FAULT ISOLATION

Subsystems tests are functionally grouped and mode oriented so that related functions can be chal- lenged using the same setup, procedures, and stimuli. Where practical, subsystems tests use tactical indi- cators for measurement, leaving the requirement for special hookups and test equipment to equipment- level testing. A major combat ship contains most, or all, of the following subsystems: 1. 2. 3. 4. 5. 6. Search-radar subsystem Command and control subsystem Countermeasure subsystem Gun/missile weapon subsystem External communications subsystem Navigation subsystem Equipment Testing Equipment testing is defined as testing that is generally directed toward power levels, frequencies, servos, special features, and output functions. The PMS may require special external stimulating equip- ment and special- or general-purpose test equipment for testing measurements. FAULT ISOLATION The objective of fault isolation is the systematic application of fault-isolation tools needed to isolate the exact unit or fictional interface responsible for a fault or degraded operation during testing or tactical operation. To diagnose and effect timely repair of faults within a fire-control system, you must fully understand fault-isolation concepts, the fault-isolation tools available to you, and the capabilities and limita- tions of those tools when applied to system fault iso- lation. 3. It conveys the maximum intelligence regard- ing the source of the fault. 1-6 Although the primary entry into fault isolation is from test-detected faults, improper operating condi- tions can be observed during tactical operations, including operator awareness, data extraction and re- duction, and on-line monitoring. Fault isolation leads to corrective maintenance. After a fault has been isolated to a specific unit or interface, corrective action in the form of repair, re- placement, and/or alignment must be taken. The corrective maintenance performed may or may not be required to return the system to an operable condition. There may have been more than one fault contributing to the out-of-tolerance condition that initiated the fault-isolation process. The possibility of faulty re- placement parts and incorrect adjustment or alignment exists. Instead of solving the problem, corrective maintenance may have added to it. Therefore, it is mandatory that each corrective action be followed by verification. Normally, verification is accomplished by re- creating the test environment and rechallenging the function. Where alignments are concerned, the inter- dependent effect upon other elements of the combat systems must be considered in the verification pro- cess. FAULT-ISOLATION TOOLS During testing or operational use of a weapons system, faults can occur in the interface between sub- systems, in the interface between equipments of a subsystem, or in the equipment itself. Rapid fault iso- lation requires decisive action in selecting and imple- menting the most appropriate fault-isolation tools. A fault-isolation tool has the following three character- istics: 1. It requires the least amount of time, equip- ment, or service. 2. It is easily implemented.