Rationale of Troubleshooting


By John Frye

Knowing just what takes place during a diagnostic process is a help in becoming a better technician.

A SCREECH of brakes followed by a solid "wump" that could only mean a car crash interrupted the peaceful quiet of Mac's Service Shop. Matilda, Mac, and Barney all ran out the front door and saw two cars had collided directly in front of the shop. One of the occupants had been thrown from his car and was lying in the street with a thin trickle of blood issuing from his nostrils. As they watched, a passing motorist braked his car to a stop right in the middle of the street and hurried to the side of the injured man. He carried a small black bag, and Barney noticed the caduceus of a doctor on his license plate.

The doctor, kneeling on the pavement, took a stethoscope from his bag, and listened to the chest of the unconscious man. Next he lifted both eyelids with his thumbs and peered at the pupils. Finally he felt cautiously around the man's skull. By this time the pulsating sound of an approaching ambulance could be heard. The doctor glanced up and picked Mac's face out of the ring about him. "Mac," he said, "would you park my car for me? I think I had better go in the ambulance with this man to the hospital." Mac nodded agreement. The ambulance arrived, and the doctor supervised the careful placing of the injured man onto the stretcher and into the ambulance and took a seat beside the patient; then they were off with the siren going "wow- wow-wow-wow," but, on the doctor's orders, the ambulance was driven slowly.

Matilda and Barney were still discussing the accident when Mac came back from parking the doctor's car.

"Well," Mac offered, "if the poor devil had to get hurt, he certainly picked the right spot-and time. Doctor Wilson has the reputation of being as good a brain surgeon and diagnostician as there is in the Midwest." "He certainly seemed to know what he was doing," Barney agreed. "Every movement he made was fast but sure. I kept thinking about all the knowledge that had to be stored in his head, ready for instant recall, to enable him to know exactly what to look for." "I've thought the same thing about you and Mac when I watched you troubleshooting a TV receiver," Matilda confessed.

"I'm glad to hear you testify!" Barney exclaimed. "Lately I've been doing a lot of thinking about what really goes on in the head of a radio and TV technician when he is troubleshooting a set, and I keep being reminded that his troubleshooting and a medical diagnosis are almost identical." "Oh, oh! I smell a lecture coming on," Mac said resignedly, perching himself on a corner of Matilda's desk. "But go ahead; get it out of your system." "Okay, since you insist so eagerly," Barney replied. "Cybernetics is the key to understanding the diagnostic or troubleshooting process. Think of the brain as being a computer. The first need is to stock the basic knowledge memory bank. The doctor does this by an intense study of human anatomy in the broadest meaning of that word, covering everything from gross anatomy down to cellular respiration. What he secures from books is reinforced by what he sees with a microscope and learns in the dissecting room.

"In the same way the would-be technician must store his memory bank with a thorough and accurate knowledge of basic electrical and electronic theory. He must know how an electron behaves under the influence of chemical action, static electrical charges, and magnetic fields. He must grasp the different behaviors of direct and alternating currents.

He must know the functioning of batteries, generators, capacitors, inductances, resistances, transformers, silicon diodes, zener diodes, transistors, integrated circuits, all kinds of tubes from simple diodes to a three-gun color tube, and a host of other components too numerous to mention.

Finally, he must understand the interaction of these components when they are combined in a circuit.

"This knowledge must be both thorough and accurate, for it will color everything of a technical nature he takes into his mind from this point on. Somehow, some way, he must really understand basic theory. The form in which he acquires this knowledge will depend on the individual.

Some men find it easy to think in abstract terms about unseen electrical behavior; others need the help of analogies.

There is nothing wrong with the latter as long as it is kept in mind that no analogy is perfect and should not be forced.

For example, comparing electrical current to the flow of water helps understand many direct-current behaviors, but the analogy breaks down when you think about inductance and transformer action. The important thing is that you understand clearly, on your own terms, what takes place inside every component of an electrical circuit." "You are right about the importance of getting your basic concept of electrical theory correct," Mac chimed in. "The computer people wrap up this idea in their coined word ‘gigo.' That stands for ‘garbage in; garbage out.' In other words, if incorrect information is fed into the computer, you are going to get incorrect information out. If the technician allows fallacious and fuzzy ideas about basic electronic theory to be stored in his mind, no amount of theory is going to correct for this because he will be interpreting everything he sees in terns of his mistaken ideas about how the circuit works." "Right!" Barney agreed. "Once you've grasped what constitutes normal performance you are ready to consider abnormal performance. The doctor calls this disease, and a great deal of his education is spent learning how to recognize the difference between health as manifested in a wide range of individuals and actual disease in those individuals.

