| By Warren Rhude To expertly troubleshoot electrical equipment, problems must be solved
by replacing only defective equipment or components in the least amount
of time. One of the most important factors in doing this, is the approach
used. An expert troubleshooter uses a system or approach that allows
them to logically and systematically analyze a circuit and determine
exactly what is wrong. The approach described here is a logical, systematic approach called
the 5 Step Troubleshooting Approach. It is a proven process that is highly
effective and reliable in helping to solve electrical problems. This approach differs from troubleshooting procedures in that it does
not tell you step by step how to troubleshoot a particular kind of circuit.
It is more of a thinking process that is used to analyze a circuit’s
behavior and determine what component or components are responsible for
the faulty operation. This approach is general in nature allowing it
to be used on any type of electrical circuit. In fact, the principles covered in this approach can be applied to many
other types of problem solving scenarios, not just electrical circuits. The 5 Step Troubleshooting Approach consists of the following:
Preparation
Step 1 Observation
Step 2 Define Problem Area
Step 3 Identify Possible Causes
Step 4 Determine Most Probable Cause
Step 5 Test and Repair
Follow-up
Let’s take a look at these in more detail.
Preparation
Before you begin to troubleshoot any piece of equipment, you must be
familiar with your organization’s safety rules and procedures for
working on electrical equipment. These rules and procedures govern the
methods you can use to troubleshoot electrical equipment (including your
lockout/tagout procedures, testing procedures etc.) and must be followed
while troubleshooting. Next, you need to gather information regarding the equipment and the
problem. Be sure you understand how the equipment is designed to operate.
It is much easier to analyze faulty operation when you know how it should
operate. Operation or equipment manuals and drawings are great sources
of information and are helpful to have available. If there are equipment
history records, you should review them to see if there are any recurring
problems. You should also have on-hand any documentation describing the
problem. (i.e., a work order, trouble report, or even your notes taken
from a discussion with a customer.) Step 1 – Observe Most faults provide obvious clues as to their cause. Through careful
observation and a little bit of reasoning, most faults can be identified
as to the actual component with very little testing. When observing malfunctioning
equipment, look for visual signs of mechanical damage such as indications
of impact, chafed wires, loose components or parts laying in the bottom
of the cabinet. Look for signs of overheating, especially on wiring,
relay coils, and printed circuit boards. Don't forget to use your other senses when inspecting equipment. The
smell of burnt insulation is something you won't miss. Listening to the
sound of the equipment operating may give you a clue to where the problem
is located. Checking the temperature of components can also help find
problems but be careful while doing this, some components may be alive
or hot enough to burn you. Pay particular attention to areas that were identified either by past
history or by the person that reported the problem. A note of caution
here! Do not let these mislead you, past problems are just that – past
problems, they are not necessarily the problem you are looking for now.
Also, do not take reported problems as fact, always check for yourself
if possible. The person reporting the problem may not have described
it properly or may have made their own incorrect assumptions. When faced with equipment which is not functioning properly you should:
- Be sure you understand how the equipment is designed to operate.
It makes it much easier to analyze faulty operation when you know
how it should operate;
- Note the condition of the equipment as found. You should
look at the state of the relays (energized or not), which lamps are
lit, which
auxiliary equipment is energized or running etc. This is the best time
to give the equipment a thorough inspection (using all your senses).
Look for signs of mechanical damage, overheating, unusual sounds, smells
etc.;
- Test the operation of the equipment including all of its
features. Make note of any feature that is not operating properly.
Make sure you
observe these operations very carefully. This can give you a lot of
valuable information regarding all parts of the equipment.
Step 2 – Define Problem Area
It is at this stage that you apply logic and reasoning to your observations
to determine the problem area of the malfunctioning equipment. Often
times when equipment malfunctions, certain parts of the equipment will
work properly while others not. The key is to use your observations (from step 1) to rule out parts
of the equipment or circuitry that are operating properly and not contributing
to the cause of the malfunction. You should continue to do this until
you are left with only the part(s) that if faulty, could cause the symptoms
that the equipment is experiencing. To help you define the problem area you should have a schematic diagram
of the circuit in addition to your noted observations. Starting with the whole circuit as the problem area, take each noted
observation and ask yourself "what does this tell me about the circuit
operation?" If an observation indicates that a section of the circuit
appears to be operating properly, you can then eliminate it from the
problem area. As you eliminate each part of the circuit from the problem
area, make sure to identify them on your schematic. This will help you
keep track of all your information.
