Do-it-yourself electronics repair. Do-it-yourself e-book repair Elimination of the most frequent breakdowns

Most often, people are interested in electronics in order to be able to repair any device. Only a small part of hobbyists engage in independent development. Although theoretical knowledge gives a general understanding of the operating principle of components, for repairs it is much more important to know the methods for checking them. We will tell you how to find a fault in an electronic circuit with your own hands, eyes and a simple tool.

Basic troubleshooting methods

Before carrying out repairs, it is important to determine what the problem is - this process is called diagnostics. So, we can distinguish two stages of checking electronic devices:

1. Checking the functionality of the device. It doesn’t always happen that the device is completely “dead”; you need to check whether the device turns on at all, or turns on and turns off immediately, or some specific buttons or functions do not work.

For example, when repairing LCD monitors, a problem such as backlight failure occurs. In this case, the monitor may either not turn on at all and its indicator blinks, or the indicator indicates the on state, but there is no image. In this case, if you shine a flashlight on the screen, you can see that there is still an image and the monitor seems to be working, but it is dark - and this is just one example when a preliminary check simplifies diagnostics.

Most problems with an electrical appliance can be identified externally. These can be either simply burnt components - diodes, resistors, transistors and capacitors, or soldering defects or mechanical damage to the elements and the printed circuit board itself.

3. Measurements. If the board and parts look normal, then you should proceed to measurements. They are carried out mainly using a multimeter and an oscilloscope. In some cases, specialized devices are used, such as frequency counters, logic analyzers, etc.

So, the generalized troubleshooting algorithm is:

Board inspection;

Determination of excessive heating of the electronic components of the board;

Measurements and dialing with a multimeter;

Using an oscilloscope and other instruments;

Replacement of a failed part or block.

Visual inspection should be carried out from general to specific. Or in simple words - inspect the general appearance of the electronic device, immediately checking the integrity of the cables and power wires. Their cover should be smooth and intact, without kinks or sharp bends, there should be no bumps or other unevenness on the shell.

After you have verified the integrity of the device, you need to disassemble it and get to the printed circuit board. Inspection of the internals should begin with checking the integrity of the cables and wires of other interconnects. It is important not to tear them during disassembly, since cables often go from the boards to the key blocks and displays mounted on the case.

After this, inspect for traces of heat or soot on the board and damaged components. Let's look at what faulty electronic components look like. For example, the housings of faulty transistors and burnt-out diodes burst or crack.

A crack or small dot appears on integrated circuits. In some cases, both burn out, leaving burning marks on the board as a result. Pay attention to whether there is a characteristic smell of burnt insulation. This way you can localize from which element or area of the board this smell comes from. You can see below how to identify burnt transistors and microcircuits.

Resistors usually burn out or darken, less often the resistive layer breaks and the part looks good.

How to identify burnt capacitors? They basically “short” between the plates and, if they are in the power circuit, then the board tracks or capacitor housing are damaged. If the circuit was low-current, a broken capacitor will simply short-circuit it without visible traces of the flow of large currents. Capacitor housings crack less often.

While electrolytic capacitors can be identified by a deformed housing cover or traces of electrolyte leaking down. There are two diagonal grooves on the cap of the capacitor; they are needed to prevent the housing from being torn apart in an emergency. In this case, the lid swells or cracks. Less often squeezes out the bottom.

With SMD components, the situation is somewhat more complicated. Often they are extremely difficult to consider for integrity. There is one method for finding a short circuit in a board with SMD - this is thermal paper, such paper is used in a cash register, so you can use any receipt. Printing on it occurs due to heating. This means that when you apply power to the board, the shorted part will overheat and be printed on the paper. You can see the troubleshooting technique using thermal paper in the video:

But you need to remember about electrical safety and not resort to this diagnostic method if you are not sure whether there is dangerous voltage there. It can be done safely and accurately.

To detect a thermal short, in most cases you will need a lab power supply or other current-limiting power source. If you are diagnosing 220V circuits, you can use a test lamp; if there is a short circuit, the lamp will light up at full intensity. In fact, it will act as a current-limiting resistor.

During a visual inspection, it is important to determine the condition of the contacts of all detachable connections. They must be clean, without oxides, with a characteristic copper or silver luster. If the contacts are not too heavily oxidized, they can be cleaned with a paper eraser or the wooden side of a match.

In more advanced cases, they need to be tinned, this way you can restore the contact surface with tin. The worst option is when there is nothing to clean or tin, then you need to either change the entire board, or solder conductors to the board tracks and connect them through them.

Also carefully inspect the traces of the printed circuit board; they can burn out, crack when the board is bent, peel off and oxidize. They are restored either with a drop of tin or a piece of wire; when the tracks are located too tightly - they are replaced with a piece of wire - a thin winding wire or twisted pair wire will do, soldering them to the beginning and end of the printed track.

To summarize, learn 5 tips for external diagnostics of electronics:

1. Most faults can be found during external inspection;

2. Carefully check the quality of soldering and the presence of microcracks;

3. Pay special attention to power circuits;

4. Swollen electrolytic capacitors in most cases are the cause of both complete inoperability and the inoperability of some individual functions;

5. A part that appears to be in good working order is not always so.

If the external examination did not bring results, then it follows. If the device does not show signs of life and:

Its fuse has blown, so we use a multimeter to test the circuit and find where we have a short circuit. The ring mode in most multimeters is combined with the diode test mode (in the figure below);

If the fuse is working, check with a voltmeter whether the supply voltage is reaching the board.

