Normally the heat sink fan would run at full speed when I start the pc but only for few seconds and the sound is really audible at full speed then it would slow down and is silent from there on.

But now, when in use, even if I am just browsing or even when the pc is idle the fan randomly runs at full speed for few seconds then it goes silent, this keeps happening every 5/10 minutes and it's really annoying.

I used Open Hardware Monitor program to check the temperature and it shows the CPU's max temp is 50C and when in use the temp fluctuates around 36C - 42C, this I think is an acceptable temperature for the CPU.

I assembled this pc myself in 2012 and this is the configuration:

  • Cooler Master CM690-II Advanced Mid Tower Cabinet
  • Gigabyte GA-H77-DS3H Motherboard
  • Intel 2.6 GHz LGA 1155 Dual Core G620 Processor

I would really appreciate if someone could help me troubleshoot this issue.



The problem was with the heatsink fan, it would would stop intermittently and then start again at full speed and this kept repeating every couple of minutes. So I bought a new heatsink fan and it solved the problem.


How about the System temperature? It can turn the fan onto a higher speed, too. The other possibility is either the sensor in the board (which is very rare) or the tachometer feedback from the fan itself. One of the wires on the fan is used as a tachometer to measure the speed it is running at and, if it goes bad or flakey, the PC loses what speed it is running at.

  • The section below Motherboard which says ITE IT8728F says three temperatures which are around 32C, i think this is system temp. – Raj Sep 19 '16 at 13:32
  • Then the hope is that its the speed sensor (tachometer) in the fan. You can try blowing the dust out from underneath the fan's center (on most, I can see the circuit board if I look closely); but, the surest approach would be to replace the heatsink and fan assembly. ebay.com/itm/… – DavisMcCarn Sep 20 '16 at 10:46
  • I removed the heatsink, cleaned off the old thermal paste and applied fresh thermal paste on the heatsink, unfortunately this didn't work either, so I removed the cabinet's side panel when the pc was running, to see what's going on, what I noticed is that the fan stops running for few seconds, it twitches for few seconds then it operates at full speed. – Raj Sep 22 '16 at 3:16
  • This page has pictures and a description of how the cooling fan works: pcbheaven.com/wikipages/How_PC_Fans_Work I think the hall effect sensor is either faulty or dirty; but, the easiest test is to buy a new one. – DavisMcCarn Sep 22 '16 at 11:27
  • Thanks Davis, it turns out that the heatsink fan was the problem, as I mentioned it was stopping intermittently, so bought a new heatsink fan and that fixed the issue. – Raj Sep 28 '16 at 14:45

This could be due to dust and/or other particles accumulated onthe fan blades.

If this is the case, use a blower to clear the dust off the fan blades and you should be fine.

  • Yes, obviously opening and cleaning the cabinet thoroughly is the first thing I did but it happens sometimes and sometimes like at the time of writing this it's working smoothly. – Raj Sep 19 '16 at 13:33

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