Troubleshooting in electronic circuits. Checking electronic components
Today, not a single production can do without electronics and some kind of electronic installations. Unfortunately, from time to time you have to turn to specialists for help in repairing them. But the price of electronics repairs is generally quite steep. If you have knowledge in the field of electronics, then you can try to repair broken electronics yourself, for this you need to know how to troubleshoot. There are several rules and wisdom, thanks to which you can independently repair electronics of any complexity and area of use. Of course, before you start troubleshooting, you need to check this or that.
Device diagnostics
It is not so difficult to re-solder a damaged part in an electrical appliance; it is much more difficult to correctly and accurately detect the location of the breakdown. There are three types of electronic fault detection. The order of further work depends on correct diagnosis.
- The first type includes non-working devices that do not make any sounds, indicators do not light up, and do not respond to control in any way.
- The second type includes devices in which one part is faulty. Such a device does not perform any functions, but still shows “signs of life”.
- Devices that belong to the third type cannot be called completely broken. They are in working order, but sometimes they may malfunction. It is for devices of the third type that the diagnostic stage is most important. It is believed that such electronics are more difficult to repair than completely broken ones.
Repair of devices due to breakdown of the first type
If the device does not work completely, repairing it must begin with power. Since any electronic device consumes energy, the probability of its power failure is very high. The most reliable method of detecting a malfunction can be called the elimination method.
From the list of possible problems, it is necessary to exclude incorrect options as the diagnosis progresses. First of all, you need to carefully examine the appearance of the device. This must be done even if you are sure that the cause of the malfunction is internal. After all, with such an inspection you can find defects that can damage the device in the future.
If the inspection does not bring any results, a multimeter comes to the rescue. Using this device, faults are found on the board, diodes, thyristors, input transistors and power microcircuits. If the cause of the malfunction is still not found, the electrolytic capacitors and all other semiconductors should also be checked. Passive electrical elements are checked last.
Mechanical devices are characterized by wear of friction elements, and electronics are characterized by current. The more energy an element consumes, the faster it heats up, which leads to rapid wear. The more often an element heats up and cools down, the faster the material from which it is made is deformed. Frequent temperature changes lead to the so-called fatigue effect during the use of electrical equipment.
Do not forget that the power supply must also be checked for interference generated on the power buses and differences in incoming ripple. Often the cause of inoperability is a short circuit.
Repair of devices with type 2 breakdowns
It is also necessary to begin repairing devices of the second type with an external inspection. But unlike the first type, you must try to remember the state of the light, color and digital indication of the unit, and remember the error code on the display. Next, you should continue to troubleshoot the board. The problem sometimes disappears if you clean the cooling radiators, move the cables, board, and power supplies a little. It is sometimes useful to check the voltage on an incandescent lamp.
You can also identify the problem by smell. You need to smell the device. The presence of a burning insulation smell may indicate a problem. Particular attention should be paid to elements made of reactive plastics. You need to pay attention to the switches. Their position may not match. You should also check the condition of the capacitors. Perhaps some of them are swollen or exploded. Please remember that there should be no debris, dust or water inside the device.
If the electrical appliance has been in operation for a long time, the cause of the breakdown may be wear of any mechanical elements or changes in their shape due to the friction process.
After a thorough examination appearance With the second type of device, you can begin diagnostics. You shouldn’t flattery straight into the wilds. Peripheral elements should be thoroughly examined. And only after this you can continue troubleshooting on the board.
Repair of devices with third type breakdown
Diagnostics of faults in devices of the third type is considered the most difficult, since most of the defects that arise are random. Such repairs also do not exclude the stage of inspecting the appearance of the device. Such a procedure, in this case, is also preventive in nature. Most common reasons Problems may arise:
First of all, bad contact.
Long-term loads and increased ambient temperatures can lead to overheating of the entire device.
Failures can also be caused by a layer of dust on blocks, boards and nodes.
Dirty cooling radiators contribute to overheating of semiconductor elements.
Interference with the device's power supply.
Here I plan to describe practical methods troubleshooting electronics, whenever possible, without reference to specific equipment. The reasons for inoperability include failure of the element, errors of developers, installers, etc. The methods are interrelated, and their complex application is almost always necessary. Sometimes search is very closely related to elimination. In the process of working on the text, it became clear that the methods are very interrelated and often have similar features. Perhaps we can say that the methods duplicate each other. However, it was decided not to combine similar methods into one in order to highlight problems with different sides and more fully describe the troubleshooting process.
