Failures associate with bad hand pieces and blade failures in an ultrasonic surgical system are distinguished by monitoring the rate of change of the resonance frequency and the rate of change of the resonance impedance of the hand piece/blade as the drive frequency is changed. As the system reaches resonance, the control system locks onto the resonance frequency. When a loss of lock occurs with no recovery, the rate of change of the frequency and rate of change of the impedance are compared to obtain the fastest rate of change which is stored in non-volatile memory of the ultrasonic generator. If the rates of change are higher than normal rates of change due to temperature changes with the longest blades, a "Bad Blade" message is displayed on an LCD.