Cost-Reduced M587 Electronic Time Fuze: Root Cause Analysis of July 1979 Early Bursts

摘要

The Root Cause Analysis effort directed at explaining the two early bursts noted during the July 1979 validation test of a cost-reduced design for the M587 electronic time fuze has been completed. This cost-reduced fuze design contains three integrated circuits and one printed-circuit board. The early burst was identified as having resulted from the poor quality of the cost-reduced interface and firing circuit (IAFC) hybrid integrated circuit (IC). Detachment of the 820-pF capacitor during gunfire, coupled with an intermittent wire bond (which opens during setback and then closes again) can defeat the initialization circuit and preclude proper generation of the short and long pulses needed to establish the starting count of the timer IC. In the absence of these pulses, the timer has a strong tendency to initialize at about 257 counts (26 s). Corrective actions are now being defined not only to improve the quality of these connections but also to assure that this combination of faults cannot result in an unsafe fuze. Other weaknesses in the cost-reduced design, not believed to be related to the early burst, were identified and corrective actions defined. It was determined that a life combination of faults in the current production design would cause the counter to initialize at about 1790 counts (179 s), which, for all practical missions, would be a safe fail-long condition. (The current design contains four integrated circuits and two printed circuit-boards). (Author)