General troubleshooting tips
When first approaching a failed or otherwise
misbehaving system, the new troubleshooter often doesn't
know where to begin. The following strategies are not
exhaustive by any means, but provide the troubleshooter with
a simple checklist of questions to ask in order to start
isolating the problem.
As tips, these troubleshooting suggestions
are not comprehensive procedures: they serve as starting
points only for the troubleshooting process. An essential
part of expedient troubleshooting is probability assessment,
and these tips help the troubleshooter determine which
possible points of failure are more or less likely than
others. Final isolation of the system failure is usually
determined through more specific techniques (outlined in the
next section -- Specific Troubleshooting Techniques).
Prior occurrence
If this device or process has been
historically known to fail in a certain particular way, and
the conditions leading to this common failure have not
changed, check for this "way" first. A corollary to this
troubleshooting tip is the directive to keep detailed
records of failure. Ideally, a computer-based failure log is
optimal, so that failures may be referenced by and
correlated to a number of factors such as time, date, and
environmental conditions.
Example: The car's engine is overheating. The last
two times this happened, the cause was low coolant level in
the radiator.
What to do: Check the coolant level
first. Of course, past history by no means guarantees the
present symptoms are caused by the same problem, but since
this is more likely, it makes sense to check this first.
If, however, the cause of routine failure in
a system has been corrected (i.e. the leak causing low
coolant level in the past has been repaired), then this may
not be a probable cause of trouble this time.
Recent alterations
If a system has been having problems
immediately after some kind of maintenance or other change,
the problems might be linked to those changes.
Example: The mechanic recently
tuned my car's engine, and now I hear a rattling noise that
I didn't hear before I took the car in for repair.
What to do: Check for something that
may have been left loose by the mechanic after his or her
tune-up work.
Function vs. non-function
If a system isn't producing the desired end
result, look for what it is doing correctly; in other
words, identify where the problem is not, and focus
your efforts elsewhere. Whatever components or subsystems
necessary for the properly working parts to function are
probably okay. The degree of fault can often tell you what
part of it is to blame.
Example: The radio works fine on
the AM band, but not on the FM band.
What to do: Eliminate from the list
of possible causes, anything in the radio necessary for the
AM band's function. Whatever the source of the problem is,
it is specific to the FM band and not to the AM band. This
eliminates the audio amplifier, speakers, fuse, power
supply, and almost all external wiring. Being able to
eliminate sections of the system as possible failures
reduces the scope of the problem and makes the rest of the
troubleshooting procedure more efficient.
Hypothesize
Based on your knowledge of how a system
works, think of various kinds of failures that would cause
this problem (or these phenomena) to occur, and check for
those failures (starting with the most likely based on
circumstances, history, or knowledge of component
weaknesses).
Example: The car's engine is
overheating.
What to do: Consider possible causes
for overheating, based on what you know of engine operation.
Either the engine is generating too much heat, or not
getting rid of the heat well enough (most likely the
latter). Brainstorm some possible causes: a loose fan belt,
clogged radiator, bad water pump, low coolant level, etc.
Investigate each one of those possibilities before
investigating alternatives. |