If the voltage does not come, then the problem is most likely in the cable; this can be determined by ringing the cable from the plug to the point of connection to the printed circuit board.

Do not plug the power supply directly into the network unless you are sure that you have corrected all problems. Connect in series the incandescent light bulb that we mentioned in the middle of the article.

After you have verified that the diode bridge is working properly, you should check whether voltage is present. If not, then look for a break on the board; if it does, then the method for checking it is shown in the video below:

Further diagnostics of the electronic device board consists of step-by-step measurement of the parameters of each component and comparing them with nominal values. The task is greatly simplified if you have a diagram of the device being repaired.

If you have an oscilloscope, diagnostics will be greatly simplified, since checking PWM signals at the controller output and at the bases or gates of transistors is normally only possible in this way. How to use an oscilloscope is described in the article and a number of other articles on our website from the thematic section.

Conclusion

Electronics repair is not only knowledge of the operating principle of the elements, but also intuition, experience and luck. The main thing to remember when making repairs is safety precautions - do not touch the power supply board if voltage is applied to it. Discharge the filter capacitors of the power supplies, since their terminals can carry voltages of up to 300 volts. And also when diagnosing circuits with integrated circuits, it is better to immediately look for the technical documentation for them, it can be found by searching for “datasheet name of the microcircuit”.

You can only learn what you love.
Goethe I.

"How to independently learn electronics from scratch?" - one of the most popular questions on amateur radio forums. At the same time, the answers that I found when I asked it myself did not help me much. So I decided to give mine.

This essay describes a general approach to self-study, and since it began to receive a lot of views every day, I decided to develop it and make a small guide to self-study of electronics and tell how I do it. Subscribe to the newsletter - it will be interesting!

Creativity and result

To learn something, you need to love it, be passionate about it, and practice regularly. It seems that I just voiced the truism... Nevertheless. In order to study electronics with ease and pleasure, you must love it and approach it with curiosity and admiration. Nowadays it is commonplace for everyone to be able to send a video message to the other side of the earth and instantly receive a response. And this is one of the achievements of electronics. 100 years of work of thousands of scientists and engineers.

As we are usually taught

The classical approach, which is preached in schools and universities around the world, can be called the down up. First they tell you what an electron, an atom, a charge, a current, a resistor, a capacitor, an inductance are, they force you to solve hundreds of problems to find currents in resistor circuits, then it gets even more complicated, etc. This approach is similar to climbing a mountain. But climbing up a mountain is more difficult than going down. And many give up without ever reaching the top. This is true in any business.

What if you go down the mountain? The main idea is to first get the result, and then analyze in detail why it works this way. Those. This is the classic approach of children's radio circles. It gives you the opportunity to get a feeling of victory and success, which in turn stimulates the desire to study electronics further. You see, there is very dubious benefit in studying one theory. It is imperative to practice, since not everything from theory translates 100% into practice.

There's an old engineering joke that says, "If you're good at math, you should go into electronics." Typical nonsense. Electronics is creativity, novelty of ideas, practice. And it is not necessary to fall into the jungle of theoretical calculations in order to create electronic devices. You can easily master the necessary knowledge on your own. And you will improve your mathematics in the process of creativity.

The main thing is to understand the basic principle, and only then the subtleties. This approach simply revolutionizes the world of self-paced learning. It's not new. This is how artists draw: first a sketch, then detailing. This is how various large systems are designed, etc. This approach is similar to the “poke method,” but only if you don’t look for an answer, but stupidly repeat the same action.

Did you like the device? Assemble, figure out why it is made this way and what ideas are included in its design: why exactly these parts are used, why they are connected in this way, what principles are used? Is it possible to improve anything or just replace some part?

Design is creativity, but it can be learned. To do this, you just need to perform simple actions: read, repeat other people's devices, think about the result, enjoy the process, be brave and confident.

Mathematics in Electronics

In amateur radio design, it is unlikely that you will have to calculate improper integrals, but knowledge of Ohm’s law, Kirchhoff’s rules, current/voltage divider formulas, knowledge of complex arithmetic and trigonometry can be useful. These are the basics. If you want to know more, love mathematics and physics. It is not only useful, but also extremely entertaining. Of course, this is not necessary. You can make pretty cool devices without knowing anything about it. Only these will be devices invented by someone else.

When, after a very long break, I realized that electronics was calling me again and beckoning me into the ranks of radio amateurs, it immediately became clear that my knowledge had long since disappeared, and the availability of components and technologies had become wider. What did I do? There was only one way - to admit that I was a complete zero and start from nothing: there are no experienced electronics engineers I know, there is no self-study program either, I discarded the forums because they are a dump of information and take a lot of time (you can find out some questions there in short, but it is very difficult to obtain complete knowledge - everything there is so important that you can burst!)

And then I followed the oldest and simplest path: through books. In good books, the topic is discussed most fully and there is no empty chatter. Of course, there are errors and tongue-tiedness in the books. You just need to know which books to read and in what order. After reading well-written books, the result will be excellent.

