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August 09, 2011

Comments

John Dunn

For those who might not know, the Harris' Theorem to which I refer is not that for "asymptotic coupling" or any similar issue but comes instead from QST magazine published by the ARRL and states (paraphrased):

Any dropped tool will always land where it can do the most damage.

Alex Iwanow

As a young 1970s engineer, I designed a circuit with several dozen components and was preparing a production run of 100. Since the PCBs were part of a medical device, I had plans to pre-assembly-test 10/1000 of each component, even though I had purchased 100% "vendor pre-tested-burned-in" components. My boss complained the tests we redundant.
I felt great but uneasy. As my boss looked over my shoulder, the very first part failed - a 1N914A diode had reversed marking band! Needless to say I tested all 1000 diodes and still made the deadline delivery that evening.

A lesson learned early that re-occurred several times in my career.

Alex Iwanow

Michael Alderete

Hah!! no further comment

William Ketel

The unfortunate reality is that testing or measuring will always be required for any process that is not "100% controlled", meaning that checking is needed if there is not 100% certainty that the results will be exactly as desired.
As for the issue with the terminal strips, I would never ever trust any supply area to have every single part both correctly placed and be the correct part for that place. And any assembly that must work the first time must always have all parts checked prior to assembly. That actually is good economics, which is to catch faults before to much value is added.

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