How do I correct our grandfather from clock chiming the wrong time?

My girlfriend has a grandfather clock, I do not know the name or brand. I know that it was built after 1960. We have never experience problems until recent.
The problem we have encounter is now instead of the clock chiming at the hour, it chims the proceding hour.
meaning if it's 12:00 the clock will chim 1:00 or at 2:00 it will chim for 3:00 and so on... the quarter and half and 3/4 hour chims are working properly.