"The technician, too, must learn all the things that can go wrong with the components of his electronic circuits. Not only must he learn how these components can fail; he must also learn the tests necessary to prove that a component is incapable of proper function.

"All of this information I consider as being stored in the basic memory bank. When this bank is adequately stocked-I hasten to add `for the time being' because a good technician is going to be adding to and expanding his fund of basic knowledge all his life-it is time to start stocking the experience memory bank. Truthfully, it's difficult to draw a sharp line between what a person learns as theory and what he learns from experience because experience is actually a learning process and is bound to sharpen the knowledge of theory. For our purposes, however, we shall separate them arbitrarily. Experience is additional knowledge gained from performing the work for which the study was done.

In the doctor's case, this is acquired first as an intern; but he adds to it with every patient he treats after he hangs out his shingle.

"In the beginning the technician must apply his basic theory to problem solving because that is all he has to work with. He uses his senses to collect symptoms; he studies the circuit to see what possible component failures could produce those symptoms; and finally he evolves a theory as to what is wrong. This theory is checked by making measurements or substituting components. All diagnosis or troubleshooting is actually a matching process. You try to match the observed symptoms to a hypothetical dysfunction of the mechanism you are studying. The more accurately you observe and the more careful you are about the exact congruency of the symptoms and the hypothetical case, the more likely it is that your diagnosis will be correct.

"Unfortunately it is not always that easy. Identical symptoms can be produced by several combinations of troubles. Without experience, you have no choice but to eliminate these possibilities one by one with measurements, tests, or substitutions until you hit on the right one. After you have stocked your memory bank of experience, however, you need not follow such a haphazard procedure. Experience will have shown you some of the possibilities are much more likely to be present than others, and you will be able to check them out in the order of probability. This is a great time saver and aid to efficiency, but it does contain a trap; if experience has shown that nineteen times out of twenty a particular component failure produces a set of symptoms, you're prone to think this is always the case and change out the suspected component without verifying that it is causing the trouble. Anyone who ever changed a metal-can filter capacitor on a printed-circuit board, only to discover the hum was caused by a filament-to-heater short in a tube knows what I mean." "I know," Mac nodded his head.

"You're saying troubleshooting is a three-legged stool standing on (1)

knowledge of theory, (2) observation of symptoms, and (3) experience. Which of these legs do you consider the most important ?" "Wish you hadn't asked," Barney admitted. "I've kicked that around a lot in my own mind without corning up with a good answer. Theory is very important because of its versatility and because it makes experience much more meaningful. I think of electronic theory as being a kind of adjustable wrench that will turn many different nuts. It is just as true and applicable if you're working on a radio, a color-TV set, a tape recorder, or a garage-door opener. And when you have a good grasp of theory to interpret what you observe, your experience is far more fruitful. The Why always enriches the How.

"But anyone who has ever watched a brand-new EE trying to repair a color set also knows that theory alone is not enough-at least when time is a factor.

Experience provides the technician with a thousand shortcuts, it ranks the possibilities presented by pure theory so that 'sage experience the short process guides,' as Joel Barlow put it.

"But theory and experience are both locked in the memory banks of our computer, or brain, and can only work on information presented to it from without. That's why the observation of symptoms is so important. We're back to your ‘gigo,' for the input to the computer is what is observed by the senses directly or through the medium of instrument readings. If a technician is not keenly observant and constantly alert to the presence of obscure but pertinent symptoms, the performance of his ‘computer' is badly crippled. S-o-o-o-o, I wish you'd withdraw your question. I don't see how a good troubleshooter can possibly stand on any two of those three legs you mentioned." "Question withdrawn," Mac said.

"Really I was trying to trap you. If you had said any one was unimportant, I was ready to give you a stiff argument.

While I hesitate to say so, knowing how conceited you are, I enjoyed your little discussion. I'm always glad to see a man trying to understand how his mind works. Now let's go back into the service department and demonstrate how efficiently our troubleshooting computers work, shall we?" "If you insist," Barney grumbled.

"There are always some mundane souls who aren't happy unless they are able to make a carrier pigeon out of a golden eagle!"

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