LA76931 Ver la hoja de datos (PDF) - Unspecified
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LA76931 Datasheet PDF : 74 Pages
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PREFACE Some Rules Of Troubleshooting
1. Safety first - know the hazards associated with the equipment you are troubleshooting. Take all safety
precautions. Expect the unexpected. Take your time.
2. Always think < what if > . This is applied both to the analytic procedures as well as to precautions with
respect to probing the equipment . When probing, insulate all but the last 1/8 inch of the probe tip to
prevent costly shorts.
3. Learn from your mistake . We all make mistakes - some of them can be quite costly. A simple problem
can turn into an expensive one due to a slip of the probe or being over eager to try something before
thinking it through. While stating that your experience in these endeavors is measured by the number
of scars you have may be stretching the point, expect to screw up - we all can point to that disaster due
to inexperience or carelessness. Just make it a point not to make the same mistake again.
4. Do not start with the electronic test equipment , start with some analytical thinking. Many problems
associated with consumer electronic equipment do not require a schematic ( though one may be useful).
The majority of problems with VCRs, CD player etc. can be dealt with using nothing more than a good
set of precision hand tools ; you built in senses and stuff between your ears represents the most
important test equipment you have.
5. If you get stuck , sleep on it . Sometimes , just letting the problem bounce around in your head, will
lead to a different more successful approach or solution. Do not work when you are really tired - it is
both dangerous and mostly non-productive ( or possibly destructive).
6. Many problems have simple solutions. Do not immediately assume that your problem is some
combination of esoteric complex convoluted failures. For a TV, it may just be a bad connection or
failed diode. Try to remember that the problems with the most catastrophic impact on operation- a
dead TV usually have the simplest solutions . The kind of problems we would like to avoid at all costs
are the ones that are intermittent or difficult to reproduce: subtle colour noise,
the occasion interference, or the dreaded horizontal output transistor blowing out every a few months
syndrome.
7. Whenever possible, try to substitute a working unit. With modular systems like component stereos and
computers, narrowing down a problem to a single unit should be the first priority. This is usually safe to
do in such case and will quickly identify which unit need work. This same principle applies at the
electronic. Note that there is the possibility of damaging the known good part by putting it into a
non-working device or vice versa. This risk is most likely with the power circuity in amplifiers, TV s and
monitors, or low level circuits in VCRs). Your frequency counter may be double triggering due to noise
or imperfect signal shape.
8. Do not blindly trust your instruments. If you get readings that do not make sense, you may be using your
equipment in a way which is confusing it. DMMs are not good at checking semiconductors in -circuit or
the power transistor you are testing may have a built in damper diode and /or base resistor. Your scope
may be picking up interference which is swamping the low level signal your are searching for. Your
frequency counter may be double triggering due to noise or imperfect signal shape.
9. Realize the coincidences do happen but are relatively rare. Usually ,there is a common cause.
For example , if a TV has no vertical deflection and no picture it is much more likely that a common power
supply output has failed than for parts in both the deflection and video subsystems to be bad.
10.Confirm the problem before diving into the repair. It is amazing how many complaints turn out to be
impossible to reproduce or are simple cockpit error. It also makes sense to identify exactly what is and
is not working so that you will know whether some fault that just appeared was actually a preexisting
problem or was caused by your poking. Try to get as much information as possible about the problem
from the owner.
11. Get used to the idea of working without a schematic. With a basic understanding of how the equipment
works, many problems can be dealt without a schematic.
12. Whenever working on precision equipment , make copious notes and diagrams. You will be eternally
grateful when the time comes to reassemble the unit.
Most connectors are keyed against incorrect insertion or interchange lengths or have slightly different
thread types. Little parts may fit in more than one place orientation. Etc.
13. Select a work area which is wide open, well lighted and where dropped parts can be located - not on a
deep pile shag rug. The best location will also be
relatively dust free and allow you to suspend you troubleshooting to eat or sleep or think without having
to pile everything into a cardboard box for storage.
14. We should get into the habit of touching a **safe** ground point first.
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