On Sun, 17 Jul 2016 18:48:38 -0000 (UTC), Cursitor Doom
wrote:
On Sun, 17 Jul 2016 08:34:01 -0700, Jeff Liebermann wrote:
Assumption is the mother of all screwups. If it helps, I think everyone
has the same problems with bad assumptions. It's our way of simplifying
our lives. Our brains are pre-programmed to look for patterns and
repetitions, so we generalize based on the available but usually
insufficient evidence. Don't fight it. Assumption and generalization
work well if properly used.
I wouldn't have minded so much, but a while ago we had a thread on the
golden rules of troubleshooting and my contribution was, of all things,
"assume nothing" (!)
Nice. The problem is that the common adage "assume nothing" should
really be "conclude nothing". My methods do quite a bit of assuming.
For example, I assume that recurring problems will tend to reoccur. I
assume that a manufacturer that makes crap, will continue to make
crap. I assume that companies that make marginal products will
continue to make marginal products. I assume that bad work habits
will persist for a lifetime. In repair, I assume that the gizmo in
question actually worked at one time (assuming it was not shipped dead
on arrival). Lots of assumption, most of which are not totally true
100% of the time, but are a good start.
Where we all get into trouble is when we can't distinguish between
working assumptions and a logical conclusion. Working assumption are
generalizations, which may help narrow down the cause of a problem,
but not necessarily point directly at the cause of a problem. Logical
conclusions are when we take observations, measurements, and maybe a
troubleshooting flow chart, and produce a possible culprit. The first
(assumption) helps us find the problem. The 2nd (premature
conclusion) usually distracts us in other directions.
So, you have my permission to make as many assumptions as you feel
necessary to simplify a problem, but not to draw any conclusions from
those assumptions.
I could go on forever on how I do troubleshooting. However much of it
is more intuitive than logical. That's guaranteed to produce more
confusion than enlightenment, so go with your first guess. It's usually
right.
So it's more of an art than a science? I'm not a professional technician
so I don't do these sort of things on a daily basis. Consequently my
reasoning skills are nowhere near as strong and well-developed as someone
who's fully immersed in the business.
It's neither an art or a science. It's a mixture. One cannot
troubleshoot any problem solely on the basis of science or logic. What
I think works best (for me) is an understanding of how the circuit
works or should work. From that, I can guess what I should see in
voltages and waveforms. Knowing what the circuit should NOT be doing
is as important as what it is expect to do. That will usually reduce
the problem down to the sub-section. To isolate it down to the
component is where art is best. Use of a heat gun, cold spray,
external signal source, self-heating, and just the look of a
component, are all things that are not particularly well defined, and
therefore more of an art. When both science and art fail, I try
psychology. What was the designer or manufacturer trying to
accomplish? I'm often amazed at how clear things become when I think
about the designers motivation, instead of what is facing me on the
bench.
My apologies for not being able to provide a clear and defensible
picture of how troubleshooting works. It's still much of a puzzle to
me. Sufficient to say that one starts with the science, which yields
the fundamental functions of the circuit. One then goes to the art,
where experience is more important. One then goes to psychology,
where second guessing the designer provides some possible answers.
If such philosophical issues are of interest, I suggest you get a copy
of Outliers by Malcolm Gladwell. Cheap enough used:
https://en.wikipedia.org/wiki/Outliers_(book)
http://www.alibris.com/search/books/isbn/9780316017923
"Throughout the publication, Gladwell repeatedly mentions
the "10,000-Hour Rule", claiming that the key to achieving
world class expertise in any skill, is, to a large extent,
a matter of practicing the correct way, for a total of
around 10,000 hours."
10K hrs is about 5 years of total immersion. I've found this to be
true for most everything I've tried, except my crappy piano playing.
Well over 10K hrs of practice does not compensate for a fundamental
lack of talent.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558