It should be clarified to what the term "broken" applies: Are you missing blades? Are you missing any full section? If this is the case and the missing one is important you can unbalance the turbine and do not let it reach the corresponding revolutions. In this case you must replace the turbine. On the other hand, one of the causes that may be missing revolutions in its low capacitor or the motor winding is damaged or the bushings are pasted or broken. To solve the first you should change the capacitor, for the other two, change the motor.