troubleshooting là gì

Troubleshooting is a khuông of problem solving, often applied to tướng repair failed products or processes on a machine or a system. It is a logical, systematic tìm kiếm for the source of a problem in order to tướng solve it, and make the product or process operational again. Troubleshooting is needed to tướng identify the symptoms. Determining the most likely cause is a process of elimination—eliminating potential causes of a problem. Finally, troubleshooting requires confirmation that the solution restores the product or process to tướng its working state.

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Diagnostics[edit]

In general, troubleshooting is the identification or diagnosis of "trouble" in the management flow of 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 the causes of these symptoms.

A system can be described in terms of its expected, desired or intended behavior (usually, for artificial systems, its purpose). Events or inputs to tướng the system are expected to tướng generate specific results or outputs. (For example, selecting the "print" option from various computer applications is intended to tướng 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 tướng produce any results. (Nothing was printed, for example). Corrective action can then be taken to tướng prevent further failures of a similar kind.

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

There are two major elements required to tướng enable a troubleshooting diagnosis to tướng take place - à priori tên miền knowledge and tìm kiếm strategies.^[1] These are interdependent, and here is where we can identify fundamentally two different types of problem, with matching approaches to tướng their diagnosis. Rasmussen^[2] suggested there is strategy guided by the characteristics of the correct functioning of the device (topographic strategy), and strategy guided by the characteristics of abnormal functioning (symptomatic strategy). The second is really asking “what’s wrong?” the first is asking “what’s happening?”

A strategy is an organized mix of activities expressing a plausible way of achieving a goal. Strategies should not be viewed as algorithms, inflexibly followed to tướng solutions. Problem solvers behave opportunistically, adjusting activities within a strategy and changing strategies and tactics in response to tướng information and ideas.^[3]

A symptomatic strategy (also known as cased-based reasoning, or shallow reasoning) requires à priori tên miền knowledge that is gleaned from past experience which established connections between symptoms and causes. This knowledge is referred to tướng as shallow, compiled, evidential, history-based as well as case-based knowledge. This is the strategy most associated with diagnosis by experts. Diagnosis of a problem transpires as a rapid recognition process in which symptoms evoke appropriate situation categories.^[4] An expert knows the cause by virtue of having previously encountered similar cases. Cased based reasoning is the most powerful strategy, and that used most commonly. However, the strategy won’t work independently with truly novel problems, or where deeper understanding of whatever is taking place is sought. A topographic strategy falls into the category of deep reasoning. With deep reasoning, in-depth knowledge of a system is used. Topography in this context means a mô tả tìm kiếm or an analysis of a structured entity, showing the relations among its elements.^[5] Also known as reasoning from first principles,^[6] deep reasoning is applied to tướng novel faults when experience-based approaches aren’t viable. The topographic strategy is therefore linked to tướng à priori tên miền knowledge that is developed from a more a fundamental understanding of a system, possibly using first-principles knowledge. Such knowledge is referred to tướng as deep, causal or model-based knowledge.^[7]

Hoc^[8] noted that symptomatic approaches may need to tướng be supported by topographic approaches because symptoms can be defined in diverse terms. The converse is also true – shallow reasoning can be used abductively to tướng generate causal hypotheses, and deductively to tướng evaluate those hypotheses, in a topographical tìm kiếm.

Aspects[edit]

Usually troubleshooting is applied to tướng something that has suddenly stopped working, since its previously working state forms the expectations about its continued behavior. So the initial focus is often on recent changes to tướng the system or to tướng the environment in which it exists. (For example, a printer that "was working when it was plugged in over there"). However, there is a well known principle that correlation does not imply causality. (For example, the failure of a device shortly after it has been plugged into a different outlet doesn't necessarily mean that the events were related. The failure could have been a matter of coincidence.) Therefore, troubleshooting demands critical thinking rather than vãn magical thinking.

It is useful to tướng consider the common experiences we have with light bulbs. Light bulbs "burn out" more or less at random; eventually the repeated heating and cooling of its filament, and fluctuations in the power supplied to tướng it cause the filament to tướng crack or vaporize. The same principle applies to tướng most other electronic devices and similar principles apply to tướng mechanical devices. Some failures are part of the normal wear-and-tear of components in a system.

The first basic principle in troubleshooting is to tướng be able to tướng reproduce the problem, at wish. Second basic principle in troubleshooting is to tướng reduce the "system" to tướng its simplest khuông that still show the problem. Third basic principle in troubleshooting is to tướng "know what you are looking for. In other words, to tướng fully understand the way the system is supposed to tướng work, ví you can "spot" the error when it happens.

A troubleshooter could kiểm tra 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 regard to tướng 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 tướng "bisection" troubleshooting techniques.

It also helps to tướng start from a known good state, the best example being a computer reboot. A cognitive walkthrough is also a good thing to tướng try. Comprehensive documentation produced by proficient technical writers is very helpful, especially if it provides a theory of operation for the subject device or system.

A common cause of problems is bad design, for example bad human factors design, where a device could be inserted backward or upside down due to tướng the lack of an appropriate forcing function (behavior-shaping constraint), or a lack of error-tolerant design. This is especially bad if accompanied by habituation, where the user just doesn't notice the incorrect usage, for instance if two parts have different functions but share a common case ví that it is not apparent on a casual inspection which part is being used.

