Attacking "bad actor" and "no fault found" electronic boxes

A the percentage of what are termed "bad actor" and no fault found (NFF) electronic box in military weapon systems is steadily growing. These are boxes that fail during operation, but test NFF during back shop testing, or, that fail during back shop testing and then test NFF at the depot repair facility. During operation, an electronic box is stressed by various environmental conditions which are normally absent on a test bench. If there are cold or cracked solder joints, corroded or dirty connector contacts, loose crimp joints, hairline cracks in a ribbon cable trace, or other intermittent conditions, the intermittency can occur while the box is under stress conditions, yet seldom occur while the box is on a test bench at room temperature. Very little concerted effort is currently focused on detecting, isolating and repairing these intermittent problems. Virtually all testing activity simply tests the unit for normal operation, one function, one circuit, or one set of circuits at a time. If an intermittent circuit is not displaying its intermittent nature at the instant it is being tested, the intermittency remains undetected. A three-pronged effort is currently underway to attack and repair bad actor and NFF electronic boxes. The first is to collect detailed repair data to identify which boxes are bad actor and NFF units. The second is to collect test data to determine which units yield inconsistent test results between back shop testing and depot testing, and why. The third is to employ a system that detects and isolates electronic box intermittent circuits. This paper describes the success realized to date by employing each of the three techniques described above, and how they are now effectively being employed together to reduce maintenance costs and improve avionics reliability for the F-16 weapon system.