Help. I have a gigabyte motherboard with AMD XP 1800. I found that my cpu fan speed is going up and down periodically. I goes from 300 to 1200 rpm in a 2 sec cycle. It is a fan problem or a motherboard problem??
Unless you have a fan controller on your system it may be a failing fan,irregular power supply which comes off of the MB usually.
Try a new fan .. go from there.
Your motherboard could also have a fan control technology such as Asus' Q-Fan which lowers the fan's speed when the CPU is running cool & speeds it up when the CPU starts to get hot.
