One reason is that the position of the inserted column under the key cap is offset, which makes the key cap and the shell of the key body stuck together and unable to bounce up, resulting in key jam (this reason mostly occurs on new keyboards or keyboards that have not been used for a long time).

Another reason is that the button is used for a long time, the elasticity of the return spring becomes worse, and the friction between the elastic sheet and the push rod becomes larger, which can not make the button bounce up, resulting in the button being stuck. This reason mostly occurs on keyboards that have been used for a long time.

When the keyboard is stuck:

You can take off the keycap and press the button. If the pressure bar is not elastic or weak, it is caused by the second reason, otherwise it is caused by the first reason. If the keycap is stuck to the shell of the key body, a washer can be placed between the keycap and the key body. The washer can be made of slightly hard plastic (such as discarded floppy disk sleeve), and its size is equal to or slightly larger than that of the key body. Open a square hole at the position where the push rod passes, so that the ammonium rod can pass freely. Insert the keycap after putting it on the push rod. Using this gasket to prevent the key cap from sticking to the key body, the faulty key can be repaired; If the spring is tired and the resistance of the elastic sheet becomes greater, you can open the key body and slightly stretch the return spring to restore its elasticity. Remove the elastic sheet to restore the key body. By removing the elastic piece, the resistance of pressing the lever is reduced, so that the faulty key can be restored.