In described examples, a time-domain analyzer is arranged to generate an indication of a number of high-frequency events of an electrical monitor signal that includes a fundamental periodic frequency. The high-frequency events include frequencies higher than the fundamental periodic frequency. A frequency-domain analyzer is arranged to generate frequency band information in response to frequencies of the electrical monitor signal that are higher than the fundamental periodic frequency. A fault detector is arranged to monitor the indication of the number of high-frequency events and the generated frequency band information, and to generate a fault flag in response to the monitored indication of the number of high-frequency events and the generated frequency band information.