Equivalence amongst the single and double catastrophic component faults of a potentiometric DAC under steadystate d. c. conditions is investigated. Easily identi3able equivalent faults are shown to populate the fault list in significant numbers. By facilitating a systematic testdesign approach focused on the prevention of equivalent fault conditions during test, equivalent fault analysis is used to greatly increase the percentage of catastrophic component faults diagnosable with a Built-In Self-Test (BIST) in [13]. The efect on analysis of component tolerances and other nonidealities is yet to be considered.