ThinkPad T420 Keyboard Replacement

Introduction

If your Lenovo T420 has keyboard or thermal issues, this guide will show you how to replace the keyboard and gain partial fan access.

Guide notes

If you are removing the keyboard for fan access, being too close or using too much air can damage the fan. If the damage is particularly severe the system will give you a fan error and shut off to protect the processor (and dGPU, if equipped). If the system says Fan error when it is rebooted, the fan is damaged and will need to be replaced in order for the system to boot. Use caution if you suspect the fan is failing prior to cleaning the heatsink. The fan in the author's system was rattling before cleaning and it has not happened since. If the fan ends up getting damaged, this is NOT your fault; all you did was reveal a hidden failure.
If you are replacing the keyboard, check the Lenovo HMM to determine what keyboard you need. This can also be found on the back of your old keyboard as well. I am not referencing a part because every country uses a different FRU.
While this is not a hard repair, you may wish to sort your screws. Multiple screw types are used.
Watch the ground on the chassis by the RAM door, especially if it has been serviced before. This can get in the way or come loose from the chassis. If this happens push it back into place. It will eventually come out again, so the only cure is to replace the lower chassis.

If the label on the back of the keyboard is not worn, that can be used to reference which keyboard is needed.
IMPORTANT: Each country has a different keyboard FRU part number. To match the keyboard you have and which one you need to purchase, check the back label or refer to the Lenovo HMM.

If completing a step like a clone of your old hard drive/SSD, DO NOT remove the battery until the process is complete!
Unlock the latch locking the battery in the laptop.
NOTE: To remove the battery, the tab must be held in to avoid having the lock reinitiate inside the laptop.

After unlocking the battery, remove the battery from the reverse way it is installed to remove it from the laptop.

EET owners: Your kit has this bit. No purchase needed.
If you are removing this cover to upgrade/replace your lower RAM module, the keyboard screw DOES NOT need to be removed.
WWAN ready systems ship with antenna covers over these cables. Someone installed a WLAN card in this T420 which disabled the better card and was removed.
Loosen the screw in red (Phillips #2). This screw stays captive in the bottom RAM door cover, and does not need to be removed.
Pull the cover up with a fingernail or a nonmarring pry tool.
Remove the screw retaining the keyboard.

To reinstall the keyboard, refer to the steps in this guide.
This step can be skipped if you remove the keyboard to upgrade/replace the RAM. However, disconnecting it may allow for better access to the upper (Keyboard) RAM module.
If you have a can of compressed air available, some of the dust can be removed at this point. Further disassembly is required for a full cleaning.
Disconnect the keyboard from the motherboard. Use a plastic pry tool for this step.