STI was already testing the empty PC boards with a "bed of nails" tester; they had reasonable confidence that the PC boards themselves were not likely to be a problem. The problem was that the assembled PC boards were operated as slave devices when commanded from a master controller over an RS-485 serial interface. STI needed an intelligent tester that could emulate the master controller to exercise the PCBs under test and ensure that all of its features were working.

SEI proposed the development of a low cost test system using mostly off-the-shelf components and a standard PC running Windows 95. The PC interfaces via RS-232C to a test unit enclosure which contains the test instrumentation and interface electronics. Above the electronics test unit is mounted a SEMCO mechanical test fixture that has been customized for probing a control head PC board. The test fixture tests one control head PC board at a time.

STI purchased the proposed test system. Although SEI had quoted them delivery in 90 days, we actually delivered the completed system (hardware and software) to them in about 7 weeks. Since delivering the test system late December 1997, STI has tested hundreds of control head circuit boards using this system. We have had no complaints or problems reported regarding this system to date (April 1998).