This paper demonstrates a novel technique based on the use of a fuzzy logic system and the simulation before test (SBT) approach for hard faults detection and localization in analog electronic circuits comprising bipolar transistors. For this purpose, first, simulations of the circuit under test (CUT) are performed before the test stage by investigating the response of the circuit under test in faulty and fault-free conditions. Following this, two signatures parameters—output voltage and supply current—are observed and used for the fault diagnosis; the CUT is simulated using the OrCAD/PSpice software, and the output is analyzed in the DC domain. This method is validated through an inverter amplifier based on the uA741 operational amplifier. Then the results of different experiments are presented to demonstrate the applicability of the proposed method by increasing its efficiency.