DIY: Cpu fan replacement

Dec 19

We have another DIY article based on something that happened to my older backup computer. Between loose wiring, dirt and curious fingers – the fan lost 2 blades and caused the whole PC case to wobble shaking the video card out of agp port causing crashes.

The cost of this DIY is $0 assuming you have the right tools, dead power supply (with a working 12 volt fan) and some electrical / soldering experience. Please note several things:

  • Unplug the power supply you will take apart from the outlet!
  • Power supplies contain capacitors which can still contain enough charge over time to give you a good jolt if you don’t pay attention while touching terminals. Don’t touch the terminals by hand – use isolated wire cutters.

My backup PC uses an old sempron 2500+ with 3.2″ length & width heatsink, so the power supply 12 volt fan is just slightly bigger than the stock cpu fan I had on there originally – more cooling is better :) Below is the picture of the fan I have currently on there (also an upgrade however it’s dirty & abused).

After removing the fan & heatsink from the cpu – I’ve thoroughly blown out all the dirt using air compressor. I then removed the old damaged fan from the heat sink. Here is a fan I took out from another power supply just to give you an idea that most power supplies come with similar size fans. Test your fan with 12 volt voltage source (any 12 volt power supply will do or use the computer power supply).

Here is what we will do – find a way to attach the next fan on top of the existing heat sink. Now you have 2 choices – use it in “push” (push colder air from top onto the cpu heatsink) or “pull” (pull hot air from the heatsink, which gets replaced with colder air around it) configuration. I chose the “push” configuration since I think it has some advantages.

As you can see – it would take a bit more work to make a bracket so that we could use screws to hold the fan to the sink. We’ll have another way to do it which is equally reliable.

If you look closely, you will notice that the sink fan has small hook ledge where the factory bracket was held. The issue is that you cannot just push the fan into the holding ledge or will be held too close against the sink.

So I used a small metal saw to create 2 ledges on the opposite sides of the fan so that it would be held in place above the heat sink.

Now let’s line them up – you may need to gently expand the heat sink to fit your new fan over the center of it – in my case it didn’t take much time to do this with the fans being similar.

You can see the clearance from the heatsink that we have thanks to the ridges we created. Once you snap it in – should be very stirty – to give you an idea – you need screw driver and some effort to take out again. If it is loose – bend the sides of the heatsink so that it grabs well.

This is what it looks like from the side. You can see my goof up when making the first notch 😉

Now we need to test to make sure the wiring we transferred from the old fan still works. Note that I am not using the 3rd wire (blue) in this case (which is the rpm measurement that my new fan doesn’t have).

Temporarily wire the power wires for the test but keep them separated when you plug it in. You can use isolation on the wires as well to prevent them contacting each other.

Quick test to ensure the fan positive and negative follows the standard color code. What we are looking for is to check whether air is being push onto the heatsink & out to the sides (“push” configuration). Keep wires separated for the test & don’t keep the computer on too long since CPU doesn’t have a way to cool itself.

Ok, test went as expected. Now let’s solder the wires from the new fan to the old connector. I am using shrink tubing to cover the exposed area of the wires but you can use electrical tape instead – shrink tubing helps to keep moisture out to lessen the chance of contact & a short circuit.

If you are using shrink tubing, put it on the wires before you solder…

After soldering, place the shrink tubing over the soldered areas & “shrink” them using heat…

Now add heat paste between the sink & cpu, mount your fan / heatsink combo back in place & hook it up.

Now enjoy your new found quiet fan. I noticed that after blowing out the dust, doing upgrading the fan & adding heatpaste, my cpu temperature dropped 7 degrees. It’s been running for over 12 hours with slight overclock without issues.

*** Short update: system works great over 48 hours later while overclocked.. Temperature of CPU still 7 degrees below & no crashes.

Oh yeah – Merry Christmas!!!