Latest update: 9/13/01
In trouble shooting Electronic Equipment you must have an adequate understanding of many subjects to perform the tasks well. With that said, there are many people that can do a very good job of troubleshooting without an in depth knowledge of these subjects.
Some of the subjects of most use in troubleshooting are:
While it would be great to be an expert in each of these fields, most of us will not attain that level of understanding as a hobbyist. Therefore it is probably best to use this list as a point of reference for further items we may study as time and inclination strike.
If you have looked at the list of desired skills above, you may be thinking "Gee, I don't know all of that. How can I ever troubleshoot anything?". It is easier than the list above tends to make it look. Let's start with some seemingly obvious thoughts that many people forget.
In troubleshooting, as in any other human endeavor, you must have the right attitude to succeed. You CAN solve it. It is not magic. There IS an explanation. Don't try to fix at first, just try to narrow down what may be causing the problem(s). Don't forget that this "one problem" may actually be several small, easily fixed problems that look like one major problem. Don't panic. Don't get mad. When everything seems to be going badly just ask yourself "how can I narrow it down one more time?".
Let's repeat that. Don't get mad. Look at each of the problems as a challenge to learn from rather than an impediment to progress. This single change in attitude can save you many hours of frustration and actually help speed the correction of the problem. Troubleshooting is part of the fun of Amateur Radio. Think of the satisfaction you could gain by finding and fixing a problem yourself.
Of course the fun can run out quickly if you are frustrated and have spent too much time on the same problem. If you start to feel frustrated, it's time to move to a new task. Leave the problem for a while and come back with some new ideas or call some one who can help. Rule of thumb: You shouldn't spend more than a very few hours on the same problem at one time.
Beware of one other symptom from the same source, Self-induced blindness. After a long attempt at troubleshooting a difficult problem, you can get worn out, such that crucial clues get overlooked. Take a break. You'll be amazed at what a difference this will make!
Take notes of what you find, what you see (first impressions are important) and all the "extra" symptoms you found. These will be invaluable later to help you learn what you did right and what could be done more easily. They will also guide you in your testing of the fix(es).
Notes may seem a bit trivial but there are very few people that, having not taken notes, do not find themselves duplicating effort or wondering how they got -xyz- done previously.
Another productivity aid is to draw pictures (diagrams) of the equipment as you open it up. Make note of every cable, connector, plug, jumper and gizmo you see/find. This will be an immense help at re-assembly time. If you find two cables that have the same number of wires, the same color of wires and the same connectors then use a marker and number them.
In simplest terms, make it as easy to correctly re-assemble the device as possible.
The first step of any troubleshooting involves the "investigation". List out all of the symptoms, even those that may not be involved with the problem you're looking for. The more detailed a symptom description you produce the less unnecessary work you'll end up doing - AND - a good symptom description can keep you from "fixing the wrong problem".
Before you do anything that could cause damage, insure that you take
If a system isn't producing the desired end result, look for what it is doing correctly; in other words, identify where the problem is not, and focus your efforts elsewhere. The components or subsystems necessary for the properly working parts to function are probably okay. The degree of fault can often tell you what part of it is to blame.
Effective troubleshooting requires a blend of both art and science. Unless you're lucky, your first suspicion can easily lead you away from the problem, or be dead on. Gather as much information as you can before starting work.
The investigation step can lead to obvious things like blown fuses or disconnected cables. Then, look for external causes of the failure:
Finally, a thorough inspection is invaluable.
Nonamplifying components are the most rugged of all, their relative simplicity granting them a statistical advantage over active devices. The following list gives an approximate relation of failure probabilities (top being the most likely and bottom being the least likely):
As incredible as this may sound, a high percentage of electrical and electronic system problems are caused by a very simple source of trouble: poor (i.e. open or shorted) wire connections. This is especially true when the environment is hostile, including such factors as high vibration or a corrosive atmosphere. Connection points found in any variety of plug and socket connector, terminal strip, or splice are at the greatest risk for failure. The category of "connections" also includes mechanical switch contacts, which can be thought of as a high-cycle connector. Improper wire termination lugs (such as a crimp-style connector placed on the end of a solid wire -- a definite thing to avoid unless you solder them) can cause high-resistance connections after a period of trouble-free service.
It should be noted that connections in low-voltage systems tend to be far more troublesome than connections in high-voltage systems. The main reason for this is the effect of arcing across a discontinuity (circuit break) in higher-voltage systems tends to blast away insulating layers of dirt and corrosion, and may even weld the two ends together if sustained long enough. Low-voltage systems tend not to generate such vigorous arcing across a circuit break, and also tend to be more sensitive to additional resistance in the circuit. Mechanical switch contacts used in low-voltage systems benefit from having the recommended minimum wetting current conducted through them to promote a healthy amount of arcing upon opening, even if this level of current is not necessary for the operation of other circuit components.
Although open failures tend to more common than shorted failures, "shorts" still constitute a large percentage of wiring failure modes. Many shorts are caused by degradation of wire insulation. This, again, is especially true when the environment is hostile, including such factors as high vibration, high heat, high humidity (especially salt air), or high voltage. It is rare to find a mechanical switch contact that is failed shorted, except in the case of high-current contacts where contact "welding" may occur in overcurrent conditions. Shorts may also be caused by conductive buildup across terminal strip sections or the backs of printed circuit boards.