Basic troubleshooting concepts.
1.The action must not cause harm to the device under test.
2. The action should lead to a predicted result: - putting forward a hypothesis about the serviceability or malfunction of a block, element, etc. - confirmation or refutation of the hypothesis put forward and, as a consequence, localization of the fault;
3. It is necessary to distinguish between a probable malfunction and a confirmed (detected malfunction), a put forward hypothesis and a confirmed hypothesis.
4. It is necessary to adequately assess the repairability of the product. For example, boards with elements in a BGA package have very low maintainability due to the impossibility or limited opportunity application of basic diagnostic methods.
5. It is necessary to adequately assess the profitability and need for repairs. Often, repairs are not profitable from a cost point of view, but are necessary from the point of view of developing technology, studying the product, or for some other reason.
Method description scheme:
- The essence of the method
- Method capabilities
- Advantages of the method
- Disadvantages of the method
- Application of the method
1. Finding out the history of the malfunction.
The essence of the method: The history of the occurrence of a fault can tell a lot about the location of the fault, which module is the source of system inoperability, which modules failed due to an initial fault, and the type of faulty element. Also, knowledge of the history of the occurrence of a malfunction can greatly reduce the testing time of the device, improve the quality of repairs, and the reliability of the corrected equipment. Finding out the history allows you to find out whether the malfunction is the result of external influences, such as: climatic factors (temperature, humidity, dust, etc.), mechanical influences, pollution with various substances, etc.
Method capabilities: The method allows you to very quickly put forward a hypothesis about the location of the fault.
Advantages of the method:
- There is no need to know the intricacies of the product;
- Super efficiency;
- No documentation required.
Disadvantages of the method:
- The need to obtain information about events extended over time, at which you were not present, inaccuracy and unreliability of the information provided;
- Requires confirmation and clarification by other methods; in some cases there is a high probability of error and inaccurate localization;
Application method:
- If the malfunction at first appeared rarely, and then began to appear more and more often (within a week or several years), then most likely the electrolytic capacitor is faulty, vacuum tube or a power semiconductor element, excessive heating of which leads to a deterioration in its characteristics.
- If the malfunction appears as a result of mechanical impact, then it is likely that it can be detected by external inspection of the unit.
- If a malfunction appears due to a slight mechanical impact, then its localization should begin with the use of mechanical effects on individual elements.
- If a malfunction appears after any action (modification, repair, modification, etc.) on the device, then you should pay special attention to the part of the product in which the action was performed. The correctness of these actions should be checked.
- If a malfunction appears after climatic influences, exposure to humidity, acids, vapors, electromagnetic interference, surges in supply voltage, it is necessary to check the compliance of the operational characteristics of the product as a whole and its components with the operating conditions. If necessary, take appropriate measures. (changes in working conditions or changes in the product, depending on tasks and capabilities)
- The manifestations of a fault at different stages of its development can tell a lot about the location of a fault.
2. External inspection.
The essence of the method: External inspection is often neglected, but it is external inspection that makes it possible to localize about 50% of faults, especially in small-scale production. External inspection in production and repair conditions has its own specifics.
Method capabilities:
- The method allows you to quickly identify a fault and localize it with an accuracy of the element in the presence of an external manifestation.
Advantages of the method:
- Super efficiency;
- Accurate localization;
- Minimum equipment required;
- No documentation required (or a minimum amount).
Disadvantages of the method:
- Allows you to identify only faults that are manifested in the appearance of elements and parts of the product;
- As a rule, it requires disassembling the product, its parts and blocks;
- Requires experience and excellent vision.
Application method:
- In production conditions, special attention must be paid to the quality of installation. The quality of installation includes: correct placement of elements on the board, quality of solder connections, integrity of printed conductors, absence of foreign inclusions in the board material, absence of short circuits (sometimes short circuits are visible only under a microscope or at a certain angle), integrity of insulation on wires, reliable fastening of contacts in the connectors. Sometimes an unsuccessful design provokes short circuits or breaks.
- In a repair situation, you should find out if the device has ever worked correctly. If it did not work (a case of a factory defect), then you should check the quality of installation.
