Have you checked the cristal? Same brand and model?

	Mark Jordan


On 10 Nov 2008 at 20:52, jmg wrote:

> Hello,
> 
> > - did you try a 2006 pic in a new board? (if you have a leftover
> pic
> > from the past)
> 
> Not yet. I have to take one from the old assembled boards.
> 
>  
> > - was there a layout change between old and new boards? (error in
> re-
> > layout or
> > new layout prone to noise)
> 
> No. No change.
> 
>  
> > - are the new pullups the value you think they are? how about
> other
> > parts in
> > that area? (new parts not in spec)
> 
> Triple checked. Everything ok.
> 
>  
> > - is the new board located differently in the final assy? (noise
> > introduced)
> 
> I used the board in the lab and in the application.
> No change in behavior.
> 
>  
> > - is power good all the time? what about brown out issues?
> 
> Yes, 5V are perfect.
> 
>  
> > - any other components change, like the brand of motherboard
> power
> > supply?
> > (maybe the signal isn't stable)
> 
> No. Anyway, the problem is not related tot he motherboard and the
> motherboard supply.
> I checked also with other brands, and with nothing connected, supply
> from 5V
> lab-PSU. I also connected the Pin 5 direct to GND of the PIC, so
> noise
> should be no issue.
> 
> 
> > - are the motherboard and pic grounds tied together and good?
> 
> See above.
> 
>  
> > and there may be others. Make a small circuit for test that also
> > samples that
> > line and is edge triggered, but could drive a buzzer, etc (another
> pic,
> > a 555,
> > etc). Put it on the line with your circuit in test and physically
> see
> > (hear)
> > when it falsely triggers. It may be only when someone touches
> > something, on a
> > regular interval, etc, which will give you more ideas on what
> the
> > source is,
> > and if the problem goes away when you add to the line, that's
> important
> > too. It
> > could even be a pic on a protoboard that also samples the line
> (or
> > drives an
> > interrupt), and could measure the time it stays high. Use a
> different
> > model pic
> > for that. If it never sees that, and the 877 does, it will get
> > interesting. ;)
> > I would also verify (compare hex files) that the code hasn't
> changed
> > since 2006
> > from a master archived copy. Also write something very simple for
> the
> > 877 that
> > doesn't do anything but sample that line and report it. Maybe use
> a
> > slightly
> > different, but simple, approach, like a loop. These tests might
> narrow
> > down a
> > software issue.
> 
> More testing is scheduled during the week.
> And I want to write a small test software ...
>  
> > All that said, this reminds me of a similar mystery 40 yrs ago or
> so
> > (TTL at
> > that point). Turns out someone had built a _small_ Van de Graf gen
> on
> > the other
> > side of [a very big] building in their space for some testing, and
> when
> > it ran,
> > a bit would mysteriously be read wrong over on my side. Of course,
> it
> > was only
> > be accident that we discovered it and solved it formally...
> 
> I know that. A long time ago, we made strange measurements in an
> EMC/EMI
> lab. Than we found out, that on the parkingplace on the supermarket
> 100
> meter ago, a gas-discharge lamp was defect, generating giant noise
> ...
> 
> But here, we tested the unit in lab and factory, and they are 500 km
> away
> from eachother ...
> 
> Best Jens 
> 
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