Packaging Requirements ents for Optimized Malfunction Isolation by Systematic Substitution

This paper describes a malfunction isolation technique which is applicable, primarily, to electronic systems. The technique is effective for essentially 100 percent of all failures, including multiple,terintermittent, interconnection, and closed-loop failures, to the discard-at-failure (DAF) hardware level. The value of the technique, in addition to its simplicity and ease of use, is that, in very complex systems, it virtually eliminates the requirement for complex procedures, high personnel skill levels, and manual test equipment necessary for malfunction ion isolation. The sine qua non of the technique is the packaging of the equipment. Each level of hardware must contain approximately four plug-in packages per package. Malfunction isolation is accomplished by substitution of packages in the top level, one at a time, until the defect is corrected. Next, the second-level packages in the defective top unit are replaced, one at a time, until the bad package at this level has been identified. The packages are substituted in each subsequent level until the DAF item is reached. When an equipment is packaged according to this technique, the average number of substitutions required to isolate to a single malfunctioned DAF item is approximately 1.8 times the natural logarithm of the number of DAF items in the system. For example, a system containing 4100 DAF items requires about 15 substitutions to locate a single defective item. The foregoing is true when no information is available regarding the best sequence of exchange. If such information is available, the number of substitutions will be reduced.