An Automatic Self-Checking and Fault-Locating Method

A method is described for designing systems which automatically check themselves and give indications by which internal faults can be located quickly and accurately. Relatively little circuitry is required, and the performance of the test and fault location are easy. The proposed method entails the arrangement of a sequence of events which can be completed properly only if no malfunction exists. Applied to a 555-transistor digital system, the method yielded the following results: An indicator-light test and a 2.27-second self-check provide 100 per cent confidence that the device is in perfect order. 90 per cent of the trouble indications isolate faults to one or two plug-in cards, each holding one to six transistor circuits. This checking capability is provided by only 182. per cent of the transistors in the system.