Abstract: This study illustrates a method of fault diagnosis of analog circuits with feedback. In this study an efficient single catastrophic fault detection and identification approach for analog circuits is described using hierarchal testability procedure. The Simulation Before Test (SBT) method of fault diagnosis is used. The Circuit Under Test (CUT) is excited and output parameters are observed. The fault dictionary is developed for the CUT. Based on the deviation of the present response from fault free, fault detection and identification is done. The presented testing approach is applied on an analog benchmark circuit to validate the testing approach.