My advice is simple but useful - read books and magazines. For example, I want not only to repeat other people’s designs, but to be able to design my own. Creating is interesting and fun. This is exactly what my hobby should be: interesting and entertaining. And yours too.

What books will help you master electronics?

I spent a lot of time looking for suitable books. And I realized that I had to say thank you to the USSR. He left such an array of useful books! The USSR can be scolded, but it can be praised. It depends on what. So we must be grateful for books and magazines for radio amateurs and schoolchildren. The circulation is crazy, the authors are selected. You can still find books for beginners that will give a head start to all modern ones. Therefore, it makes sense to go to used bookstores and ask around (and you can download everything).

Klimchevsky Ch. - ABC of a radio amateur.
Aimishen. Electronics? Nothing could be simpler.
B.S. Ivanov. An oscilloscope is your assistant (how to work with an oscilloscope)
Hublowski. I. Electronics in questions and answers
Nikulin, Povny. Encyclopedia of the beginning radio amateur
Revich. Entertaining electronics
Shishkov. First steps in radio electronics
Sorcerers. Amateur radio alphabet
Bessonov V.V. Electronics for beginners and more
V. Novopolsky - Working with an oscilloscope

This is my list of books for the little ones. You should definitely flip through Radio magazines from the 70s to the 90s. After that you can already read:

Gendin. Design Tips
Kaufman, Sidman. A practical guide to circuit calculations in electronics
Volovich G. Circuitry of analog and analog-to-digital electronic devices
Tietze, Schenk. Semiconductor circuitry. 12th ed.
Shustov M. A. Practical circuitry.
Gavrilov S.A.-Semiconductor circuits. Developer secrets
Barnes. Electronic design
Milovzorov. Elements of information systems
Revich. Practical programming of AVR MK
Belov. Self-instruction manual on Microprocessor technology
Suematsu. Microcomputer control systems. First meeting
Yu.Sato. Signal Processing
D.Harris, S.Harris. Digital circuitry and computer architecture
Jansen. Digital Electronics Course

I think these books will answer many questions. More specialized knowledge can be gleaned from more specialized books: on audio amplifiers, on microcontrollers, etc.

And of course you need to practice. Without a soldering iron, the whole theory is in the hole. It's like driving a car in your head.
By the way, you can get more detailed reviews of some books from the list above.

What else should you do?

Learn to read device diagrams! Learn to analyze the circuit and try to understand how the device works. This skill only comes with practice. You need to start with the simplest schemes, gradually increasing complexity. Thanks to this, you will not only study the designations of radio elements on the diagrams, but also learn to analyze them, and also remember common techniques and solutions.

Is it expensive to do electronics?

Unfortunately, you will need money! Amateur radio is not the cheapest hobby and will require a certain minimum of finance. investments. But you can start with virtually no investment: books can be obtained from bookcrossings or borrowed from libraries, read electronically, devices can be bought to begin with, the simplest ones, and more advanced ones can be purchased when the capabilities of simple devices are not enough.

Now you can buy everything: an oscilloscope, a generator, a power supply and other measuring instruments for a home laboratory - all this should be purchased over time (or you can do it yourself what can be done at home)

But when you are small and a beginner, you can get by with a tip and parts from broken equipment that someone throws out or has simply been lying around at home for a long time without use. The main thing is to have a desire! And the rest will follow.

What to do if it doesn't work?

Continue! Rarely does anything work out well the first time. And it happens that there are no results and no results - as if you have hit an invisible barrier. Some people overcome this barrier in six months or a year, while others only after a few years.

If you encounter difficulties, then you don’t need to tear your hair out and think about yourself that you are the stupidest person in the world, since Vasya understands what reverse collector current is, but you still can’t understand why it plays a role. Maybe Vasya is just puffing out his cheeks, but he doesn’t boom-boom =)

The quality and speed of self-learning depend not only on personal abilities, but also on the environment. This is where we should rejoice at the existence of forums. There you still (and often) meet polite professionals who are ready to happily teach beginners. (There are still all sorts of grims, but I consider such people a lost branch of evolution. I feel sorry for them. Bend your fingers - this is show-off of the lowest level. It’s better to just remain silent)

Useful programs

You should definitely familiarize yourself with CAD systems: drawings of circuit diagrams and printed circuit boards, simulators, useful and convenient programs (Eagele, SprintLayout, etc.). I have dedicated a whole section on the site for them. From time to time there will be materials on working with programs that I use myself.

And most importantly, experience the joy of creativity from amateur radio! In my opinion, any business should be treated as a game. Then it will be both entertaining and educational.

About practice

Usually every radio amateur always knows what device he wants to make. But if you haven’t decided yet, then I would advise you to assemble a power source, figure out what it’s for and how each part works. Then you can turn your attention to amplifiers. And assemble, for example, an audio amplifier.

You can experiment with the simplest electrical circuits: a voltage divider, a diode rectifier, HF/MF/LF filters, a transistor and single-transistor stages, the simplest digital circuits, capacitors, inductors. All this will be useful in the future, and knowledge of such basic circuits and components will give you confidence in your abilities.

When you go step by step from the simplest to the more complex, then knowledge is layered on top of each other and it is easier to master more complex topics. But sometimes it is not clear from which bricks and how the building should be put together. Therefore, sometimes you should do the opposite: set a goal to assemble some device and master many issues when assembling it.

