Well, you are right, an F2 error code does indicate a problem (usually a stuck key) with the interface board. Make sure the ribbon cable connectors are clean and dry. Make sure that there isn't anything at the bottom of the cable socket that might be shorting out 1 or more connectors. If you can't find anything wrong, the procedure is to replace the user interface first, and then if that doesn't work, replace the main controller. (Yes, I know, that can get expensive.)
Answers & Comments
Well, you are right, an F2 error code does indicate a problem (usually a stuck key) with the interface board. Make sure the ribbon cable connectors are clean and dry. Make sure that there isn't anything at the bottom of the cable socket that might be shorting out 1 or more connectors. If you can't find anything wrong, the procedure is to replace the user interface first, and then if that doesn't work, replace the main controller. (Yes, I know, that can get expensive.)