- If the device worked normally, but failed (a case of actual repair), then you should pay attention to traces of thermal damage to electronic elements, printed conductors, wires, connectors, etc. Also, during inspection, it is necessary to check the integrity of the insulation on the wires, cracks from time, cracks as a result of mechanical stress, especially in places where conductors are subject to bending (for example, sliders and flips of mobile phones). Particular attention should be paid to the presence of dirt, dust, leakage of electrolyte and odor (burnt, mold, feces, etc.). The presence of contamination may be the cause of the inoperability of the electronic equipment or an indicator of the cause of the malfunction (for example, leakage of electrolyte).
- Inspecting a printed circuit board requires good lighting. It is advisable to use a magnifying glass. As a rule, shorts between solders and poor-quality solders are visible only from a certain viewing angle and lighting.
Naturally, in all cases you should pay attention to any mechanical damage to the housing, electronic elements, boards, conductors, screens, etc.
3. Dialing.
The essence of the method: The essence of the method is that, using an ohmmeter, in one form or another, the presence of the necessary connections and the absence of unnecessary connections (short circuits) are checked.
Method capabilities:
- Prevention of faults during production, quality control of installation;
- Testing the hypothesis about the presence of a fault in a specific circuit;
Advantages of the method:
- simplicity;
- high qualification of the performer is not required;
- high reliability;
- precise fault localization;
Disadvantages of the method:
- high labor intensity;
- restrictions when checking boards with mounted elements and connected harnesses, elements within the circuit.
- the need to gain direct access to contacts and elements.
Application method:
- In practice, as a rule, it is enough to check the presence of the necessary connections. The absence of short circuits is checked only through the power supply circuits.
- Absence unnecessary connections is also provided by technological methods: marking and numbering of wires in the harness.
- A check for the presence of unnecessary connections is carried out when there is a suspicion of specific conductors, or a suspicion of a design error.
- Checking for redundant connections is extremely labor-intensive. In this regard, it is carried out as one of the final stages, when a possible area of closure (for example, there is no signal at the control point) is localized by other methods.
- You can very accurately localize a short circuit using a milliohmmeter, with an accuracy of several centimeters.
- Although this technique has certain disadvantages, it is very widely used in small-scale production due to its simplicity and efficiency.
- It is better to dial according to the dialing table compiled on the basis of the electrical circuit diagram. In this case, they are corrected possible errors design documentation and ensures that there are no errors in the dialing itself.
4. Performance measurements
The essence of the method. When using this method, the product is turned on under operating conditions or under conditions simulating operating conditions. And they check the characteristics, comparing them with the necessary characteristics of a working product or theoretically calculated ones. It is also possible to measure the characteristics of a separate block, module, or element in a product.
Method capabilities:
- Allows you to quickly diagnose the product as a whole or a separate unit;
- Allows approximately evaluate location of the fault, identify the functional unit that is not working correctly if the product is not working correctly;
Advantages of the method:
- Quite high efficiency;
- Accuracy, adequacy;
- Evaluation of the product as a whole;
Disadvantages of the method:
- Necessity specialized equipment or, at a minimum, the need to assemble a connection diagram;
- The need for standard equipment;
- The need for a sufficiently high qualification of the performer;
- It is necessary to know the principles of operation of the device, the composition of the device, its block diagram (to localize the fault).
Application method: For example:
- The TV is checked for the presence of an image and its parameters, the presence of sound and its parameters, power consumption, and heat dissipation. Based on the deviation of certain parameters, the serviceability of the functional blocks is judged.
- IN mobile phone The tester checks the parameters of the RF path and, based on the deviation of certain parameters, judges the serviceability of the functional blocks.
- Naturally, you need to be sure that all external units are in working order and that input signals. To do this, the operation of the product (element, block) is compared with the operation of a serviceable one under the same conditions and in this connection circuit. This does not mean theoretically the same circuit, but practically the same hardware. Or you need to compare all input signals.
5. Observation of the passage of signals through cascades.
The essence of the method: Using measuring equipment (oscilloscope, tester, spectrum analyzer, etc.), the correct propagation of signals through the cascades and circuits of the device is observed. To do this, measurements of signal characteristics are carried out in control points.
