A method and apparatus are provided for identifying one of a plurality of operational modes of a monitored video cassette recorder (VCR). A sensor is positioned near the monitored VCR for detecting a radiated signal of the monitored VCR. The detected signal is appplied to a filter for filtering the detected signal and for providing a plurality of predetermined band-pass filtered signals. A neural network is used for processing the plurality of predetermined band-pass filtered signals to identify the operational mode of the VCR.

An artificial intelligence based method and apparatus for locating faults in electronic units includes a technique for modelling electronic units in terms of behavioral constraints. Behavioral constraints model circuit components in terms of changes in outputs thereof which result from changes in inputs thereto. These changes, referred to as "phase changes" may be supplemented by gain and compliance constraints to model an electronic unit at all functional abstraction or hierarchical decomposition levels thereof. In addition to providing a universal modelling scheme, behavioral constraint relationships provide a highly accurate indication of subtle changes in a circuit, for accurate fault location or troubleshooting. Troubleshooting takes place by applying a predetermined search strategy on the electronic unit which is represented by behavioral constraints. The search strategy begins with a top down search. When a faulty block is found, the search moves down one functional abstraction level and searches the next lower level block having an output corresponding to the output of the higher level block. If the next lower level block is not defective, adjacent blocks at the next lower level are searched. Testing of the electronic unit is begun according to the functional test plan specified for the unit. Each functional test in the functional test plan is associated with one or more blocks at a functional abstraction level. When a functional test fails, troubleshooting begins at the block and functional abstraction level corresponding to the failed functional test.