This thesis describes a methodology, a representation, and an implementated program for troubleshooting digital circuit boards at roughly the level of expertise one might expect in a human novice. Existing methods for model-based troubleshooting have not scaled up to deal with complex circuits, in part because traditional circuit models do not explicitly represent aspects of the device that troubleshooters would consider important. For complex devices the model of the target device should be constructed with the goal of troubleshooting explicitly in mind. Artificial intelligence, automated diagnosis, hardware troubleshooting, model-based reasoning, diagnosis from first principles, temporal reasoning.