Motor drive diagnostic and control methods and apparatus are provided in which rectifier and inverter switching devices are individually monitored for malfunctions, and detected malfunctions initiate implementation of a safety function to signal a drive controller to shut down non-safety-related processing, to discontinue command pulse signaling to the switching devices, and to disable optical transmitters between the drive controller and the rectifier and inverter switches, and an input contactor or other switching circuit is opened to disconnect input power from the motor drive after implementation of the safety function.