which equipments are being tested and also which equipments are in an out-of-tolerance condition. A
printer provides a read out copy of the test results. These results are used by maintenance personnel to
isolate the fault in a removable assembly to a replaceable part.
Centralized Automatic Test System (CATS)
CATS is an on-line system that continuously monitors the performance of electronic systems,
predicts system performance trends, and isolates faults to removable assemblies. CATS, however, is
computer controlled and the instructions are preprogrammed in the computer memory. The status of the
electronic system being monitored by CATS is presented in various forms. Information concerning a
failed module is presented on a status- and fault-isolation indicator to alert the maintenance technician of
the need for a replacement module. If equipment design does not permit module replacement, complete
electrical schematics and fault-isolation procedures will be made available to the maintenance technician.
OFF-LINE TEST EQUIPMENT
The Navy has under development an advanced assembly tester designated Naval Electronics
Laboratory Assembly Tester (NELAT). This tester is an off-line, general-purpose test system designed to
check-out and isolate faults in electronic plug-in assemblies, modules, and printed circuit boards.
Equipped with a complete range of instrumentation, the system allows testing to be accomplished
automatically, semiautomatically, or manually. In the automatic mode, a complete range of stimuli
generators and monitors are connected and switched by means of a microfilmed test program.
The NELAT incorporates modular electronic assemblies that will facilitate updating of the system.
The system is designed for use aboard ship. When put into service, this tester will greatly improve the
technician's capability in the checkout and fault isolation of microelectronic assemblies.
Another important system for off-line testing is the Versatile Avionic Shop Test System (VAST).
VAST is used in the aviation community for fault isolation in aviation electronics (avionics) equipment
on ships and shore commands with aircraft INTERMEDIATE MAINTENANCE DEPARTMENTS
(AIMDs). It is an automatic, high-speed, computer controlled, general-purpose test set that will isolate
faults to the component level.
GENERAL-PURPOSE ELECTRONIC TEST EQUIPMENT (GPETE)
When no automatic means of accomplishing fault isolation is available, general-purpose electronic
test equipment and good troubleshooting procedures is used; however, such fault diagnosis should be
attempted only by experienced technicians. Misuse of electrical probes and test equipment may
permanently damage boards or microelectronic devices attached to them. The proximity of leads to one
another and the effects of interconnecting the wiring make the testing of boards extremely difficult; these
factors also make drift or current leakage measurements practically impossible.
Boards that have been conformally coated are difficult to probe because the coating is often too thick
to penetrate for a good electrical contact. These boards must be removed for electrical probe testing.
Many boards, however, are designed with test points that can be monitored either with special test sets or
general-purpose test equipment. Another method of obtaining access to a greater number of test points is
to use extender cards or cables. The use of extender cards or cables makes these test points easier to
Special care should be exercised when probing integrated circuits; they are easily damaged by
excessive voltages or currents, and component leads may be physically damaged. Precautions concerning
the use of test equipment for troubleshooting equipments containing integrated circuits are similar to