Hi Jean, Thank you. Your analysis appears absolutely correct. The fan is speed controlled and problem is pronounced when it is running slowly. Normal speed is around 750-800rpm. The problem appears to diminish as the speed rises; above ~1000 rpm, the readings appear stable. I would assume that Gigabyte have used the automatic control facilities of the it8718 chip. Where is this going to be set up - from the bios? Is there anywhere in the linux system that this can be done? Or is it all automatic. At any rate the thing seems to work, so I don't really want to play with it (let sleeping dogs lie etc). It's just the oscillating reading is a bit annoying. Wouldn't there be anyway of filtering out such values in lm-sensors? (Maybe a configuration setting) Many thanks, Simon On Sat, 2008-05-31 at 23:18 +0200, Jean Delvare wrote: > 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. >
