“Trouble-Shooting” refers to the process of locating, identifying, repairing, handling or eliminating the specified trouble AND ALSO the SOURCE or CAUSE of that trouble.

If the cause of the problem has not been found and fully handled let the customer know.

Do not pretend that the problem is handled if it is not!


1. Find out from whom you should be getting data and to whom you should be giving data. Find that person and make yourself known. The first person to see is usually the person who asked you to come fix the problem. Others may need to be contacted in order to obtain adequate information regarding the problem.

2. Find out EXACTLY what is needed and wanted. This may require speaking with various people. The owner may only be able to say that a machine is not working. On the other hand, the machine’s operator may describe an entirely different problem having nothing to do with what the owner said was the problem. The machine’s operator may be the only person who knows exactly what is or is not functioning correctly. Likewise, he too may be a source of totally false data. Beware.

3. Once you understand what is needed and wanted and how the item being addressed should work or did work then you can proceed. If you did not adequately do the preceding steps and do not know precisely what is needed and wanted, you will fail.

Sometimes, keeping the cost of the repair below some limit may be more important to the customer than repairing the trouble. This is a valid aspect of trouble-shooting that must not be ignored.

The above steps set the service man up to succeed. If the service man has thoroughly and effectively done these steps, the can proceed with the service call.


A. Determine the ideal scene for the item which is about to be serviced or repaired, just how it should work if it were working correctly, what it should and should not do or be doing, and exactly what the customer wants the product of this service call to be.

B. Determine if the reported malfunction actually exists. It may not. The report may be incorrect, or the result of a misunderstanding. The problem may also be an intermittent condition. Find out. Verify, test and observe to evaluate the problem or situation.

C. Determine when the item was last functioning correctly.

D. Determine what changed (what was done or occurred) just prior to the malfunction occurring or being noticed.

E. Go to the physical location of that change or occurrence and LOOK for whatever may have resulted from that change that may now be the cause of the trouble you have been asked to repair.

ONCE UPON A TIME, a service call to repair some lights that were out in an old church just would not resolve until the question “What changed just prior to the problem occurring?” was finally answered. Some 13 years earlier, the adjacent area had been remodeled and the lights had been out ever since. When the area of the remodel was located and closely inspected, the wires which were supposed to supply power to these lights were found under a thick blanket of dust, disconnected up in a ceiling space only a near midget could crawl through.

F. If a problem is intermittent, determine the circumstances under which the problem occurs or seems to occur.

Determine if the problem can be caused to recur and if so exactly how.

If the intermittent malfunction or failure will not recur or can not be caused to recur then it may be necessary to return at a later time when the problem can be observed. In any case do not leave without at least investigating possible or probable causes of the trouble that might be spotted just by looking.

G. Correct the source of the trouble thus found.

H. Test to verify that the trouble has been handled.

I. Test and ask to determine if other troubles exist or have been created or uncovered by the repairs just made.

J. Repeat the above until the desired product has been achieved.

K. Verify directly with the customer or his authorized representative that the desired product has indeed been achieved and that nothing further is needed or wanted. It is the customer or his authorized representative who must ultimately determine if the desired product has been achieved – not the service man.


Once you have arrived and found your way to the location of the problem, do the following:

1. Notice if it’s on fire or smoking.

2. Notice if it is turned OFF when it is thought to be ON.

3. If the problem is a power failure in a number of outlets, before doing anything further connect a loud buzzer (or at least an indicator light) that will sound (or light) should touching or wiggling something even momentarily restore power. Then proceed to wiggle and test until you find the point of failure. In minutes, problems that otherwise could have taken hours are often resolved. (The flicker of an indicator light is far easier to miss than the sound of a loud buzzer, especially from another room.)


It is important to have a thorough grasp and understanding of the difference between a PROBLEM and the SOURCE or CAUSE of a problem. To handle a PROBLEM, one MUST find and handle the SOURCE of the problem, otherwise the PROBLEM may quickly return again, and again, and again…. To be effective, a repair must terminatedly handle the problem. This requires correction of both the problem AND the cause.

For example, if the stated problem was that “the machine won’t run” and only a blown fuse was found, it is likely that the SOURCE of the PROBLEM was not found. A blown fuse is commonly an indicator of some other problem or situation. It is possible that the blown fuse itself was the total extent of the problem. The old fuse may have simply grown weary and failed, but do not assume so without checking. Often, a blown fuse is just a symptom. Find the loose fuse holder that caused the overheating, the stalled motor, or the intermittent short in the wiring, etc. and handle the cause.

At times the cause may even be laughable (an operator who sheepishly at last confesses to having temporarily jammed his machine just before the fuse blew.) Discover what caused the problem before deciding the problem has been handled.

Inform the customer as to what was found, so that he can understand. If the source of the problem has not been found, DON’T PRETEND IT HAS. Tell the customer if you believe that the source of the problem has not been found and make satisfactory arrangements to return to handle the situation when and if it recurs.


When a motor quits, fails, goes bad or burns up for ANY reason the supply line currents and voltages to the replacement motor must be measured to verify that no other errors exist. (For a single-phase motor the current in the 2 supply lines will be equal. For a three-phase motor the current in the 3 supply lines will not be equal, only close, within perhaps 10 to 20 percent of each other.) The cause of the previous motor’s failure may still exist and may still be capable of causing damage to the new motor.

Heat and moisture can cause the insulation of the motor’s windings to quickly or gradually break down and fail.

The supply voltage could be too high or too low. Either could cause a motor to fail.

The machine or mechanism being driven by the motor may be jammed or binding, thus causing the motor to draw too much current, overheat and fail. Verify by disengaging the motor from the machine or and turning the motor shaft by hand. It should turn freely. Turn the machine shaft by hand to verify that it turns freely. Measure the current on each of the supply lines to the motor while the motor is running but still disengaged from the machine.

One or more sections of the motor’s windings may have been overheated and burnt. Smell the motor and look inside with a bright light. If it smells or looks burnt and no longer runs it will be necessary to replace the motor or have it rebuilt by a motor shop.

The motor may be miswired. It can happen that no other indication of trouble may exist except that the motor appears not to have adequate power under load or that it draws more current under load than it should. By direct inspection verify that each of the motor’s internal conductors are correctly connected to each other and to the supply conductors.

A loss of voltage in any one of the 3 supply lines providing power to a 3-phase motor while the other 2 supply lines remain properly energized will cause the motor hum loudly, draw too much current, overheat, lose horsepower, not start at all, or burn up. This could result if only 1 of the 3 supply line fuses blew or if a single connection to the motor has gone bad. The solution is repair the bad connection and properly protect the motor with fuses of the correct type and size or provide some other adequate motor overload protective system. (Having only 2 of the 3 supply conductors of a 3-phase system energized is often referred to as “single phasing.”)

A single-phase motor that hums loudly, will not start, and draws too much current may not be bad. If the motor has not burnt up, replace the start capacitor and it could run like new.


It’s quite easy to get off onto a “wild goose chase.” The solution is sticking with the basics of how to trouble-shoot and calling for help when needed. Don’t just go on hoping.

Find out how whatever it is worked or should have worked before the trouble occurred. Then find out what changed or what was done or what occurred just prior to the trouble first occurring. With this data gathered and by comparing the ideal scene to the existing scene, testing and observing as needed, isolate and determine the cause of the trouble.

The procedure is the same for both complex and simple systems. This is the tech of how to trouble-shoot. Learn it and apply it and you’ll do very well as a professional trouble-shooter.

Joe Duncanson

Copyright © 1979,1980,1981,1986,2009 by Joe Duncanson. All Rights Reserved.