Step 3 – Identify Possible Causes
Once the problem area(s) have been defined, it is necessary to identify
all the possible causes of the malfunction. This typically involves every
component in the problem area(s). It is necessary to list (actually write down) every fault which could
cause the problem no matter how remote the possibility of it occurring.
Use your initial observations to help you do this. During the next step
you will eliminate those which are not likely to happen.
Step 4 – Determine Most Probable Cause
Once the list of possible causes has been made, it is then necessary
to prioritize each item as to the probability of it being the cause of
the malfunction. The following are some rules of thumb when prioritizing
possible causes. Although it could be possible for two components to fail at the same
time, it is not very likely. Start by looking for one faulty component
as the culprit. The following list shows the order in which you should check components
based on the probability of them being defective:
- First look for components which burn out or have a tendency
to wear out, i.e. mechanical switches, fuses , relay contacts, or
light bulbs. (Remember, that in the case of fuses, they burn out for
a reason.
You should find out why before replacing them.)
- The next most likely cause of failure are coils, motors,
transformers and other devices with windings. These usually generate
heat and, with
time, can malfunction.
- Connections should be your third choice, especially screw
type or bolted type. Over time these can loosen and cause a high resistance.
In some cases this resistance will cause overheating and eventually
will
burn open. Connections on equipment that is subject to vibration are
especially prone to coming loose.
- Finally, you should look for is defective wiring. Pay particular
attention to areas where the wire insulation could be damaged causing
short circuits. Don't rule out incorrect wiring, especially on a new
piece of equipment.
Step 5 – Test and Repair
Testing electrical equipment can be hazardous. The electrical energy
contained in many circuits can be enough to injure or kill. Make sure
you follow all your companies safety precautions, rules and procedures
while troubleshooting. Once you have determined the most probable cause, you must either prove
it to be the problem or rule it out. This can sometimes be done by careful
inspection however, in many cases the fault will be such that you cannot
identify the problem component by observation and analysis alone. In
these circumstances, test instruments can be used to help narrow the
problem area and identify the problem component. There are many types of test instruments used for troubleshooting. Some
are specialized instruments designed to measure various behaviors of
specific equipment, while others like the multimeters are more general
in nature and can be used on most electrical equipment. A typical multimeter
can measure AC and DC Voltages, Resistance, and Current. A very important rule when taking meter readings is to predict what
the meter will read before taking the reading. Use the circuit schematic
to determine what the meter will read if the circuit is operating normally.
If the reading is anything other than your predicted value, you know
that this part of the circuit is being affected by the fault. Depending on the circuit and type of fault, the problem area as defined
by your observations, can include a large area of the circuit creating
a very large list of possible and probable causes. Under such circumstances,
you could use a “divide and eliminate” testing approach to
eliminate parts of the circuit from the problem area. The results of
each test provides information to help you reduce the size of the problem
area until the defective component is identified. Once you have determined the cause of the faulty operation of the circuit
you can proceed to replace the defective component. Be sure the circuit
is locked out and you follow all safety procedures before disconnecting
the component or any wires. After replacing the component, you must test operate all features of
the circuit to be sure you have replaced the proper component and that
there are no other faults in the circuit. It can be very embarrassing
to tell the customer that you have repaired the problem only to have
him find another problem with the equipment just after you leave. Please note, Testing is a large topic and this article has only touched
on the highlights.
Follow up
Although this is not an official step of the troubleshooting process
it nevertheless should be done once the equipment has been repaired and
put back in service. You should try to determine the reason for the malfunction.
- Did the component fail due to age?
- Did the environment the equipment operates in cause excessive corrosion?
- Are there wear points that caused the wiring to short out?
- Did it fail due to improper use?
- Is there a design flaw that causes the same component to fail repeatedly?
Through this process further failures can be minimized. Many
organizations have their own follow-up documentation and processes. Make
sure you check your organization’s procedures.
Adopting a logical and systematic approach such as the 5 Step
Troubleshooting Approach can help you to troubleshoot like an expert!
About the Author:
Warren Rhude is president of Simutech Multimedia Inc. http://www.simutechmultimedia.com,
an e-learning company that develops computer based
training simulations for electrical troubleshooting. Warren has an electrical
background and has taught troubleshooting for several years at a prominent
electrical utility.
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