Automated continuity tester for large wire-wrapped avionics chassis

In the 1960s and 70s wire wrap circuit construction was very common in electronics manufacturing. Although, its use has fallen out of favor in manufacturing due to surfacemount technology along with high-quality, rapid, and inexpensive professional printed circuit board production, it is still useful for prototyping. As one might imagine, manually testing the continuity of a large, complex wire-wrapped assembly is not only time consuming, but also highly error prone. An example of a sophisticated, but older and extended-lifetime avionics system is the AN/ALQ-161 Defensive Avionics System on the B-1B. Each LRU chassis has a unique wire wrap connectivity scheme. Because of the complexity of the connectivity nets and the fact that each LRU´s net list is unique, manual testing was considered unreliable and excessively time consuming for the reasons already mentioned. We present here the system design of an automated chassis wiring tester, emphasizing continuity testing.