Abstract: In order to simplify the hard work for the fault location in the fault diagnosis of analog linear circuit a procedure for determining the existent range of fault elements is presented;i.e. by assuming the quite realistic k-fault hypothesis,a group of elements that represent all the circuit elements and give a unique solution for the fault diagnosis equations under the k-fault hypothesis is determined.This group is called an optimum set of testable elements.Therefore the work for fault location can only operate in the elements of this group and does not need to perform in all the circuit elements.So the method constitutes the first step in the development of whatever procedure for the fault location of analog linear circuits.The proposed procedure is based on the testability evaluation of the circuit and on the determination of the canonical ambiguity groups and has its theoretical foundation in testability concept and in the canonical ambiguity group concept.The testability evaluation can be deduced by referring to fault diagnosis techniques of the parametric kind.

Key words: analog linear circuits, testability, ambiguity group, fault location, parameter fault diagnosis