The scope of the present work is focused in the use of Belief Bayesian Nets (BBN) in order to model complex electronic system failures with hardware and built-in software. The theory of Bayesian networks can be thought as a fusion of influence diagrams and Bayes Theorem. The present analysis emphasizes their use in replacement of the conventional Fault Tree Analysis (FTA). A later study of software necessary to implement their application completes the proposed objective.Sección: Diseño de hardware FPGACentro de Técnicas Analógico-Digitales