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Shorting connector and emitter of a laptop fan transistor

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Shorting connector and emitter of a laptop fan transistor

Postby alps » Sun Sep 13, 2015 5:43 am

Hi everybody!
I got a small problem concerning a laptop fan. During the first 30 minutes (more or less) it didn't work properly: it only started spinning immediately after having turned my laptop on after a system shutdown caused by the excess of CPU temperature (excess of temperature obviously due to the "absence" of the CPU fan). But then once on, the fan kept spinning for about 10-20 seconds before stopping again. So, once again the CPU temperature started rising until the forced shutdown. This kind of process occurred 3-4 times in 30 minutes. In this time span, the CPU fan seemed to be in oblivion and only worked at very high temperatures.
After these 30 minutes the fan started working regularly, even for hours!

Explained this problem, someone told me that it could easily depend on cold joints and a reflow of some components would have been the best solution in these cases. But I don't have a hot gun and neither do people I know. So I preferred to do some tests that someone advised.
Then I managed to reset the bios but nothing changed. I forgot to say that in the first 30 minutes my motherboard often blinked (caps lock and num lock).
At last, I found a quicker solution: to short connector and emitter of a darlington transistor that controls the CPU fan:

Now, it would be very intesting to know any possible disadvantage of this choice, such as energy consumption, transistor lifetime (as well as the ones of the other components that might be affected by the permanent spinning of the CPU fan) and other issues that would arise.
Anyway, thanks to a very small piece of copper (the end of a wire) put between collector and emitter, I tested my laptop for a few hours and it seemed that the full-speed fan didn't cause any problem and CPU temperature was well below acceptable limits.
Strange as it may seem, the DDR fan didn't even turn on, perhaps because CPU was always "mild" and so processor didn't give any signal to let the DDR fan start spinning. But I did want even the DDR fan running, so I did the same trick of joining connector and emitter. Now, I have 2 fans at full speed but I need to remove the temporary piece of copper and make this modification definitive.
There is just 1 mm between the 2 pins, so someone suggested to add a drop of solder in-between (without copper or any other material). Is the best solution if I don't want to waste time to unsolder the transistor? Does it guarantee a good electrical conductivity (and then a constant short between collector and emitter)? It should be a micro solder. I got a WS-70DA soldering iron that is not very precise for this kind of tasks. But I am going to practice a little bit before soldering on my motherboard.

Other issue concerns the noise. With 2 fans spinning at full speed I got to wear something to protect my ears... For this reason, someone suggested to put a resistor in order to decrease a bit the speed of the fan. For a DC 5V 0.30A fan, how many ohms should I need? Consider that often the CPU fan spinned at high speed (though not full speed), when my laptop worked in normal conditions. So I cannot exagerate with the ohms. But where and how putting the resistor in such a small available space? And what kind of resistor? Only SMD resistors?
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