2 header to read RPMs for my Intake fan (plus a 40 mm fan for my Northbridge attached with a y adapter).

To cut a long story short unless you have an AF7 CPU cooler you are out of luck; either buy an AF7 and daisy chain or return those AC fans and get a fan controller for your old fans.

BTW I had no idea what you were talking about with the no go if don't daisy chain, less than 1000rpm part of your post.

Thanks for the reply! Now I know I didn't just do something dumb so it wasn't working. The post you linked is exactly the same problem I have and explains it is the fault of the Gigabyte board. My motherboard has both CPU and SYS_FAN2 as 4 pin PWM connectors, but as pointed out by the linked post, SYS_FAN2 does not appear to be properly controlled and has insufficient voltage. No big deal. Used other 3 pin fans on 3 pin headers and let it go. Not as quiet as I would like, but OK. The daisy-chain part I put in was pointing out that not chaining the fans together did not fix it. The instructions with the fans said if they run below 1000rpm continuously, do not daisy-chain. Why?, I don't know! Thanks.

One thing to understand is that PWM pules the fan, thats why it tries to go, its not a voltage thing but that fact that the fan will not get moving with pulses so far apart. If the system is put under load and the temperature goes up the fan may well kick in as the pulses happen faster due to higher system temps.

With a early bios for the DS3r my cpu fan did not spin, just pulse like that until it was working and hot enough. no harm done. low voltage could overtime hurt, but i think pwm is safer with its pulsing. That said this may have been fixed with a bios update.

My suggestion is to try speedfan to set it to software control then you can set it where you want it...and even set speedfan to do this on its own in the future. OR use a fan controller to get just the speed you want.

Unruly Peasant, That board DOES have two 4 pin PWM headers. One hides near the ram slot
Look at the red outlines

Thanks for that info Nukemaster, I was confused. I had just installed my fans then I read your post and had to do it over. My 120mm intake is now connected to SYS_FAN2 and spins up as soon as Speedfan starts, it works fine.

funny, just yesterday i added an intake 120mm fan to my case. n yeah, the only place i could add was SYS_FAN2. but it will never reach it's full speed. NEVER, even with speedfan. the only way to make it spin at full speed, is to connect it to the normal power cords (same one going to harddisk, etc). but if u connect it to that, u wont be able to control the speed, nor u can c the rpm. anywho, im using speedfan to make it spin at 1100rpm, instead of the full 1800rpm.

When I fist built this rig about a month ago, I set the 3 PWM case fans as intake daisy-chained to PWM SYS_FAN2 and set the BIOS to PWM fan control. I let it rum that way for a day but the PWM intake fans would never spin up even with games. I then daisy-chained one PWM case fan with the PWM CPU fan and it would spin up about half way. Now it is possible that the case simply never got hot enough as I am using an Intel Wolfdale 45nm processor, but I was uncomfortable with no spin at all. I tried only one fan connected to PWM SYS_FAN2 and it would never spin up with games, etc. I did not try Speedfan, I just rewired my fans at that point. If Speedfan works, then logic says this is a BIOS fixable problem. Too bad it doesn't work. My idea was to have PWM fans for CPU and intake, the two temperature controlled exhaust fans. This set up should be quiet at ideal and energy efficient, but it doesn't work as I feel it should. Thanks again for all the replies.