The first thing I always taught my techs was check the supplies. Then, when
they called from the field for help with a tough problem, I always asked if
they checked the supplies. About half the time they went had to go do it and
call back.

So: check the supplies. When doing this, check that there's a good ground
return path and that the PIC is bypassed with a suitable cap or caps (10uf
tant + .01 is good).

Then: get rid of everything but the board, the supplies and the led (w/
current limit, right?). Oh, yeah, and the crystal. Then get that working. If
the same part can't work in the demo board and your board, there's only a
few things that can be wrong, and which should be easy to find.

BTW, if you're not using the same crystal as the demo board, change that,
too. Then, when it works, change to the different crystal and get that
working. Then add the peripherals.

Good Luck. --Tom Rogers

-----Original Message-----
From: Tom Sgouros <tomfool@CIRCUS.GSO.URI.EDU>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Thursday, December 18, 1997 9:35 AM
Subject: what are the five dumbest things to check?


>Hi All:
>
>At the risk of offending the geniuses out there, I have a(nother)
>completely dumb question.  I have a PIC application that works
>beautifully on a microchip demonstration board, and won't work on my
>own.
>
>Tring to isolate the problem, I went back to a simple LED-flashing
>program (calculating delays from the main crystal).  On the demo
>board, it also works fine, but on my board it flashes irregularly,
>seeming to be "beating" with another much slower frequency.  (The
>application I am working on has a watch crystal beating a 2-second
>period on Timer1, but this appears before the interrupt is enabled.)
>
>So far as I can tell (the 30th time through), the pins are all
>connected to the right power.  MCLR is tied to 5V through a 4700ohm
>resistor.  I am using a 16C74.  The watchdog timer is disabled, and
>there are no interrupts enabled (yet).
>
>There is a 16x4 LCD attached to this all (works on the demo board, but
>doesn't initialize on mine), and I wondered if it was pulling the
>power down.  I haven't been able to detect this, but my test equipment
>is pretty rudimentary.  What would a pic do that was flirting with the
>brown-out protection?
>
>I am not expecting anyone to be able to diagnose my problems remotely,
>but I wonder if anyone who remembers their early blundering could jot
>down a list of the dumb things to check.  I need more things to try,
>since I've run out of the things I know about.  I feel like I am
>overlooking something right in front of my face, but I can't tell what
>it is.
>
>I am more or less at my wit's end (an alarmingly short distance), or I
>shouldn't have risked bothering you.  Many thanks for any help or
>advice at all,
>
>-tom
>
>p.s. Many thanks as well for the help I've already been given, both to
>questions directly asked, and for help rendered to others in similar
>trouble.  I'm learning about PICs on my own, and I don't have anybody
>here to ask these questions, and to provide reality checks.  This
>makes this list a remarkably valuable resource, despite the goats,
>dutch humor, and other distractions.
>
>----------------------------------------------------------------------
>tomss at ids.net - 401-861-2831 - 42 Forge Rd, Potowomut, RI 02818 USA
>