May Ohm, Ampere and Volt be with you:

Electronics accompany modern people everywhere: at work, at home, in the car. When working in production, no matter what specific field, you often have to repair something electronic. Let’s agree to call this “something” a “device”. This is such an abstract collective image. Today we’ll talk about all sorts of repair tricks, which, having mastered, will allow you to repair almost any electronic “device”, regardless of its design, operating principle and scope of application.

Where to begin

There is little wisdom in re-soldering a part, but finding the defective element is the main task in repair. You should start by determining the type of fault, since this determines where to start the repair.

There are three types:
1. the device does not work at all - the indicators do not light up, nothing moves, nothing buzzes, there is no response to control;
2. any part of the device does not work, that is, part of its functions is not performed, but although glimpses of life are still visible in it;
3. The device mostly works properly, but sometimes it makes so-called malfunctions. Such a device cannot yet be called broken, but still something prevents it from working normally. Repair in this case consists precisely in searching for this interference. This is considered to be the most difficult repair.
Let's look at examples of repairs for each of the three types of faults.

First category repair
Let's start with the simplest one - the first type of failure is when the device is completely dead. Anyone can guess that you need to start with nutrition. All devices living in their own world of machines necessarily consume energy in one form or another. And if our device does not move at all, then the probability of the absence of this very energy is very high. A small digression. When troubleshooting in our device, we will often talk about “probability”. Repair always begins with the process of identifying possible points of influence on the malfunction of the device and assessing the probability of each such point being involved in a given specific defect, followed by turning this probability into a fact. At the same time, to make a correct, that is, with the highest degree of probability, assessment of the influence of any block or node on the problems of the device will help the most complete knowledge of the design of the device, the algorithm of its operation, the physical laws on which the operation of the device is based, the ability to think logically and, of course , His Majesty's experience. One of the most effective methods of repair is the so-called elimination method. From the entire list of all blocks and assemblies suspected of involvement in a device defect, with varying degrees of probability, it is necessary to consistently exclude the innocent ones.

It is necessary to start the search accordingly with those blocks whose probability of being the culprits of this malfunction is the highest. Hence it follows that the more accurately this degree of probability is determined, the less time will be spent on repairs. In modern “devices” the internal nodes are highly integrated with each other, and there are a lot of connections. Therefore, the number of points of influence is often extremely large. But your experience also grows, and over time you will identify the “pest” in a maximum of two or three attempts.

For example, there is an assumption that block “X” is most likely to blame for the malfunction of the device. Then you need to carry out a series of checks, measurements, experiments that would confirm or refute this assumption. If after such experiments there remains even the slightest doubt about the non-involvement of the block in the “criminal” influence on the device, then this block cannot be completely excluded from the list of suspects. You need to look for a way to check the suspect’s alibi in order to be 100% sure of his innocence. This is very important in the elimination method. And the most reliable way to check a suspect in this way is to replace the unit with a known good one.

Let us return to our “patient”, in whom we assumed a power failure. Where to start in this case? And as in all other cases - with a complete external and internal examination of the “patient”. Never neglect this procedure, even when you are sure that you know the exact location of the breakdown. Always inspect the device completely and very carefully, without rushing. Often during an inspection you can find defects that do not directly affect the fault being sought, but which may cause a breakdown in the future. Look for burnt electrical components, swollen capacitors, and other suspicious-looking items.

If the external and internal examination does not bring any results, then pick up a multimeter and get to work. I hope there is no need to remind you about checking the presence of mains voltage and fuses. Let's talk a little about power supplies. First of all, check the high-energy elements of the power supply unit (PSU): output transistors, thyristors, diodes, power microcircuits. Then you can start sinning on the remaining semiconductors, electrolytic capacitors and, last of all, on the remaining passive electrical elements. In general, the probability of failure of an element depends on its energy saturation. The more energy an electrical element uses to operate, the greater the likelihood of its failure.

While mechanical components are worn out by friction, electrical components are worn out by current. The higher the current, the greater the heating of the element, and heating/cooling wears out any materials no worse than friction. Temperature fluctuations lead to deformation of the material of electrical elements at the micro level due to thermal expansion. Such variable temperature loads are the main reason for the so-called material fatigue effect during the operation of electrical elements. This must be taken into account when determining the order of checking elements.

Don’t forget to check the power supply for output voltage ripples or any other interference on the power buses. Although not often, such defects can cause the device to not work. Check whether the power actually reaches all consumers. Maybe due to problems in the connector/cable/wire this “food” does not reach them? The power supply will be in good working order, but there will still be no energy in the device blocks.

It also happens that the fault lies in the load itself - a short circuit (short circuit) is not uncommon there. At the same time, some “economical” power supplies do not have current protection and, accordingly, there is no such indication. Therefore, the version of the short circuit in the load should also be checked.

Now the second type of failure. Although here everything should also begin with the same external-internal examination, there is a much greater variety of aspects that should be paid attention to. - The most important thing is to have time to remember (write down) the whole picture of the state of the sound, light, digital indication of the device, error codes on the monitor, display, the position of alarms, flags, blinkers at the time of the accident. And it must be done before it is reset, acknowledged, or turned off! It is very important! Missing some important information will certainly increase the time spent on repairs. Inspect all available indications - both emergency and operational, and remember all the readings. Open the control cabinets and remember (write down) the state of the internal indication, if any. Shake the boards installed on the motherboard, cables and blocks in the device body. Maybe the problem will go away. And be sure to clean the cooling radiators.

