I love my Cougar Vortex case fans. But today I'm watching a video on the making of the second Aliens movie when this low pitched screeching popped on. I thought it was the movie at first so I stopped it playing and the noise continued. I cut off the AC and still the noise continued. I put my ear to the side of my computer case and that was where it was coming from.
I am all too familiar with that noise. A fan bearing was about to lock up. I opened HWMonitor and saw one fan had gone from 1600RPM to 390RPM. Whipped out the manual for the mother board to see which fan it was. SYSFAN. That's the top front in my system. I shut down the system and popped off the side panel. I booted up the computer to get a visual on the fans and sure enough I was right. It had stopped dead. Thankfully I have many spare fans new in the box so it was just a matter of swapping it out. Working fine now.
The fan's internal protection circuitry Shuts off power to the coils to keep them from burning up. It will keep trying to start the fan every few seconds. That's why the bios never signaled a stalled fan. Kind of an interesting idea. It keeps the fan from over loading the DC power to the fan and doing damage to the mother board. The draw back is the stalled fan alarm never goes off.
For those of you that have no idea what is under the hood of a 4 wire PWM controlled fan or don't think there's all that much going on, here's a few pictures of what's driving that fan.
Overall view of the driver and feedback board.
Close-up of the micro controller chip.
Close-up of the Hall Effect transistor used to count RPMs.
Cougar Vortex is a very good brand and is an excellent bang for the buck. Its demise was due to some one taking the AC out of my room and leaving the wall mount sleeve open for some time. The air down here in south Louisiana is filthy and very humid. That accounts for the mold and mud that was in my computer and lead to the failure of this fan.
It was not the product's fault.