Hardware Reference
In-Depth Information
normal operation?
•
Establish one or more probable causes (Hypotheses and Prediction)
—What specific
components are involved or might contribute to the problem? What effect will removing or
replacing them have on the system?
•
Test the hypotheses to determine the cause (Test)
—Remove or replace suspected
components one at a time. Observe any changes in the symptoms. Repeat testing different
theories until a positive change is noted.
•
Establish a plan of action to resolve the problem and implement the solution
—Repair or
replace components that were found to be defective. Perform preventive maintenance if
applicable.
•
Verify proper functionality (Analysis)
—Test the system for proper operation. Document the
problems and solutions so as to more quickly resolve similar problems in the future.
Based on these steps, good troubleshooting follows the scientific method, which allows a clear and
concise path to solving a problem.
Troubleshooting by Replacing Parts
Using a scientific method-based approach, you can troubleshoot a PC in several ways, but in the end
it often comes down to simply reinstalling or replacing parts. That is why I normally use a simple
“known-good spare” technique that requires very little in the way of special tools or sophisticated
diagnostics.
In its simplest form, say you have two identical PCs sitting side by side. One of them has a hardware
problem; in this example let's say one of the memory modules is defective. Depending on how and
where the defect lies, this could manifest itself in symptoms ranging from a completely dead system to
one that boots up normally but crashes when running Windows or software applications. You observe
that the system on the left has the problem but the system on the right works perfectly—they are
otherwise identical. The simplest technique for finding the problem would be to swap parts from one
system to another, one at a time, retesting after each swap. At the point when the DIMMs were
swapped, upon powering up and testing (in this case testing is nothing more than allowing the system
to boot up and run some of the installed applications), the problem has now moved from one system
to the other. Knowing that the last item swapped over was the DIMM, you have just identified the
source of the problem! This did not require an expensive DIMM test machine or any diagnostics
software. Because components such as DIMMs are not economical to repair, replacing the defective
DIMM would be the final solution.
Although this is simplistic, it is often the quickest and easiest way to identify a problem component as
opposed to specifically testing each item with diagnostics. Instead of having an identical system
standing by to borrow parts from, most technicians have an inventory of what they call “known-good”
spare parts. These are parts that have been previously used, are known to be functional, and can be
used to replace a suspicious part in a problem machine. However, this is different from new
replacement parts because, when you open a box containing a new component, you really can't be
100% sure that it works. I've been in situations in which I've had a defective component and
replaced it with another (unknown to me) defective
new
component and the problem remained. Not
knowing that the new part I just installed was also defective, I wasted a lot of time checking other
parts that were not the problem.