Method capabilities:
- assessment of the performance of the product as a whole;
- performance assessment of cascades and functional blocks;
Advantages of the method:
- high accuracy of fault localization;
- adequacy of assessment of the condition of the product as a whole and in cascades;
Disadvantages of the method:
- great difficulty in assessing feedback circuits;
- the need for highly qualified performers;
- labor intensity;
- ambiguity of results if used incorrectly;
Application method:
- In circuits with a sequential arrangement of cascades, the loss of the correct signal at one of the control points indicates a possible malfunction of either the output, or a short circuit to the input, or a communication fault.
- First, they isolate the built-in signal sources (clock generators, sensors, power modules, etc.) and sequentially find a node in which the signal does not correspond to the correct one described in the documentation or determined using simulation.
- After checking the correct functioning of the built-in signal sources, test signals are supplied to the input (or inputs) and the correctness of their propagation and conversion is again monitored. In some cases, for more effective application of the method, a temporary modification of the circuit is required, i.e. if necessary and possible - break the feedback circuits, break the input and output communication circuits of the suspected cascades
Fig. 1 Temporary modification of the device to eliminate ambiguity in the location of the fault. Crosses indicate a temporary break in connections.
- In circuits with feedback it is very difficult to obtain unambiguous results.
6. Comparison with a working unit.
The essence of the method: The point is that they compare various characteristics a known good product and a faulty one. According to the differences in appearance, electrical signals, electrical resistance judge the location of the fault. Method capabilities:
- Operative diagnostics in combination with other methods;
- Possibility of repair without documentation.
Advantages of the method:
- Operational troubleshooting;
- There is no need to use documentation;
- Eliminates modeling and documentation errors;
Disadvantages of the method:
- The need to have a working product;
- Need for combination with other methods
Application method: Comparison with a working unit is a very effective method, because not all characteristics of the product and signals in all circuit nodes are documented. It is necessary to start the comparison by comparing the appearance, arrangement of elements and configuration of conductors on the board; differences in installation indicate that the design of the product has been changed and, quite possibly, an error was made. The various electrical characteristics are then compared. To compare the electrical characteristics, look at the signals at various points in the circuit, the operation of the device in different conditions, depending on the nature of the malfunction. It is quite effective to measure electrical resistance between different points (peripheral scanning method).
7.Modeling.
The essence of the method: The behavior of a serviceable and faulty device and based on the simulation, a hypothesis about a possible malfunction is put forward, and then the hypothesis is verified by measurements. The method is used in combination with other methods to increase their effectiveness.
Method capabilities:
- Prompt and adequate generation of a hypothesis about the location of the fault;
- Preliminary testing of the hypothesis about the location of the fault.
Advantages of the method:
- Ability to work with intermittent faults,
- Adequacy of assessment.
Disadvantages of the method:
- highly qualified performer is required,
- combination with other methods required
Application method: When eliminating an intermittent malfunction, it is necessary to use modeling to determine whether the element being replaced could provoke this malfunction. To model, it is necessary to understand the operating principles of the equipment and sometimes even know the subtleties of its operation.
8.Partition into functional blocks.
The essence of the method: To pre-locate a fault, it is very effective to divide the device into functional blocks. It should be taken into account that often the design division into blocks is not effective from a diagnostic point of view, since one structural block can contain several functional blocks or one functional block can be structurally made in the form of several modules. On the other hand, the structural block is much easier to replace, which makes it possible to determine which structural block contains the fault.
Method capabilities:
- Allows you to optimize the use of other methods;
- Allows you to quickly determine the area where the fault is located;
- Allows you to work with complex faults
Advantages of the method:
- Speeds up the troubleshooting process;
Disadvantages of the method:
- A thorough knowledge of the product's circuitry is required;
- It takes time to thoroughly analyze the device
Application method: There are two options:
- If the product consists of blocks (modules, boards) and their quick replacement is possible, then, changing the blocks one by one, they find the one whose replacement the fault disappears;
- In another option, by analyzing the documentation, they draw up a functional diagram of the device, based on the functional diagram, model (usually mentally) the operation of the product and put forward a hypothesis about the location of the fault.
9. Temporary modification of the circuit.
The essence of the method: To eliminate mutual influence and to eliminate ambiguity in measurements, sometimes it is necessary to change the product circuit: break connections, connect additional connections, solder or solder elements.
Method capabilities:
- Localization of faults in circuits with OS;
- Accurate fault localization;
- Elimination of mutual influence of elements and circuits.
Advantages of the method:
- Allows you to clarify the location of the fault.