Sometimes it makes sense to check the voltage on some suspicious indicator, especially if it is an incandescent lamp. Carefully read the readings of the monitor (display), if available. Decipher the error codes. Look at the tables of input and output signals at the time of the accident, write down their status. If the device has the function of recording the processes occurring with it, do not forget to read and analyze such an event log.

Don't be shy - smell the device. Is there a characteristic smell of burnt insulation? Pay special attention to products made of carbolite and other reactive plastics. Infrequently, but it happens that they break through, and this breakdown is sometimes very hard to see, especially if the insulator is black. Because of their reactive properties, these plastics do not warp when exposed to high temperatures, which also makes broken insulation difficult to detect.

Look for darkened insulation of relay windings, starters, electric motors. Are there any darkened resistors and other electrical radio elements that have changed their normal color and shape.

Are there any swollen or cracked capacitors?

Check if there is any water, dirt or foreign objects in the device.

See if the connector is skewed, or if the block/board is not fully inserted into its place. Try taking them out and reinserting them.

Perhaps some switch on the device is in the wrong position. The button is stuck, or the moving contacts at the switch have become in an intermediate, not fixed position. Perhaps the contact has disappeared in some toggle switch, switch, potentiometer. Touch them all (with the device de-energized), move them, turn them on. It won't be redundant.

Check the mechanical parts of the executive bodies for jamming - turn the rotors of electric motors, stepper motors. Move other mechanisms as necessary. Compare the force applied in this case with other similar working devices, if of course there is such an opportunity.

Inspect the inside of the device while it is running - you may see strong sparking in the contacts of relays, starters, switches, which will indicate an excessively high current in this circuit. And this is already a good clue for troubleshooting. Often the cause of such a breakdown is a defect in a sensor. These intermediaries between the outside world and the device they serve are usually placed far beyond the edge of the device body itself. And at the same time, they usually work in a more aggressive environment than the internal parts of the device, which are somehow protected from external influences. Therefore, all sensors require increased attention. Check their performance and take the time to clean them from dirt. Limit switches, various interlocking contacts and other sensors with galvanic contacts are high priority suspects. And in general any “dry contact” i.e. not soldered, should become an element of close attention.

And one more thing - if the device has already served for a long time, then you should pay attention to the elements that are most susceptible to any wear or change in their parameters over time. For example: mechanical components and parts; elements exposed to increased heat or other aggressive influences during operation; electrolytic capacitors, some types of which tend to lose capacity over time due to drying of the electrolyte; all contact connections; device controls.

Almost all types of "dry" contacts lose their reliability over time. Particular attention should be paid to silver-plated contacts. If the device has worked for a long time without maintenance, I recommend that before starting an in-depth troubleshooting, do preventive maintenance of the contacts - brighten them with an ordinary eraser and wipe them with alcohol. Attention! Never use abrasive pads to clean silver or gold plated contacts. This is certain death for the connector. The coating with silver or gold is always done in a very thin layer, and it is very easy to erase it with an abrasive to copper. It is useful to carry out the self-cleaning procedure for the contacts of the female part of the connector, in the professional slang of “mother”: connect and disconnect the connector several times, the springy contacts are slightly cleaned of friction. I also advise, when working with any contact connections, do not touch them with your hands - oil stains from fingers negatively affect the reliability of electrical contact. Cleanliness is the key to reliable contact operation.

The first thing is to check the operation of any blocking, protection at the beginning of the repair. (In any normal technical documentation for the device there is a chapter with a detailed description of the interlocks used in it.)

After inspecting and checking the power supply, figure out what is most likely broken in the device, and check these versions. You shouldn’t go straight into the jungle of the device. First, check all the periphery, especially the serviceability of the executive bodies - perhaps it is not the device itself that has broken down, but some mechanism controlled by it. In general, it is recommended to study, albeit not to the subtleties, the entire production process in which the device in question is a participant. When the obvious versions have been exhausted, then sit down at your desk, brew some tea, lay out diagrams and other documentation for the device and “give birth” to new ideas. Think about what else could have caused this device illness.

After some time, you should have a certain number of new versions. Here I recommend not to rush to run and check them. Sit somewhere calm and think about these versions regarding the magnitude of the probability of each of them. Train yourself in assessing such probabilities, and when you gain experience in such selection, you will begin to make repairs much faster.

The most effective and reliable way to check the functionality of a suspected unit or device assembly, as already mentioned, is to replace it with a known good one. Do not forget to carefully check the blocks for their complete identity. If you connect the unit under test to a device that is working properly, then if possible, be on the safe side - check the unit for excessive output voltages, a short circuit in the power supply and in the power section, and other possible malfunctions that can damage the working device. The reverse also happens: you connect a donor working board to a broken device, check what you wanted, and when you return it back, it turns out to be inoperative. This doesn't happen often, but keep this point in mind.

