while there are many 'tricks' for when a scope is not available, the "running blinnd" is still, at best, cumbersome.

"the pulse at pin X looks like this" is 1000 times better than "I think there is a pulse at pin X"

I do not think I'm the only one that on a non-technical visit (bringing no instruments) have been asked "now you are here can you have a look at this" and, in some cases I have been succesful. NOTE "in some cases", there are many cases that can not be solved in a reasonable time without proper instrumentation.

Now on a totally different track, I recall an incident in the old minicomputer/TTL days when a brit I consider smarter than myself and yours truly spent more than a month hunting an intermittent which turned out to be a pulse too narrow for the scope of the day to show and we had to resort to the "DNA scope" (loop: reasoning what it COULD be, trying it, back to loop:). We finally, by sheer reasoning, found that when chip x was in the high side of the range, but still within the parameters, under certain circumstances a ~2ns pulse could slip through and the equipmenta would fail ~once a day.

so, yes a scope is essential, but, if you have a month, you can, probably, reason your way to the cause of theproblem.

Erik