Repair actions for self-diagnostic machines

The author develops a model to estimate the average number of repair actions (RA) for a system that is divided into two parts: the functional circuits that execute the operations required by the objectives of the system, and a part that performs error detection and diagnostic functions. The breakdown of a functional circuit (FC) generates a repair action but the failure of a maintenance circuit (MC) is only observable through FC failures. On the other hand, MC breakdowns may cause an incorrect diagnosis or fault isolation, and several repair actions may therefore be required to restore the operation of the system. The failures of the circuits come from either defective chips that have not been detected during manufacturing and testing or time-dependent breakdowns of the circuits that occur after the installation of the system. The author shows that similar formulas can be used in both estimations. The expected number of defective (failed) functional chips is inflated by the probability that there might be defective (failed) maintenance circuits in the system