If in this way it was possible to find a faulty unit, then the so-called “signature analysis” will help to further localize the troubleshooting to a specific electrical element. This is the name of the method in which the repairman conducts an intellectual analysis of all the signals with which the tested node “lives”. Connect the block, node, board under study to the device using special extension adapters (these are usually supplied with the device) so that there is free access to all electrical elements. Lay out the circuit and measuring instruments nearby and turn on the power. Now check the signals at the control points on the board with the voltages, waveforms on the diagram (in the documentation). If the scheme and documentation do not shine with such details, strain your brains here. Good knowledge of circuit design will come in handy here.

If there are any doubts, then you can “hang” a serviceable exemplary board from a working device on the adapter and compare the signals. Check with the circuit (with documentation) all possible signals, voltages, waveforms. If a deviation of any signal from the norm is found, do not rush to conclude that this particular electrical element is faulty. It may not be the cause, but simply a consequence of another abnormal signal that forced this element to produce a false signal. During repairs, try to narrow your search and localize the fault as much as possible. When working with a suspected node/unit, come up with tests and measurements for it that would rule out (or confirm) the involvement of this node/unit in this malfunction for sure! Think seven times when you exclude a block from being unreliable. All doubts in this case must be dispelled by clear evidence.

Always do experiments intelligently; the “scientific poke” method is not our method. They say, let me poke this wire here and see what happens. Never be like such “repairers”. The consequences of any experiment must be thought out and provide useful information. Pointless experiments are a waste of time, and besides, you can break something. Develop your ability to think logically, strive to see clear cause-and-effect relationships in the operation of the device. Even the operation of a broken device has its own logic, there is an explanation for everything. If you can understand and explain the non-standard behavior of the device, you will find its defect. In the repair business, it is very important to clearly understand the operating algorithm of the device. If you have gaps in this area, read the documentation, ask everyone who knows something about the issue you are interested in. And don’t be afraid to ask, contrary to popular belief, this does not reduce your authority in the eyes of your colleagues, but on the contrary, smart people will always appreciate it positively. It is absolutely unnecessary to memorize the circuit diagram of the device; paper was invented for this purpose. But you need to know the algorithm of its operation by heart. And now you have been “shaking” the device for several days now. We have studied it so much that it seems like there is nowhere else to go. And they have repeatedly tortured all suspected blocks/nodes. Even seemingly the most fantastic options have been tried, but the fault has not been found. You are already starting to get a little nervous, maybe even panic. Congratulations! You have reached the climax of this renovation. And the only thing that can help here is... rest! You're just tired and need to take a break from work. As experienced people say, your eyes are blurry. So quit work and completely disconnect your attention from the device in your care. You can do another job, or do nothing at all. But you need to forget about the device. But when you rest, you yourself will feel the desire to continue the battle. And as often happens, after such a break you will suddenly see such a simple solution to the problem that you will be incredibly surprised!

But with a third type of malfunction, everything is much more complicated. Since malfunctions in the operation of the device are usually random, it often takes a lot of time to catch the moment the malfunction occurs. The peculiarities of the external inspection in this case consist in combining the search for a possible cause of the failure with carrying out preventive work. For reference, here is a list of some possible causes of failures.

Bad contact (first of all!). Clean the connectors all at once in the entire device and carefully inspect the contacts.

Overheating (as well as overcooling) of the entire device, caused by increased (low) ambient temperature, or caused by prolonged operation with high load.

Dust on boards, components, blocks.

Cooling radiators are dirty. Overheating of the semiconductor elements they cool can also cause failures.

Interference in the power supply. If the power filter is missing or has failed, or its filtering properties are insufficient for the given operating conditions of the device, then malfunctions in its operation will be frequent guests. Try to associate the failures with the inclusion of some load in the same electrical network from which the device is powered, and thereby find the culprit of the interference. Perhaps it is the network filter in the neighboring device that is faulty, or some other fault in it, and not in the device being repaired. If possible, power the device for a while from an uninterruptible power supply with a good built-in surge protector. The failures will disappear - look for the problem on the network.

And here, as in the previous case, the most effective method of repair is the method of replacing blocks with known good ones. When changing blocks and assemblies between identical devices, carefully ensure that they are completely identical. Pay attention to the presence of personal settings in them - various potentiometers, customized inductance circuits, switches, jumpers, jumpers, software inserts, ROMs with different firmware versions. If there are any, then make the decision to replace it after considering all the possible problems that may arise due to the risk of disruption to the operation of the unit/assembly and the device as a whole, due to differences in such settings. If there is still an urgent need for such a replacement, then reconfigure the blocks with a mandatory recording of the previous state - this will be useful when returning.

It happens that all the boards, blocks, and components that make up the device have been replaced, but the defect remains. This means that it is logical to assume that the fault is lodged in the remaining periphery in the wiring harnesses, the wiring inside some connector has come off, there may be a defect in the backplane. Sometimes the culprit is a jammed connector pin, for example in a card box. When working with microprocessor systems, running test programs several times sometimes helps. They can be looped or configured for a large number of cycles. Moreover, it is better if they are specialized test ones, and not working ones. These programs are able to record a failure and all the information accompanying it. If you know how, write such a test program yourself, focusing on a specific failure.

It happens that the frequency of a failure has a certain pattern. If the failure can be timed to the execution of a specific process in the device, then you are in luck. This is a very good lead for analysis. Therefore, always carefully monitor device failures, notice all the circumstances under which they occur, and try to associate them with the performance of some function of the device. Long-term observation of a faulty device in this case can provide a clue to solving the mystery of the failure. If you find the dependence of the occurrence of a malfunction on, for example, overheating, an increase/decrease in supply voltage, or vibration, this will give some idea of the nature of the malfunction. And then - “let the seeker find.”