A special case of wiring short is the ground fault, where a conductor accidently makes contact with either earth or chassis ground. This may change the voltage(s) present between other conductors in the circuit and ground, thereby causing bizarre system malfunctions and/or personnel hazard.
In this case, bad connections are usually due to assembly error, such as connection to the wrong point or poor connector fabrication. Shorted failures are also seen, but usually involve misconnections (conductors inadvertently attached to grounding points) or wires pinched under box covers.
Another wiring-related problem seen in new systems is that of electrostatic or electromagnetic interference between different circuits by way of close wiring proximity. This kind of problem is easily created by routing sets of wires too close to each other (especially routing signal cables close to power conductors), and tends to be very difficult to identify and locate with test equipment.
More often than not, you can find a bad part without ever pulling out the test equipment by using these techniques.
There are a few mistakes that many people make in electronics. Most of us tend to think that everything outside of our influence will be handled properly or the products will be manufactured correctly. Unfortunately, that is not always the case. A few things to consider are:
If the above steps don't turn anything up, the troubleshooting theory called "Half-Splitting" or what many of us know as the binary approach works quite well. It involves picking a halfway point in the bad system, and checking it there. If the signal's good at that point, move forward to the halfway point of what remains. If it's bad, go back to the halfway point between the start of the system, and where you currently are. Either way, complete your next checks and move the same way. In large systems, this can be an effective way to get to the bad area quickly.
Closely related, this is also a design and fabrication technique useful for new circuits, machines, or systems. It's always easier to begin the design and construction process in little steps, leading to larger and larger steps, rather than to build the whole thing at once and try to troubleshoot it as a whole. Countless times people will build a complex experimental circuit and have trouble getting it to work because they didn't stop, test all resistors before using them, make sure the power supply is regulating voltage properly, before trying to power anything with it and in general doing all of it in "bite sized" increments.
Active components (amplification devices) tend to fail with greater regularity than passive (non-amplifying) devices, due to greater complexity. Semiconductor devices are notoriously prone to failure due to electrical transient (voltage/current surge) overloading and thermal (heat) overloading. Electron tube devices are far more resistant to both of these failure modes, but are generally more prone to mechanical failures due to their fragile construction.
Finally, once you get the problem down to a specific circuit or component, the ability to test individual components comes into play. Unless you've got the cash or junk box to swap the part you THINK is bad, the ability to test individual parts is essential.
In a system with identical or parallel subsystems, swap components between those subsystems and see whether or not the problem moves with the swap. If it does, you've just swapped the faulty component; if it doesn't, keep searching!
This is a powerful troubleshooting method, because it gives you both a positive and a negative indication of the swapped component's fault: when the bad part is exchanged between identical systems, the broken system will start working again and the formerly good system will fail.
Sometimes, you may swap a part and find that the problem has changed, but has not gone away. This tells you that the components you just swapped are somehow different (different calibration, different function), and nothing more. However, don't dismiss this information just because it doesn't lead you straight to the problem -- look for other changes in the system as a whole as a result of the swap, and try to figure out what these changes tell you about the source of the problem.
Once you have a "culprit" then what? Simple, look a little further. Many burned out resistors, blown fuses and "fried" capacitors are the symptom rather than the cause. What caused them to expire? That will lead you closer to the actual problem.
For example, the "fried" component did so because of excessive current in the circuit. The component causing the excessive current flow may, in turn, have been affected by yet another component "upstream".
You now know (or at least think you know) what the problem is. Repair or replace the defective component(s). If you replace a suspected component and the problem changes or disappears, then that means there must have been a difference between the old and new components. Or, there might have been something fixed in the process of changing the component (such as a loose wire connection that got tightened when you changed it or a cold solder joint that was reflowed).
Be sure you maintain perspective on this. You are doing this as a hobby. Keep that in mind and most of the process will be enjoyable.
Before you "button up" the item you have been working on, start with the simplest of tests, continuity. Do you have continuity where you should and not where you shouldn't? If it fails the continuity tests then you need to determine if you are testing incorrectly or if you have further defective components.
It is FAR more cost effective (time and money) to find this type of error before applying power.
When you test, ask yourself these questions:
Much of the testing may be done while the unit is partially disassembled, but it's important to do a final test after it's "all buttoned up". This is the fun part. Use it. Try to find "another" problem while all of your new found knowledge is fresh in your mind.
If you had an intermittent, keep a few things in mind. An intermittent occurs randomly and can't be forced to occur by a specific procedure. Or, more accurately, you have not been able to isolate the sequence of events that creates the problem. You can't be certain the symptom went away unless, during symptom assessment, you record how often it happens and what - if any - other factors tend to increase its probability. This will allow you to test your fix more completely.
Manipulation, coupled with astute observation, is often the quickest way to solve an intermittent.
You found and fixed the problem. Now is time to keep YOU in shape. Troubleshooting is an intense mental effort, and must be done unemotionally. You can't keep that up for long without a break. So after each solution, take pride in your solution. Share the information you learned with your friends.
When you share information with your friends you will be amazed at the number of times they have had a similar problem. They, in turn, will likely share their experiences with you and thus you can learn many new techniques without experiencing the first-hand pain.
The last thing you need to do is a high level assessment of why the device failed. Was it because some regular maintenance was ignored? Was it from carelessness? Could the failure have been predicted? If it was none of these then just enjoy the fact that YOU found and fixed the problem. If it was from any of the problems noted above, use this information to minimize further problems.
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