Troubleshooting can also take the khuông of a systematic checklist, troubleshooting procedure, flowchart or table that is made before a problem occurs. Developing troubleshooting procedures in advance allows sufficient thought about the steps to tướng take in troubleshooting and organizing the troubleshooting into the most efficient troubleshooting process. Troubleshooting tables can be computerized to tướng make them more efficient for users.

Some computerized troubleshooting services (such as Primefax, later renamed MaxServ), immediately show the top 10 solutions with the highest probability of fixing the underlying problem. The technician can either answer additional questions to tướng advance through the troubleshooting procedure, each step narrowing the list of solutions, or immediately implement the solution he feels will fix the problem. These services give a rebate if the technician takes an additional step after the problem is solved: report back the solution that actually fixed the problem. The computer uses these reports to tướng update its estimates of which solutions have the highest probability of fixing that particular mix of symptoms.^[9][10]

Half-splitting[edit]

Efficient methodical troubleshooting starts on with a clear understanding of the expected behavior of the system and the symptoms being observed. From there the troubleshooter forms hypotheses on potential causes, and devises (or perhaps references a standardized checklist of) tests to tướng eliminate these prospective causes. This approach is often called "divide and conquer".

Two common strategies used by troubleshooters are to tướng kiểm tra for frequently encountered or easily tested conditions first (for example, checking to tướng ensure that a printer's light is on and that its cable is firmly seated at both ends). This is often referred to tướng as "milking the front panel."^[11]

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Then, "bisect" the system (for example in a network printing system, checking to tướng see if the job reached the server to tướng determine whether a problem exists in the subsystems "towards" the user's over or "towards" the device).

This latter technique can be particularly efficient in systems with long chains of serialized dependencies or interactions among its components. It is simply the application of a binary tìm kiếm across the range of dependencies and is often referred to tướng as "half-splitting".^[12] It is similar to tướng the game of "twenty questions": Anyone can isolate one option out of a million by dividing the mix of alternatives in half đôi mươi times (because 2^10 = 1024 and 2^20 = 1,048,576).

Reproducing symptoms[edit]

One of the core principles of troubleshooting is that reproducible problems can be reliably isolated and resolved. Often considerable effort and emphasis in troubleshooting is placed on reproducibility ... on finding a procedure to tướng reliably induce the symptom to tướng occur.

Intermittent symptoms[edit]

Some of the most difficult troubleshooting issues relate to tướng symptoms which occur intermittently. In electronics this often is the result of components that are thermally sensitive (since resistance of a circuit varies with the temperature of the conductors in it). Compressed air can be used to tướng cool specific spots on a circuit board and a heat gun can be used to tướng raise the temperatures; thus troubleshooting of electronics systems frequently entails applying these tools in order to tướng reproduce a problem.

In computer programming race conditions often lead to tướng intermittent symptoms which are extremely difficult to tướng reproduce; various techniques can be used to tướng force the particular function or module to tướng be called more rapidly than vãn it would be in normal operation (analogous to tướng "heating up" a component in a hardware circuit) while other techniques can be used to tướng introduce greater delays in, or force synchronization among, other modules or interacting processes.

Intermittent issues can be thus defined:

An intermittent is a problem for which there is no known procedure to tướng consistently reproduce its symptom.

— Steven Litt, ^[13]

In particular he asserts that there is a distinction between the frequency of occurrence and a "known procedure to tướng consistently reproduce" an issue. For example, knowing that an intermittent problem occurs " within" an hour of a particular stimulus or sự kiện ... but that sometimes it happens in five minutes and other times it takes almost an hour ... does not constitute a "known procedure" even if the stimulus does increase the frequency of observable exhibitions of the symptom.

Nevertheless, sometimes troubleshooters must resort to tướng statistical methods ... and can only find procedures to tướng increase the symptom's occurrence to tướng a point at which serial substitution or some other technique is feasible. In such cases, even when the symptom seems to tướng disappear for significantly longer periods, there is a low confidence that the root cause has been found and that the problem is truly solved.

Also, tests may be lập cập to tướng stress certain components to tướng determine if those components have failed. ^[14]

Multiple problems[edit]

Isolating single component failures that cause reproducible symptoms is relatively straightforward.

However, many problems only occur as a result of multiple failures or errors. This is particularly true of fault tolerant systems, or those with built-in redundancy. Features that add redundancy, fault detection and failover to tướng a system may also be subject to tướng failure, and enough different component failures in any system will "take it down."

Even in simple systems, the troubleshooter must always consider the possibility that there is more than vãn one fault. (Replacing each component, using serial substitution, and then swapping each new component back out for the old one when the symptom is found to tướng persist, can fail to tướng resolve such cases. More importantly, the replacement of any component with a defective one can actually increase the number of problems rather than vãn eliminating them).

Note that, while we talk about "replacing components" the resolution of many problems involves adjustments or tuning rather than vãn "replacement." For example, intermittent breaks in conductors --- or "dirty or loose contacts" might simply need to tướng be cleaned and/or tightened. All discussion of "replacement" should be taken to tướng mean "replacement or adjustment or other modification."

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See also[edit]

• 5 Whys
• Bathtub curve
• Cause and effect
• Debugging
• Forensic engineering
• No Trouble Found
• Problem solving
• Root cause analysis
• RPR Problem Diagnosis

References[edit]