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It is a simple fix but it may take more than one try to get it correct. you should not try to correct it your self unless you have some experience tinkering with clocks. on the front of the clock in the center the minute wheel fits on the center stem, on the backside of this wheel are 2 small pins that are 180 degrees apart these pins are not equidistant from the center in other words 1 pin is closer to the center than the other, the pin that is closest to the center is the half hour accuateing pin if this pin is bent down it will strike late if it is bent up it will strike early. check to see if the pins are perpendicular to the back surface of the minute wheel. if you feel that they are not correct and you want to try to adjust them do it very carefully. also check to see that the pin makes proper contact with the strike lifting lever. let me know if it works out. :)