A couple of days ago, I turned the PC on (I thought it was off but it was only sleeping) and the alarm started and didn’t stop. It’s an annoying pinging noise, not terribly loud but irritating. Figuring it was a thermal problem, I opened the case (it has a quick-release handle but you have to take out two thumbscrews first) and looked at the CPU fan. It was stopped. I gave it a flick but it didn’t start (and there was nothing getting in its way). So I rebooted.
Then the alarm kept sounding on and off through the day. The fan kept stopping and starting but it really didn’t seem to matter. So, I started playing with the Gigabyte EasyTune5 application. This is the only fan speed and CPU temperature monitor I can find so far (Believe me, I’m looking for a better one. EasyTune5 is a “triumph of form over function” and it’s really ugly.).
What I found was the CPU temperature runs about 24-26 deg C under the low load of sitting here watching the temperature. When the temperature drops to 24, the fan stops and the alarm goes off, but the CPU still takes a while to get back up to 25. So I played a DVD to increase the load, it hardly made a difference. DVD’s put a 5-10% load on each core. The temperature drifted up to 27 and back down to 25. Playing Second Life brings the temperature up to 37, so that’s one solution.
I used EasyTune5 to increase the minimum fan “effort” from 28% to 50% (at 20 deg C). I’ve heard hardly a peep since then. It appears the fan is “undervolted” at low temperatures and stalls. However, it’s a 4 pin fan and I thought they ran on PCM instead of variable voltage. I’ll study more on this subject, later.
BTW, the system temperature was running about 43 deg C and the nVidia GPU was 59 deg C (it has no fan, just a big convection heatsink). Ambient was about 21-22.
One of the reasons I chose Intel over AMD was the 65W TDP (compared to 125W for Athlon 6000) but I never expected it to run this cool. Pat Gelsing made a famous quote a couple of years ago about Pentium 4’s being “hotter than the sun” by 2010. I’m really impressed by the Core 2 Duo.
Update 13 Oct 2007
A couple of reboots ago I changed the fan settings in the BIOS from “Auto” to “Intel something” and “PWM” (Pulse Width Modulation, I assume). The fan alarm now pings for a fraction of a second on power up and wake up. CPU Temp now runs in the high 20’s, with the fan in the 800’s, under low load. A much more satisfactory arrangement.
Update 6 Jan 2008
Based on the comment I received here, I should provide a little more explanation. Normal DC fans can be speed controlled by varying the voltage. Most people would have had experience with model trains and slot cars; the controller is just a variable resistor, changing the voltage available for the motor by creating a voltage drop across the controller. However, the speed response of the motor to the change in voltage is only linear over a small range. Again, model trains and slot cars display really poor slow speed running; they just stall. So do PC fans. The solution is to switch the current on and off (at a high enough frequency so the stop-start characteristic is not observed) while maintaining the voltage. This is Pulse Width Modulation and it provides very fine and accurate speed control.