Disadvantages of the method:
- The need to modify the system
- The need to know the intricacies of the device's operation
Application method: Partial disconnection of circuits is used in the following cases:
- when the circuits influence each other and it is unclear which of them is the cause of the malfunction;
- when a faulty unit can damage other units;
- when there is an assumption that an incorrect/faulty circuit is blocking the operation of the system.
Particular care should be taken when disconnecting protection circuits and negative feedback circuits, because Disabling them may result in significant damage to the product. Disabling the feedback circuits can lead to a complete disruption of the operation mode of the cascades and, as a result, not give the desired result. Opening the PIC circuit in generators naturally leads to generation failure, but can allow the characteristics of the cascades to be removed.
10. Switching on a functional block outside the system, in conditions simulating the system.
The essence of the method: In essence, the method is a combination of methods: Division into functional blocks and Removal of external operating characteristics. When faults are detected, the “suspected” block is checked outside the system, which allows either to narrow the search if the block is working, or to localize the fault within the block if the block is faulty.
Method capabilities:
- testing a hypothesis about the performance of a particular part of the system
Advantages of the method:
- the ability to test and repair a functional unit without a system.
Disadvantages of the method:
- the need to assemble a verification scheme.
Application method: When applying this method, it is necessary to monitor the correctness of the conditions created and the tests used. Blocks may be poorly coordinated with each other at the development stage.
11.Preliminary check of functional blocks.
The essence of the method: The functional block is pre-tested outside the system, on a specially made stand (workstation). During repairs this method makes sense if the block does not require too many input signals or, in other words, it is not too difficult to simulate the system. For example, this method makes sense to use when repairing power supplies. Method capabilities:
- Testing the hypothesis about the unit’s performance;
- Prevention of possible malfunctions when assembling large systems.
Advantages of the method:
- Possibility of checking the main characteristics of the unit without interfering influences;
- Possibility of pre-checking blocks.
Disadvantages of the method:
- The need to collect a verification scheme
Application method: It is very widely used to prevent system malfunctions in the production of new products.
12. Replacement method.
The essence of the method: The suspected unit/component is replaced with a known good one, and the functioning of the system is checked. Based on the test results, the correctness of the hypothesis regarding the malfunction is judged.
Method capabilities:
- Testing the hypothesis about the serviceability or failure of a block or element.
Advantages of the method:
- Efficiency.
Disadvantages of the method:
- The need for a replacement block.
Application method: Several cases are possible: when the behavior of the system has not changed, this means that the hypothesis is incorrect; when all the faults in the system are eliminated, that means. the fault is really localized in the replaced unit; when some of the defects have disappeared, this may mean that only the secondary fault has been eliminated and the serviceable unit will burn out again under the influence of the primary system defect. In this case, perhaps the best solution will re-install the replaced unit (if possible and appropriate) and continue troubleshooting with that. to eliminate the root cause. For example, a faulty power supply can lead to unsatisfactory operation of several units, one of which will fail as a result of overvoltage.
13. Checking the operating mode of the element.
The essence of the method: The values of currents and voltages in the circuit are compared with the presumably correct ones. They can be found in the documentation, calculated during modeling, measured when examining a working unit. Based on this, a conclusion is made about the serviceability of the element.
Method capabilities:
- Fault localization accurate to the element.
Advantages of the method:
- Accuracy
Disadvantages of the method:
- Slowness
- Highly qualified performer is required;
Application method:
- Check the correctness of logic levels digital circuits(compliance with standards, and also compared with normal, typical levels);
- check the voltage drops on diodes and resistors (compare with the calculated value or with the values in a working unit);
- Measure voltages and currents at control points.
14. Provoking effects.
The essence of the method: Increase or decrease in temperature, humidity, mechanical impact. The use of such influences is very effective for detecting intermittent faults.
Method capabilities:
- Detection of intermittent faults.
Advantages of the method:
- A straw for a drowning man. :-)
- In some cases, it is enough to use your hands or a screwdriver.
Disadvantages of the method:
- Often special equipment is required.
Application method: As a general rule, you should start by tapping the elements. Try to touch the elements and harnesses. Heat the board under a lamp. In more difficult cases special cooling methods or climatic chambers are used.
