Hi Simon, On Wed, 28 May 2008 09:39:45 +0200, simon wrote: > The following output shows periodic output from sensors for my CPU > cooler over a short period. > > The value continually oscillates between a real value (around 720-750 > RPM in idle) and out-of-range values 337500 RPM/675000 RPM. When the > machine is loaded, and the fan spins faster, the fan value stabilizes at > a normal value. > > The fan 2 sensor has no problems. What's the usual speed value of fan2? Does its speed also change according to the temperature? The problem typically only shows for fans those speed is controlled and only for low speeds. > Anyone have any ideas what's happening? > > Configuration: > lm-sensors v3.01 > Motherboard Gigabyte GA-MA78GM-SH2 > CPU Cooler: Thermaltake TMGA3 (3 wire) > > Output from sensors over ~2 mins: > it8718-isa-0228 > > fan1: 726 RPM (min = 0 RPM) > fan1: 675000 RPM (min = 0 RPM) > fan1: 337500 RPM (min = 0 RPM) > fan1: 738 RPM (min = 0 RPM) > fan1: 675000 RPM (min = 0 RPM) > fan1: 726 RPM (min = 0 RPM) > fan1: 675000 RPM (min = 0 RPM) > fan1: 337500 RPM (min = 0 RPM) > fan1: 675000 RPM (min = 0 RPM) > fan1: 725 RPM (min = 0 RPM) > fan1: 725 RPM (min = 0 RPM) > > Many thanks for ideas! This happens frequently when you control the speed of a 3-wire fan and the speed drops below a given limit. The speed is measured using a signal that comes from the fan, and when you control the fan, that signal gets weaker (think of it as proportional to the speed of the fan). So apparently your fan is exactly at the limit below which the signal is too weak for reliable speed monitoring, which results in these fancy readings (which really mean that the IT8718F chip fails to sense the speed signal). If you can change the settings of the fan speed control so that the idle speed is slightly higher, the problem should go away. If the fan self-regulates then there's unfortunately not much you can do. As a summary, 3-wire fans cannot always be controlled and monitored at the same time reliably. That's why we start seeing 4-wire fans, which do not have this problem. -- Jean Delvare
