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Electronics => Beginners => Topic started by: Dokroma on September 12, 2020, 03:29:27 pm

Title: What does this Laptop CPU fan wire do?
Post by: Dokroma on September 12, 2020, 03:29:27 pm
Yesterday, I opened my laptop to clean it up and replace the thermal paste. It's a Lenovo Thinkpad. When I had put everything together, I left the bottom panel off just in case it didn't boot properly. Everything was fine but I noticed the CPU fan only span for a second on boot up and then stopped(I later learned this was normal) I thought I may have not put something back properly. I then disassembled everything and I noticed I broke this really small 0.3mm wire. The wire is soldered near the rest but it is taped onto the copper heatsink. When I had cleaned the CPU fan and was screwing the top plate back onto the bottom, this small exposed wire got caught in the screw and it tore the wire in the middle. I repaired it by taking a larger 1mm wire and soldering it on one end of the small wire and reconnecting the other end of it to the heatsink, not with tape but with solder. It was difficult to solder to the copper pipe, I had to sand it down and use flux but it was still a struggle.



I was wondering what the purpose of the wire was? I thought maybe it would detect heat and spin when it noticed the copper heatsink got hot? I have attached photos of it. It is the wire next to the white PWM wire. It was taped to the copper heatsink which I took a photo of.

Edit: It won't let me attach all the photos!
Title: Re: What does this Laptop CPU fan do?
Post by: Dokroma on September 12, 2020, 03:31:11 pm
one
Title: Re: What does this Laptop CPU fan do?
Post by: Dokroma on September 12, 2020, 03:32:01 pm
two
Title: Re: What does this Laptop CPU fan do?
Post by: Dokroma on September 12, 2020, 03:33:49 pm
due
Title: Re: What does this Laptop CPU fan do?
Post by: Dokroma on September 12, 2020, 03:35:06 pm
4
Title: Re: What does this Laptop CPU fan do?
Post by: Dokroma on September 12, 2020, 03:36:26 pm
5
Title: Re: What does this Laptop CPU fan wire do?
Post by: fordem on September 12, 2020, 04:20:02 pm
See where the ends go - quite a few of the Lenovo laptops run the WiFi antenna leads around the edge of the fan housing and that looks like one of them.
Title: Re: What does this Laptop CPU fan wire do?
Post by: JimRemington on September 12, 2020, 04:29:51 pm
My guess is thermocouple or thermistor leads. The fan would turn on only when some threshold is exceeded.
Title: Re: What does this Laptop CPU fan wire do?
Post by: Dokroma on September 13, 2020, 10:10:58 am
Bump, but if it was a thermistor wouldn't there have been two wires?
Title: Re: What does this Laptop CPU fan wire do?
Post by: Jwillis on September 13, 2020, 02:16:17 pm
Quote from: Dokroma on September 13, 2020, 10:10:58 am
Bump, but if it was a thermistor wouldn't there have been two wires?

It would just tie to the ground . Two wires would be unnecessary .
WiFi ?
Title: Re: What does this Laptop CPU fan wire do?
Post by: Twoflower on September 13, 2020, 03:57:51 pm
My wild guess would be the wire is grounding the heat-pipe.
Title: Re: What does this Laptop CPU fan wire do?
Post by: Gyro on September 13, 2020, 04:22:06 pm
Quote from: Dokroma on September 13, 2020, 10:10:58 am
Bump, but if it was a thermistor wouldn't there have been two wires?

It could be a thin twisted pair or coax - it all hangs on what the connector is at the other end (and where the other end is).

It could also have been connecting to a thermistor with one side grounded to the heatpipe.