VPCZ1 Fan cycling on-off every 4 seconds or so

I recently opened up my laptop because the fan had stopped rotating. I dismantled and cleaned the fan and cleaned and lubricated the shaft. When I reassembled it, all went well for a couple of weeks. I ran PCMark07, and a few full HD videos; no problems.

Yesterday, the laptop shut down on speed mode. Upon investigation, I found that the fan is switching on-off every 4 seconds or so, about 16 times a minute. This is fine for the stamina mode where the amount of heat to be expelled is not much, but when I enter speed mode the laptop switches off in a few minutes. Previously the fan would run full blast every now and then and bring the temperature down. Now it is just the same 2 seconds on, 2 seconds off cycle.

Can anyone tell me what is going on? Is the fan motor overloading due to a stiff mechanism/ sticky shaft and tripping repeatedly? Or is this a software issue? I have recently installed Visual Studio 2010 and 2012, besides some more embedded development stuff. (These entailed several GB of updates, so I'm not keen on doing a clean install anytime soon).

 

I struggled with this for quite a while. I even dismantled the laptop and lubricated the fan again, to no avail. Looking at the fan with the keyboard raised up I could see that the fan was rotating very slowly, and would even stop dead on occasion. Stamina mode idle temperatures would touch 80 deg C. Speed mode would kill the laptop in less than a minute, even on idle.

After trying all kinds of things, I gave up and decided to see if it would download stuff at least. So I fired up qBittorrent (the Bittorrent client that I'm currently using), and Oh joy! the fan suddenly kicked into full blast. Within 30 seconds the temperature dropped from the high 80s down to less than 50. Idle temperatures are back to normal (about 40 in stamina mode; 50 in speed mode - which is OK for an ambient temperature above 30).

It seems that the motherboard had somehow stopped communicating with the embedded controller that controls the fan. Running qBittorrent restored that comm link, or reset the controller, or something. Anyway, once it became OK, it has stayed OK. I don't need to run qBittorrent in the background like I did for the first few days. I have played games and run demanding applications and benchmarks; everything is working fine.

Thanks to all who helped me sort out this mystifying problem.
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wait a minute
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nvm