Hi,

Depending on the environment these are being used in, sometimes the switches could get clogged up and need some cleaning/spraying. When you open the keyboard up and remove the top panel, the switches reside below the hard black plastic that holds the buttons... these come off with a slight tug. You may then spray a cleaner (licenced for electronic circuit boards) to take off any dust particles that might be within the contacts).

Hope this helps.

Thanks,

AJ