You did what?

Staff -- Test & Measurement World, 7/1/2001

No scraps allowed
We successfully developed four or five test programs on our new rack-and-stack test system and were ready for a new challenge. But on the next board type we had to test, the high-impedance thermocouple channels proved troublesome. The program development went smoothly until we started to debug the thermocouple channels. These channels all produced short-circuit readings.

None of our usual debugging tricks could isolate the problem. The board worked fine in a bench test that connected the thermocouple channels to millivolt sources. The thermocouple inputs even worked properly when we manually pressed the board’s connector pins onto the bed-of-nails. But under normal test conditions, the problem reappeared. That observation led to the source of the problem. In the test fixture, our mechanical engineer had used scraps of electrically conductive static mat to cushion the board’s connectors.—Jon Kennedy, Foxboro, MA.

Fussy about fuses
Years ago when I worked at Scientific Data Systems, the company had a policy of inspecting and testing all incoming components. We had hired a new test engineer, and as part of his training, we asked him to devise a test for fuses. He came up with a test jig that used a standard Simpson 260 VOM to perform a continuity test on the fuses. The test setup worked quite well for high-current fuses—those greater than 1 A. But all of the small-current fuses failed the continuity test 100% of the time. Eventually, the new engineer figured out that the 260 VOM supplied a 1-A current when set on its 1-W range.—Jon Turino, Beaverton, OR.