Recently my main desktop failed, without going into too much detail what happened, I have to replace my motherboard. The trouble is, it’s extremely hard to find the exact same motherboard as the failed one, especially if the computer is a few years old and out of the warranty. When I received the new replacement motherboard (Intel DP67BGB3 ATX DDR3 LGA1155), everything seems to be working fine, except the CPU fan is not spinning.
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There are few places we can start to troubleshoot why CPU fan are not spinning
First, try to eliminate and determine which part is at false. Is it the fan or the motherboard? Is the fan all wired up properly? Is the fan spinning without power? In my case, when I first noticed the issue, I spotted this message:
“One or more fans appear to have stopped or been removed. It is recommended that you inspect the chassis fans to ensure proper air flow.”
I was under the assumption that something was wrong with my fan. But this turns out to be not the case. Do not get fooled by the message that appears to pinpoint you what goes wrong with your system. You can exam this by hooking the CPU fan to another motherboard or if you have the tool, directly connect to a power source to check if the fan is function or not. If it’s not working, then it’s easy, time for you to replace your fan !
However, what if it was working fine with a different motherboard but not on this motherboard?
Second, you should make sure your motherboard is running the latest BIOS. Upgrade if you haven’t. If by upgrading the BIOS the problem goes away, congratulations. But if not, read on.
In my case, I couldn’t get hold off the latest BIOS. Intel’s download support site seems to be down for this particular version of motherboard. I noticed only my CPU fan is not function but other fans are working. The difference between those fans are the amount of power it consumes. CPU fan appears to draw twice as much power as other chassis fans, in my case it uses 0.37 A vs 0.16 A for a chassis fan. It seems the reason my fan isn’t spinning due to the higher power it required.
With this in mind, I started to play around with the numbers in BIOS settings to try to tweak in a way so the CPU fan would receive max power to get it kicked off.
As you can see my CPU fan are at 0 RPM.
What I discovered is that if you override the threshold of CPU fan speed from auto to manual. The fan actually start to responds to the change.
So I started to bump up the minimum duty cycle % to higher than default values.
After many tries, the sweet spot for my fan to keep running is anywhere above 85%. As soon as I’ve changed the fan speed to 100% it kicks off max speed at all time, which is good to have the fan running but not ideal to always have the fan spinning at 100%. If you can bear the extra noise when tuning the fan speed to 100% then it’s ok. If not, you will do quite a bit of experiment to find out the best spot for your machine. In my case 85% seems to be the sweet spot.
As you can see from the screenshot it seems to be working as a result of this BIOS tweak.