15. Checking the element temperature.
The essence of the method is simple, with any measuring device (or finger) you need to estimate the temperature of the element, or draw a conclusion about the temperature of the element based on indirect signs (tarnished colors, burnt smell, etc.). Based on these data, a conclusion is made about a possible malfunction of the element.
Application method: In general, everything is simple and clear; the difficulty arises when assessing high-voltage circuits. And it is not always clear whether the element is in normal mode or is overheating. In this case, you need to compare it with a working product.
16. Execution of test programs.
The essence of the method: A running system runs a test program that interacts with various system components and provides information about their response, or the system, under the control of a test program, controls peripheral devices and the operator observes the response peripheral devices, or a test program allows you to observe the response of peripheral devices to a test effect (key press, reaction of a temperature sensor to a temperature change, etc.).
Advantages of the method: The advantages of the method include a very quick assessment based on the criterion of whether it works or not.
Disadvantages of the method: The method has significant disadvantages, because To execute the test program, the system core must be in good condition; an incorrect response does not allow the fault to be accurately localized (both the periphery, the system core, and the test program may be faulty).
Application method: The method is only applicable for final testing and eliminating very minor defects.
17. Step-by-step execution of commands.
The essence of the method: Using special equipment, the microprocessor system is transferred to the mode of step-by-step (step-by-step) execution of instructions (machine codes). At each step, the state of the buses (data, addresses, control, etc.) is checked and, by comparison with the model or with a working system, conclusions are drawn about the operation of the device components. This method can be classified as one of the varieties of the “test program execution method”, but the method can be used on an almost inoperable system.
Advantages of the method:
- It is possible to debug an almost idle system;
- Low cost of necessary equipment.
Disadvantages of the method:
- Very labor intensive.
Application method: The method is very effective for debugging microprocessor systems at the development stage.
18. Test signatures.
The essence of the method: Using special equipment, the state of the microprocessor device buses is determined in normal operating mode at each step of the program (or test program). We can say that this is a version of step-by-step execution of programs, only faster (due to the use of special equipment).
Advantages of the method:
- It is possible to debug an almost idle system
Disadvantages of the method:
- Great labor intensity.
- Highly qualified performer.
Application method: The method is very effective for debugging microprocessor systems at the development stage.
19. "Exit to entrance."
The essence of the method: If a product/system has an output (multiple outputs) and has an input (multiple inputs) and the input/output can operate in duplex mode, then it is possible system check, in in which the signal from the output is fed to the input through external connections. The presence/absence of a signal, its quality are analyzed and based on the results an assessment is made of the performance of the corresponding circuits.
Advantages of the method:
- Very high speed performance assessments
- Minimum additional equipment
- Disadvantages of the method:
- Limited application
Application method:
- Used for final testing of control systems. Maybe somewhere else.
20. Typical faults.
The essence of the method: Based on past repair experience for a specific product, a list of fault manifestations and the corresponding faulty item is compiled. The method is based on the fact that mass-produced products have weak points and defects, which, as a rule, lead to product failure. This method also includes the assumption that one or another element will fail based on reliability indicators.
Advantages of the method:
- High speed
- Not very highly qualified performer
Disadvantages of the method:
- Not applicable in the absence of fault statistics;
- Requires confirmation of the hypothesis by other methods.
Application method: Most specialists keep statistics and symptoms of malfunctions in their heads. I have seen attempts at systematic presentation in the “Service Manuals” (repair documentation) of the Nokia company.
21. Analysis of the impact of a malfunction.
The essence of the method: Based on the available information about the manifestation of the malfunction and the premise that all manifestations are caused by one malfunction, the device is analyzed. In this analysis, a “tree” of mutual influences of blocks (elements) is built and a block (element) is found, the malfunction of which could cause all (most) manifestations. If there is no solution, additional information is collected.
Advantages and disadvantages: As information is collected and obtained, it must be constantly analyzed from the point of view of this method. The method is as necessary as air. Without him - nowhere.
Application method: For example, the simplest case is that the device does not turn on at all. No heating extraneous sounds, no burning smell. When putting forward a hypothesis, it is necessary to assume a minimal cause and minimal harm - this is a blown fuse. Checking the fuse. If the fuse is working, we continue to collect information. The key principle is the assumption that minimal cause.
22. Peripheral scanning.
The essence of the method: Measure the resistance between the test points. It differs from dialing in that we are interested in the value of resistance, and not just the presence or absence of a connection. The term “Checkpoint” is used in a broad sense. The control points can be chosen by the performer himself.
