Experience with an expert diagnostic system shell

Efficient diagnosis and repair of failing electronic circuit boards is essential for a major telecommunications company, such as British Telecom. This is particularly true of complex high volume cards found in the new digital exchanges. Some boards comprise mixed analogue and digital circuitry and technologically advanced components such as Subscriber Line Interface Circuits. As such, they are not amenable to the well-established back-tracing diagnostic techniques developed for purely digital circuitry. The traditional approach to diagnosis, that of deploying technicians armed with `rack and stack´ equipment, is costly in terms of manpower and equipment, and is critically dependent on the availability of skilled labour. The goal of the work described in this paper was to achieve a substantial cost reduction in the diagnosis of mixed signal boards