This guide will only be of help if you want to do fan cleaning.
There’s no reference of replacing the motherboard.
Be careful when you disassemble the laptop.
And make sure the laptop is turned off.
I’ve prepared those tools to help cleaning.
Silica gel, the full set of screws for ThinkPad T420, screwdrivers and curved hard wedge.
Now I’ll start from the bottom.
The common sense of disassembly: remove the battery, the memory cover, the hard drive and the optical drive.
And then according to below picture, remove all the screws.
And you can leave them in the position how they located in the bottom cover.
Now, turn it over, unload the keyboard.
First push hard forward as the picture shows. Once the bottom of the keyboard is loosen, the keyboard can be unloaded.
Do remember not to rush.
There are cables connected still. Pick it up following the arrow.
After remove the keyboard, remove 3 screws marked below.
Use fingernails to gouge the C side cover out on the front of the laptop.
And there are cables too. Just pull it up with a little force.
There’s a little screw beside the fan.
And the screw on the left louder speaker.
Unplug the connector connecting the screen, pull it up.
Remove the louder speaker.
And the screws here.
Now I’m able to remove the radiator module.
Unplug the connector of the fan. Remove the screws around the CPU.
Take out the CPU, wipe out the dust and remained silica gel.
And so done the radiator module.
Smear new gel.
Smooth it thin and even.
We’ve finished the cleaning.
Isn’t it simple？