It's definitely eeprom; it's corrupted in the masked areas as well as
the parameters you were able to adjust. Reflashing the prom with CC
is the best way to fix this and other problems in the eeprom you may
not know about. The other way is to hot swap the prom when using a
prom with the CC function. There is a procedure on this ngs FAQ about
restoring audio, but the idea is the same.

John