What does this Laptop CPU fan wire do? - Page 1
Forum section: electronics / beginners

author: Dokroma
author_rank: Contributor
timestamp: September 12, 2020, 03:29:27 pm
content: 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!

author: Dokroma
author_rank: Contributor
timestamp: September 12, 2020, 03:31:11 pm
content: one

author: Dokroma
author_rank: Contributor
timestamp: September 12, 2020, 03:32:01 pm
content: two

author: Dokroma
author_rank: Contributor
timestamp: September 12, 2020, 03:33:49 pm
content: due

author: Dokroma
author_rank: Contributor
timestamp: September 12, 2020, 03:35:06 pm
content: 4

author: Dokroma
author_rank: Contributor
timestamp: September 12, 2020, 03:36:26 pm
content: 5

author: fordem
author_rank: Regular Contributor
timestamp: September 12, 2020, 04:20:02 pm
content: 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.

author: JimRemington
author_rank: Regular Contributor
timestamp: September 12, 2020, 04:29:51 pm
content: My guess is thermocouple or thermistor leads. The fan would turn on only when some threshold is exceeded.

author: Dokroma
author_rank: Contributor
timestamp: September 13, 2020, 10:10:58 am
content: Bump, but if it was a thermistor wouldn't there have been two wires?

author: Jwillis
author_rank: Super Contributor
timestamp: September 13, 2020, 02:16:17 pm
content: Quote from: Dokroma on September 13, 2020, 10:10:58 amIt would just tie to the ground . Two wires would be unnecessary .WiFi ?

author: Twoflower
author_rank: Frequent Contributor
timestamp: September 13, 2020, 03:57:51 pm
content: My wild guess would be the wire is grounding the heat-pipe.

author: Gyro
author_rank: Super Contributor
timestamp: September 13, 2020, 04:22:06 pm
content: Quote from: Dokroma on September 13, 2020, 10:10:58 amIt 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.