A description is given of a personal computer implementation of an expert system for the diagnosis of electronic equipment. The expert system employs mixed mode reasoning. It reasons from first principles using a device specific hierarchical structural model and is guided by a universal trouble-shooting control strategy, and heuristics. The structure of an analog or digital electronic device is viewed as a hierarchical interconnection of modules and is represented as a semantic network. A reduced behavioral description records the normal expected behavior. It is not used for simulation, thus saving computer power. A structure analyzer sub-system processes the semantic network to infer topological relationships and performs signal propagation. During execution the expert system cycles through the three major steps of trouble-shooting: candidate selection, checkpoint recommendation, and inference.
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