Functional test is not the place you want to be confronted with component failures on your PCB. Ideally, all defective components should have been detected and replaced in a prior test process.
Isolating and diagnosing failures that escape an in-process test are very costly and time-consuming when you have to find them at functional test. By definition, functional test programs are not designed to uncover defective components. Their main purpose is to test all of the functions of the unit-under-test (UUT) under normal operating conditions.
In actuality, we all know that component failures do appear at functional test. And they must be found and repaired. To help users of HP 3079CT Communications Test Systems to diagnose these failures, Hewlett-Packard has introduced Fault Detective.
The HP 3079CT is a telecommunications functional board test system that tests all access-loop products including plain old telephone service (POTS), integrated services digital network (ISDN), pair gain and hybrid fiber coax (HFC). As part of the HP 3079CT, Fault Detective helps isolate board faults on communications products at functional test.
Unlike other technologies, Fault Detective models the interaction of the existing test suites and the UUT. It uses algorithms to analyze the pass/fail information gathered at functional test to generate a clear diagnosis of the failure to the component level. HP Fault Detective does not require additional test equipment or complex programming.
To create a model, you describe the tests performed and the devices exercised by each test. An integrated Debug Advisor helps you fine tune the performance of the model. After you have created all models for the board, add them to the functional test suite. Fault diagnosis is now part of your test program. Fault Detective also has the capability to find areas of low test coverage and provide feedback to improve the overall test program.
On one product, HP reports that Fault Detective has achieved a fault diagnosis accuracy of 70% and enabled the company to reduce the number of diagnostics technicians from 10 to 3. The net result is an overall savings of $100,000/month. Hewlett-Packard, (800) 452-4844.
Copyright 1996 Nelson Publishing Inc.
November 1996