replacement X220 fan has three wires, not four?

[jkn]

Hi all, greetings from the UK!

I recently bought a S/H X220 Tablet. It had a known 'fan problem' which I am hoping I can fix (I'm an experienced Embedded Systems Engineer and have dismantled Thinkpads in the past, etc.). I have previously read up a bit on the various fan problems, and bought via eBay an x230 CPU fan assembly to see if this would make a difference.

When I stripped down the machine though, I found that the current X220 fan has four wires, but my replacement X230 has only three wires.

For now I have cleaned and re-applied thermal paste, reassebled etc. I am not complaining about the fan assembly I bought, but I am surprised that one model has four wires and one three, especially since the X230 is later than the X220.

- are there variants of these models which might account for the difference?
- might it be worthwhile fitting the three wire fan anyway? I realise I will lose some refinement of fan control & reporting, but wondered if there are any experience with this.

Thanks for any thoughts
Jon N