Fixing the hourly chimes on a smith westminster clock?

i have just bought a smiths westminster chiming clock with a movement stamped k6a. The clock ran fine when it
was first set up but now only strikes once on the hour . It keeps good time and completes the full chime sequence on each 15 minute sequence. I have let the clock fully wind down and used the chime on and off lever but it still performs one only strike on the hour. I think the clock was made in 1955 and its in good condition.