The control replacement method almost always brings positive results. But the block found in this way may contain many microcircuits and other elements. This means that it is possible to restore the operation of the unit by replacing only one, inexpensive part. How to localize the search further in this case? All is not lost here either; there are several interesting techniques. It is almost impossible to catch a failure using signature analysis. Therefore, we will try to use some non-standard methods. It is necessary to provoke a block to fail under a certain local influence on it, and at the same time it is necessary that the moment of manifestation of the failure can be tied to a specific part of the block. Hang the block on the adapter/extension cord and start torturing it. If you suspect a microcrack in the board, you can try to fix the board on some rigid base and deform only small parts of its area (corners, edges) and bend them in different planes. And at the same time observe the operation of the device - catch a failure. You can try tapping the handle of a screwdriver on parts of the board. Once you have decided on the area of the board, take the lens and carefully look for the crack. Not often, but sometimes it is still possible to detect a defect, and, by the way, a microcrack is not always the culprit. Soldering defects are much more common. Therefore, it is recommended not only to bend the board itself, but also to move all its electrical elements, carefully observing their soldered connection. If there are few suspicious elements, you can simply solder everything at once so that there are no more problems with this block in the future.

But if any semiconductor element of the board is suspected as the cause of the failure, it will not be easy to find it. But here, too, you can say that there is a somewhat radical way to provoke a failure: in working condition, heat each electrical element in turn with a soldering iron and monitor the behavior of the device. The soldering iron must be applied to the metal parts of electrical elements through a thin mica plate. Heat to about 100-120 degrees, although sometimes more is required. In this case, of course, there is a certain probability of additionally damaging some “innocent” element on the board, but whether it’s worth the risk in this case is up to you to decide. You can try the opposite, cooling with ice. Also not often, but you can still try this way, as we say, “pick out a bug.” If it’s really hot, and if possible, of course, then change all the semiconductors on the board. The order of replacement is in descending order of energy and saturation. Replace several blocks at a time, periodically checking the operation of the block for failures. Try to thoroughly solder all the electrical elements on the board, sometimes just this procedure alone returns the device to a healthy life. In general, with a malfunction of this type, complete recovery of the device can never be guaranteed. It often happens that while troubleshooting you accidentally moved some element that had a weak contact. In this case, the malfunction has disappeared, but most likely this contact will manifest itself again over time. Repairing a malfunction that rarely occurs is a thankless task; it requires a lot of time and effort, and there is no guarantee that the device will be repaired. Therefore, many craftsmen often refuse to undertake the repair of such capricious devices, and, frankly, I don’t blame them for this.

In the modern world, people are surrounded by a huge number of electrical and electronic devices. Along with the undeniable advantages of such useful inventions of the human mind, we get one big minus - expensive repairs. A personal computer, a laptop, a DVD player, and a satellite receiver are complex electronic devices, the cost of repairs of which can reach several thousand rubles. Sometimes these amounts that we pay for repairs to an electronics technician are unreasonably high. But fortunately, we have the power to learn basic diagnostic techniques, as well as simple repairs that can be done at home. This article will discuss typical breakdowns of the most common electronics, as well as ways to quickly troubleshoot problems with minimal expenditure of money and nerves.

To repair electronics yourself, you don’t have to be an ace in this matter, but certain knowledge of a school physics course is still necessary. It’s good if you attended a radio engineering club at school. If you want to repair electronics, then such concepts as electrical resistance, current, emf, inductance, capacitance should not be unclear to you. Some experience in soldering radio components is required, as well as minimal skills in using an electrical tester or multimeter.

What kind of damage can you fix yourself?

Some beginners mistakenly believe that a personal computer can only be repaired in a service center. Practice shows that most breakdowns can be fixed at home using simple equipment. But it’s worth making a reservation that you most likely will not be able to replace any microcircuit on the computer’s motherboard. Although you can replace electrolytic capacitors on the same motherboard at home, armed with some simple soldering iron. Therefore, you should immediately understand which breakdowns you can fix yourself, and which ones – only in the service.

How to fix an electronic device that won't turn on

If you plug the device into a 220V power supply, but there is no reaction: there is no light or sound indication of operation, then most likely the power supply has stopped working. We recommend connecting any device that does not respond adequately when plugged into the network in series with a powerful incandescent lamp so as not to cause a short circuit. If the switching power supply of the device is working, then the incandescent lamp will not light up, but if there is a short circuit on the input of the unit, then the incandescent lamp will perform a protective function and will burn at full intensity.

How to check a switching power supply

In fact, the switching power supply has an almost standard design in many electrical devices. First, we check it for the most commonplace possible breakdowns - broken network cables and blown fuses. You can significantly speed up diagnostics if you measure the voltage across the largest capacitor in the switching power supply. As a rule, it is installed after the diode assembly and after the surge protector. If there is approximately 300V DC voltage, then you will automatically know that the fuse, the power filter, the power cable, and the input chokes are fully operational. There are blocks where instead of one huge 400V capacitor there are two. In such blocks, the voltage on each capacitor is approximately 150V. If there is no voltage, then it is best to check everything separately: ring the network cable, check each rectifier diode, fuse, capacitors, chokes, etc. Moreover, fuses can be very insidious: outwardly they look quite serviceable, but when tested they have an infinitely high resistance. This is due to the fact that in fuses, a break or burnout can occur in a place that is not at all visible.

