Have you tried removing power from the unit for an hour or so, to see if it will reset?
I have tried to find a pinout for the keypad for you but so far have not had any success. You really need that so the keypad can be checked with a meter to confirm that you have a stuck key.
Here is a tech sheet which may be of some use.
https://www.servicematters.com/docs/...%208051291.pdf