That machine probably has a Variable Frequency Drive motor and controller. The Controller is what "converts" the frequency. It is most likely proprietary as most of these units are for consumer machines. The Controller takes in an input voltage(120V, or 240V 60HZ), Rectifys the supply, steps up the voltage, uses IGBT's and processors to "chop" the supply into a varying high frequency. Adds two other supply lines, spaces the current 120* apart per supply line, Internal frequency can range from 6KHz to 8KHz. Went voltage, and current supplied to the motor are constant, the Frequency is what determines the speed. So, the output supply can range from 120V 60HZ Modified Sine wave to 240V 400HZ. Both the motor and the controller may have to be replaced if they are faulty. Be sure to check ALL connections. A shorted motor, or one of too high resistance on the windings can cause the controller to fail. Also the controller itself could have faulty electroincs. Since both the motor and the controller are proprietary to this brand it will cost you some BIG ones to replace them. That's why Decent VFD's use 3 phase as the input voltage, and not 120V or 240V 1 phase.
Good luck!!