I bought the components second-hand and I'm trying to determine whether the motherboard is faulty. I'm using a four-pin Thermalright TL-9015 PWM fan directly on the CPU fan header of an MSI B450I AC, with no splitter or hub. I enabled Smart Fan Control, selected PWM mode, chose the CPU as the temperature source, and configured a fan curve of 20%, 35%, 75%, and 100% at 0°C, 20°C, 65°C, and 80°C. However, the fan stays around 1,000 RPM regardless of the temperature or curve settings. The same thing happens with another Corsair PWM fan and on the system-fan header. Switching the header to DC mode makes the fans stop completely. I removed other fan-control software and only have Core Temp running in Windows. Is there a BIOS setting I'm missing, or could the motherboard be defective?
2 Answers
The fact that DC mode stops the fan suggests the header is responding to the selected control mode, but PWM mode may not be applying the curve correctly. Confirm that the BIOS changes are saved and still present after reboot, then test with the fan running at minimum and maximum duty settings while watching the reported RPM. If two separate four-pin fans behave identically on both headers, the BIOS configuration or motherboard firmware is more likely than both fans being faulty.
First, make sure the fan is connected directly to the header rather than through a hub or splitter, and verify that the header is actually set to PWM rather than DC. It’s also important to configure the temperature targets and curve points, since a low target temperature can make the fan run faster. Testing another known-good four-pin fan is a useful way to separate a fan issue from a motherboard issue.
The fan is connected directly to the CPU header, and I also tested the system-fan header. I tried another Corsair PWM fan as well, but both fans remain at the same speed even when I set every curve point to 100%.
I tested both headers with the same result and used the listed PWM settings. Even forcing the curve to 100% does not change the approximately 1,000 RPM reading.