Telos Zephyr Xstream User Manual page 286

Let us now cover each step of the troubleshooting sequence in detail.
Step 1. Observe the behavior to find the apparent bug. In other words, determine the bug's
symptoms. Remember always that many problems are subtle and exhibit themselves via a
confusing set of symptoms.
Step 2. Observe collateral behavior to gain as much information as possible about the problem.
Does the LCD's problem correlate to an LED flashing? Try to avoid studying a problem in
isolation, but at the same time be wary of trying to fix too many at the same time. No one is
smart enough to deal with multiple problems all at once – unless they are all manifestations of
something more fundamental.
Understand that if a problem relates to telephone network routing, that your results may vary
call to call. If you suspect this may be the case, you should make repeated calls (as many as 15!)
and note the success rate. You can then change something and retest to see if the success rate
was affected by your experiment. Network related problems will frequently vary based on
which party places the call, the long distance carrier, and the bit rate; you can try varying these.
Step 3. Round up the usual suspects. At the system level, always suspect the menu set‐up, the
cables, the Phone Company line setup, the punch‐blocks, etc. At the component level, many
computer problems stem from the same sources. Never, never, never forget to check Vcc!
Step 4. Generate a hypothesis. Before changing things, formulate a hypothesis about the cause
of the problem. You probably don't have the information to do this without gathering more
data.
Sometimes you will have no clue what the problem might be. Sometimes, when the pangs of
desperation set in, it's worthwhile to try anything practically at random. You might find a bad
plug, an unconnected line, or something unexpected. Look around, but be always on the prowl
for a working hypothesis.
Step 5. Generate an experiment to test the hypothesis. Change the ISDN connection to a
known good line; call known good phone or hybrid at the other end; if long‐distance doesn't
work, try a local call.
NOTE: You should plan your tests to eliminate 50% of the possible problems in one test, if
possible. Just keep careful track so you know what you have eliminated.
Step 6. Fix the problem.
A Final Thought...
Constantly apply sanity checks. Many years ago the Firesign Theater put out an
album called "Everything You Know is Wrong". Use that as your guiding philosophy
in troubleshooting a Zephyr Xstream. For example, just because you checked the
Telco line last night, and it was fine, does not mean that it's OK now.
At 3:00 AM when the problems seem intractable and you are ready to give up
engineering, remember that the system has worked and will work. Never panic–you
are smarter than it is.
Section 13: Deep Tech Information and Troubleshooting
USER'S MANUAL
274