Hi Daniel:
Thanks for the quick response. I am unsure I can tell you anything immediately that will be of use.... Normal functionality is (in slightly simplified form):
a) 8 LEDs are normally off.
b) The board monitors the state of the inductive sensor.
c) When inductive sensor pulses on, LEDs perform a motion pattern and then go off.
In problem state, on board bootup, the two "end" LEDs (they are linearly arranged) are on (they should be off), the rest off, and (I am 90% sure) signals to inductive sensor are ignored. [The current problem board is offsite in a nature center, so I can't test it, which is why I am sounding vague. I will be getting it back and thereafter can perform more tests.]
Can you suggest the kinds of things I might measure/try? I have a digital storage oscilloscope, multimeter, spark generator, variable voltage power supply, STK500 programmer, etc., and so can try whatever tests might be of use. Also, would it be worth trying some kind of "program lock" after we program things (via the fuses maybe ? I am only just getting familiar with your system) that would reduce the chance of this kind of thing in the field?
And finally, the problem has been sporadic enough that I don't have a complete pattern on any front (e.g., were the boards partially damaged somehow before installation, are the symptoms really always identical, etc.). I wanted to post now, even without all this information, because without some idea of what to look for, given how intermittent the problem is, it may take me years to debug...
David