Electrolytic capacitors are the weakest point of modern switching power supplies. A decrease in capacity and an increase in the ESR value leads either to a complete failure of the power supply unit or to a violation of the output voltage parameters. All swollen capacitors must be replaced. Also, take the time to check the ESR parameter, as well as the capacitance value of all suspicious capacitors. The compact device ESR-micro v4.0s copes best with this task. Fortunately, capacitors are not expensive, so you can simply replace any suspect capacitors with known good ones. The reliability and quality of repairs will only benefit from this. The main thing to remember is that electrolytic capacitors have polarity, therefore, they must be soldered strictly according to the loop. After replacing the capacitors, most units begin to operate normally, unless, of course, there are problems with PWM chips, diodes, output stabilization circuits, etc.

How to find a short circuit if the power supply goes into protection mode

It happens that a switching power supply starts to work normally only when disconnected from the main board. For example, the computer power supply turns on only when it is disconnected from the motherboard and “started up” using a jumper that connects the green and black wires. To find a place or radio element that provokes a short circuit, you need to spend a lot of time. To simplify this task as much as possible, we recommend applying a current-limiting constant voltage from a laboratory power supply to the problem line in the motherboard. Using touch, as well as using fax paper, we find the area where there is the highest heating. Therefore, this is where the faulty element is located. Finding and fixing the problem takes no more than 15 minutes.

How to fix a device that turns on but does not work correctly

The most difficult problem is a fault that appears and disappears. The sudden nature of the occurrence and inexplicability of the disappearance of a malfunction of electronic equipment can baffle even an experienced technician. If you notice that your computer suddenly turns off after several hours of playing, but after waiting 20-30 minutes, it is ready to work again, then you should look for a malfunction in the thermal regime, as well as in broken contacts. First of all, check which microcircuits or radio components are particularly hot. If you do not have a special temperature probe, you can simply measure the temperature by touch. Insufficient cooling, dried thermal paste, dust - these are the main causes of overheating, leading to unstable operation.

Most floor scales are made according to the same principle, so they experience the same breakdowns. To learn how to repair electronic floor scales, you will need to study several important nuances.

Device of electronic floor scales

The product consists of several elements. As a rule, experts distinguish the following parts of it:

display;
frame;
printed circuit board with various microcircuits;
strain gauges.

You need to start diagnosing a device by looking for simple problems.

The device is made of tempered glass, which rarely fails due to the high strength of the case

The process of operating a bathroom scale involves constant pressure on its surface. After this, the load will be evenly distributed across the sensors. Metal strain gauges can fail due to the passage of time. If one of them sends the wrong value, .

If the scales do not work, then repairing the scales yourself is a difficult procedure. To fix most problems, you need to use a special tool. You also need to have skills, for example, to cope with replacing and soldering a new contact.

To diagnose a breakdown, you will need to check each element of the product. If the scales are completely turned off and do not turn on, you need to disassemble them and check the integrity of all wires. If they show incorrect data, then you need to look for a problem among the strain gauges.
Elimination of the most common breakdowns
To successfully repair, you will need to follow a simple algorithm of actions. If a person wants to know how to repair an electronic floor scale, he should read the step-by-step repair instructions.
Repair of sensors
If the scales break due to sensors, first of all you will need to establish the type of problem (sensor bending, wire breakage, complete breakdown). If the malfunction is related to the curvature of the structure, it will need to be straightened. Most often, one of the load cells fails. In this case, you will need to perform the following steps.
Check the functionality of the sensors. To do this, you need to press your hands on each of them. Even with slight pressure on only 1 sensor, the scale should turn on.
Disassemble the scales and carefully examine the wiring.
If there is a break (near the board or the sensor itself), it will need to be repaired. To do this you will need to use a soldering iron.
In some cases, the break is hidden behind the adhesive base. It is necessary to carefully open it and check the reliability of the connection.

Wires connected to the strain gauge
If the sensor is completely broken, it is replaced. Finding and buying a suitable spare part on your own is quite problematic. When looking for a new load cell, you need to pay attention to its compatibility with the device. It is better to purchase it in specialized stores. When purchasing, you must use the help of consultants. The new sensor will need to be secured in the mounting location, and the wires will also need to be soldered to it.
Loop repair
Loop repair is usually required when the numbers on the display are not fully displayed. A cable is a set of wires that connects the display and the board inside the device. To assess the condition of this element and carry out repairs, perform the following steps:
Full body disassembly. Checking the integrity of the loop.
If the numbers are not fully displayed, this means that the cable is coming off.
Elements that move away from the board are securely soldered.

Fuzzy display of numbers on the display (example in the picture) may be due to its breakdown or poor-quality wire connection
You can use a special conductive glue to press the cable and all contacts to the board. After this, the problem should disappear. All gluing or soldering work must be carried out with great care. There is a possibility of damage to the board due to careless actions.
Device calibration
In some cases, the malfunction is due to incorrect sensor settings. Incorrect data may appear on the display if for some reason calibration has not been performed. Modern scales are automatically calibrated every time they are placed in a new location.

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