Re: laptop fan problem

richgk wrote:
I've just replaced a laptop fan which was occasionaly not working. After
watching it's behaviour for a while I decided on a replace as it would
occasionaly just stop and I thought it was simply that the fan motor was
faulty.

However, the replacement does exactly the same as the original. If you
prevent the fan from turning it switches off and then restarts itself as it
should. I repeated this many times and it never failes to restart.

It seems that rather than the motor being faulty it's actually receiving a
signal to stop spinning. As when it stops in this state you don't see it
attempting to start at all and failing as you might if the motor was
faulty.

Any ideas? This is a clients laptop and it's got me stumped.


I've not come across a computer fan that uses a stop signal. The ones that I have encountered are switched on and off by supplying them with power, or not. They do have a third wire, but that is an output from the fan, not an input.

If the fan spins on power up, then it isn't being controlled by a simple, mechanical, temperature switch but by electronics, eg a thermistor/diode sensor and a comparator.

So, you have several choices:

1) Trace the board back from fan connector to its control electronics and hence to the sensor (or try to locate the sensor by visual inspection) and hence identify the fault. It could be as simple as a dry joint on the temperature sensor.

2) Isolate and reuse the fan connector socket, or provide a new one, going to a replacement thermal switch (either mechanical or electrical) and from there to a suitable power rail.

3) As (2) but without the switch - so the fan runs continuously when the laptop is running. The owner might be happy to trade an increase in reliability and a cooler lap for the slight reduction in battery runtime - particularly as the battery is quite possibly already on the way out.

Personally, I wish manufacturers would provide a "run the fan continuously" option for laptops.

--
Sue

.

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