Abstract. There have been some Artificial Intelligence applications developed for electronic circuits diagnosis, but much remains to be done in this field, above all in the analog domain. The purpose of this paper is not to give a general solution, but to contribute with a new methodology. Our aim is to develop a methodology for analog circuit diagnosis based on improving the well-known fault dictionary techniques by means of new cases addition or adaptation towards a Case Based Reasoning system. As an example, a fault dictionary method have been studied in detail. It has been used as starting point for case base construction to be applied to a real electronic circuit. The faults considered are parametric, permanent, independent and simple.