Scantronic 9450 keypad issue?

My old but very realible Scantronic 9450 as a issue where some of the keys on the pad dont now function.
My tv remote does this at times but i take it apart and clean and it works.
Is this something that can be done to the keypad?
Just to check,if i open the 9450 case by the single screw,the tamper will sound if i recall,does my entry code stop this? i am sure i have opened the case to wall paper behind it. would hate to open it and not be able to stop the thing.