A method for magnetic/impedance burst testing of large electric motors to determine broken rotor bar defect. The method providing a portable tester and includes a Signal Processor, a single-phase power source VAC, an AC/DC boost converter connected to the power source, at least one energy storage device connected to the AC to DC boost converter, a Pulse Width Modulated drive module (PWM) connected to the at least one energy storage device, and a series of at least three switches (IPM) using switch/level boost-type PWM rectification. The burst test is repeated until a full rotation of magnetic angles are tested and recorded with the Signal Processor. Rotor impedance versus magnetic angle of the full rotation is verified in order to check for failure, and broken rotor bar defect is determined when a shift in measured stator's impedance/admittance level for any of the given magnetic angles is identified by the Signal Processor.