Bill Kuncicky wrote:

>Thanks for all the replies.  Everything seems to be working OK now.  Since I
>did everything that people suggested (100 nanofarad caps across Vdd and Vss
>close to the PIC pins, carefully checked for any intermittant shorts, and
>put huskier caps on the 7805 and checked the output with the scope) it is
>hard to say just exactly what did the trick.  Assuming the trick is did, of
>course.  From what everyone has said there is no way that anything that I
>did can hurt, though, in any case.
>
>I have to say that I am amazed to learn that the caps on the regulator
>(input to ground and output to ground) can be that large!  I have always
>assumed that the specs of the manufacturer had to be followed pretty
>closely!  Live and learn.  That is, IMHO, a Good Thing To Know!  I shall
>file it with my many other Good Things To Know.
>
>I also noticed that Bob Axtell said that the symptoms were "absolutely
>classic" for the problem being oscillation, and Spero Pefhany has the
>opinion that it sounds like something else (latchup, or intermittent short
>of an output to supply rail.  So two of the experts disagree.  :-)  Of
>  
>
But they are probably related. The 100nF cap provides current when the 
PIC needs
it (when the system clock changes state). Without it, almost anything 
can happen.

>course, I don't know what it was.  What I do know is that it seems to have
>been cured, and I am grateful for the comments.  I tend to stay awake
>thinking about these things when they do not get solved before bedtime.  :-(
>
>Bill
>  
>


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