On Wed, Aug 04, 2010 at 11:03:33PM +0930, Roger Weichert wrote:
> If the Dataman is crook, why does the data read off all the chips ok and =
the=20
> checksum ok  ...  yet not one of the 14 I've tried have worked in it's=20
> location.

At a company I worked at many years ago (before I worked there):

A unit was returned because it would not work for the customer.  So, the=20
unit was opened up by a service technician, but it checked out to be=20
functioning properly.  It was then returned to the customer to try again. =
=20
Of course, the unit came back, and the technician tested it again - only=20
to find that it still worked fine for him.  This time, however, the=20
technician decided to test the unit after putting the cover back on (hey
there's a novel idea..).  He found that the unit would no longer work when=
=20
the cover was in place!  He then discovered that the EPROM, whose window=20
was exposed inside the sealed box, required light to hit it in order to=20
work.  So, like any good troubleshooter would do, he placed an LED inside=20
the unit, aimed at the EPROM window, to offer the light that he thought=20
the EPROM needed.  Amazed that this actually worked, the technician sent=20
the unit back to the customer.  Several months later, the unit was=20
returned again because, believe it or not(!), the unit was not reliable in=
=20
the field.  This time, a different technician looked at the EPROM circuit. =
=20
He discovered that the EPROM ground trace had never been connected in the=20
first place!  Yet many other units worked despite this PCB issue (possibly
getting ground from low address lines?)..

The impact that light had on the EPROM is still not completely understood,
but someone mentioned something about the light helping to bias the memory=
=20
cells?  I'm not sure, but I thought this story was funny from beginning to=
=20
end!

Take care,
-Chris

--=20
| Christopher Cole, Cole Design and Development, LLC          cole@coledd.c=
om |
| Embedded Software Development and Electronic Design       http://coledd.c=
om |
| Stow, Ohio, USA                                                800-518-21=
54 |
--=20
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