After moving my high-end PC, I removed the GPU and the two fans from my DeepCool AK620 cooler. While reinstalling them on an ASUS ROG STRIX B650E-F Gaming WiFi motherboard, I accidentally connected the fan cable to an RGB header. The fans did not spin, so I shut the system down immediately and connected them correctly through the CPU_FAN header using the cooler's Y-splitter.
Both fans now spin and respond to CPU load as expected, but the system still enters BIOS because it detects 0 RPM from the CPU fan header. I had to set the CPU fan low-speed warning to Ignore before Windows would boot. Fan Control also reports 0 RPM, although it still shows the configured fan percentage changing from around 25% to 100% and the fans visibly respond to the curve.
Could the incident have damaged the fan tachometer signal, the Y-splitter, the motherboard header, or the fans themselves? Is it safe to keep using the computer if the fans are spinning normally, and is there a way to identify which component failed?
2 Answers
The fans are probably receiving the PWM control signal but no longer sending a usable tachometer signal. The percentage shown by Fan Control is the requested duty cycle, not a measured fan speed, so it does not prove that the fans are actually running at that percentage. If the fans visibly spin and CPU temperatures stay normal under load, the system is unlikely to be harmed, but you should continue checking temperatures and make sure the fans do not stop unexpectedly.
Try testing the two cooler fans separately instead of using the Y-splitter. Connect one fan to CPU_FAN and the other to CPU_OPT or the second CPU fan header, if available. The primary header may provide the main control and warning signal while the secondary header is linked to it, though its RPM reporting can vary by motherboard. If one fan reports RPM when connected alone, the splitter or the other fan’s tach wire is the likely problem.
Replacing the Y-splitter is a reasonable first step because it is inexpensive and easy to test. If neither fan reports RPM when connected directly to a known-good fan header, the tachometer circuitry in the fan or the motherboard header may have been damaged.
I can see the fans clearly beside my monitor, so I would notice if they stopped. I’m mainly trying to determine whether the likely failed part is the header, splitter, wiring, or one of the fans.