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T420 Keyboard faults

2019-06-03, 17:30 PM



So today, I decided to replace the thermal paste on my CPU as I was noticing the idle temps were pushing 55-60C 


After completing the task, I endeavoured to test the system before completely putting the fascia and back screws in. 


When I did so, I was able to boot up, login, test programs, etc.


When I put the fascia and the back screws back in and booted up, the keyboard no longer worked.


The caps lock key during boot up flashes as per normal, but doesn’t operate. The delete key doesn’t work either. I won’t specify every single key that doesn’t work, as there are numerous and it’s varied to its location. 


To check if if perhaps I screwed something into it I took it all apart and removed the keyboard. I checked the cable, the contacts and checked the reverse side of the board for any cracks or imperfections.


None could be found.


I presume that this will need to be replaced but money is a little tight at the moment and I truly hope it’s something very silly like corrupt drivers or something


Thanks in advanced!


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Re: T420 Keyboard faults

2019-06-03, 18:19 PM

There is no driver.  The only thing I can imagine you could have done wrong is to put the screws back into the wrong places.  The 4 screws that hold the keyboard bezel are 15mm long, while the screw in the center (keyboard) is 10mm.  Too long of a screw in the center hole will damage the keyboard near the area where the cable attaches and the electronics are.  T420 uses the same keyboard as 400/500 and 410/510 machines, but 430 /530 are different.


The best keyboard tester I have found is here:  (free)





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