Basic Electrical Repair: Troubleshooting Electric Circuits 1968 US Air Force Training Film

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US Air Force Training Film TF-6078

Public domain film from the National Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and equalization (the resulting sound, though not perfect, is far less noisy than the original).

Troubleshooting is a form of problem solving, often applied to repair failed products or processes. It is a logical, systematic search for the source of a problem so that it can be solved, and so the product or process can be made operational again. Troubleshooting is needed to develop and maintain complex systems where the symptoms of a problem can have many possible causes. Troubleshooting is used in many fields such as engineering, system administration, electronics, automotive repair, and diagnostic medicine. Troubleshooting requires identification of the malfunction(s) or symptoms within a system. Then, experience is commonly used to generate possible causes of the symptoms. Determining which cause is most likely is often a process of elimination – eliminating potential causes of a problem. Finally, troubleshooting requires confirmation that the solution restores the product or process to its working state.

In general, troubleshooting is the identification of, or diagnosis of “trouble” in the management flow of a corporation or a system caused by a failure of some kind. The problem is initially described as symptoms of malfunction, and troubleshooting is the process of determining and remedying to the causes of these symptoms.

A system can be described in terms of its expected, desired or intended (usually, for artificial systems, its purpose). Events or inputs to the system are expected to generate specific results or outputs. (For example selecting the “print” option from various computer applications is intended to result in a hardcopy emerging from some specific device). Any unexpected or undesirable behavior is a symptom. Troubleshooting is the process of isolating the specific cause or causes of the symptom. Frequently the symptom is a failure of the product or process to produce any results. (Nothing was printed, for example).

The methods of forensic engineering are especially useful in tracing problems in products or processes, and a wide range of analytical techniques are available to determine the cause or causes of specific failures. Corrective action can then be taken to prevent further failures of a similar kind. Preventative action is possible using failure mode and effects analysis (FMEA) and fault tree analysis (FTA) before full scale production, and these methods can also be used for failure analysis…

A basic principle in troubleshooting is to start from the simplest and most probable possible problems first. This is illustrated by the old saying “When you see hoof prints, look for horses, not zebras”, or to use another maxim, use the KISS principle. This principle results in the common complaint about help desks or manuals, that they sometimes first ask: “Is it plugged in and does that receptacle have power?”, but this should not be taken as an affront, rather it should serve as a reminder or conditioning to always check the simple things first before calling for help.

A troubleshooter could check each component in a system one by one, substituting known good components for each potentially suspect one. However, this process of “serial substitution” can be considered degenerate when components are substituted without regards to a hypothesis concerning how their failure could result in the symptoms being diagnosed.

Simple and intermediate systems are characterized by lists or trees of dependencies among their components or subsystems. More complex systems contain cyclical dependencies or interactions (feedback loops). Such systems are less amenable to “bisection” troubleshooting techniques…

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