Hello, I have a Dell 15R-5521, with the problem that the Ctrl, Alt, Shitf and Num Lock keys do not work, I tested the keyboard with a keyboard tester and it is functional, I also got another new keyboard and the computer has the same problem with the same keys. Check continuity between the ZIF connector from the keyboard to the KBC and all pins are correct. I cleaned the ZIF connector and the KBC and I still have the same problem. I reinstalled windows just in case, and it didn't work. I updated the BIOS to the latest version A16 and there were no changes.

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Hola, mi nombre es Mauricio, tengo un pequeño taller de reparaciones, me encanta aprender cosas nuevas y también contribuir.