Advantages of the method:
- Possibility of automated control based on the “pass/fail” criterion
- Possibility of in-circuit checking of elements
- A sample or database of resistances in a working unit is required
- It is difficult to make a theoretical assumption about the correct value of resistance, especially if the circuit is complex and branched.
Application method: To measure resistance, it is necessary to use equipment that prevents failure of the device as a result of measurements. You can use both the tester in repair conditions and the machines as part of a large production line.
So you go to the kettle to celebrate with the thought of slamming a mug of tea with a steering wheel in honor of the device you just assembled, but it suddenly stopped working. In this case, there are no visible reasons: the capacitors are intact, the transistors do not seem to smoke, and the diodes too. But the device does not work. What should I do? You can use this simple troubleshooting algorithm:
Installation "snot"
“Snot” is a small drop of solder that creates a short circuit between two different traces on a printed circuit board. During home assembly, such unpleasant drops of solder lead to the fact that the device either simply does not start, or does not work correctly, or, worst of all, expensive parts immediately burn out after switching on.
To avoid such unpleasant consequences, before turning on the assembled device, you should carefully check printed circuit board for the presence of short circuits between tracks.
Device diagnostic devices
The minimum set of instruments for setting up and repairing amateur radio structures consists of, a multimeter and. In some cases, you can only get by with a multimeter. But for more convenient debugging of devices, it is still advisable to have an oscilloscope.
For simple devices This set is enough for the eyes. As for, for example, debugging various amplifiers, then for them correct settings It is advisable to also have a signal generator.
Proper nutrition is the key to success
Before drawing any conclusions about the performance of the parts included in your amateur radio design, you should check whether the correct power is supplied. Sometimes it turns out that the problem was due to poor nutrition. If you start checking the device with its power supply, you can save a lot of time on debugging if the problem was in it.
Diode check
If there are diodes in the circuit, then they should be carefully checked one by one. If they are apparently intact, then you should unsolder one terminal of the diode and check it with a multimeter turned on in resistance measurement mode. Moreover, if the polarity of the multimeter terminals coincides with the polarity of the diode terminals (+ terminal to the anode, and - terminal to the cathode), then the multimeter will show approximately 500-600 Ohms, and in reverse connection (- terminal to the anode, and + terminal to the cathode) not It will show nothing at all, as if there is a break there. If the multimeter shows something else, then most likely the diode is faulty and unusable.
Checking capacitors and resistors
Burnt resistors can be seen immediately - they turn black. Therefore, finding a burnt resistor is quite easy. As for capacitors, checking them is more difficult. First, as in the case of resistors, you need to inspect them. If they do not outwardly cause suspicion, then they should be unsoldered and checked using an LRC meter. Electrolytic capacitors usually fail. At the same time, they swell when they burn. Another reason for their failure is time. Therefore, in older devices, all electrolytic capacitors are often replaced.
Checking transistors
Transistors are tested similarly to diodes. First, an external inspection is carried out and if it does not cause suspicion, the transistor is checked using a multimeter. Only the multimeter terminals are connected alternately between the base-collector, base-emitter and collector-emitter. By the way, transistors have an interesting malfunction. When checked, the transistor is normal, but when it is connected to the circuit and power is supplied to it, after a while the circuit stops working. It turns out that the transistor has heated up and in a heated state behaves as if it were broken. This transistor should be replaced.
Electronics accompanies modern man 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 start
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 three types malfunctions.
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 Such testing of a suspect means replacing the block 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 exact location breakdowns. 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.
If mechanical components are worn out by friction, then 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. Moreover, it must be done before it is reset, acknowledged, or turned off! This is very important! Miss some important information- this 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 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. It doesn’t happen often, but it happens that they break through, and this breakdown is sometimes very hard to see, especially if the insulator is black. Due to their reactive properties, these plastics do not warp when exposed to high heat, which also makes it difficult to detect broken insulation.
Look for darkened insulation on the windings of relays, starters, and electric motors. Are there any darkened resistors or other electrical and 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.
Look to 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 of the switch are 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 and stepper motors. Move other mechanisms as necessary. Compare the force applied with other similar working devices, if of course there is such a possibility.
Inspect the insides of the device in operating condition - 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 located far beyond the boundaries 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 for a long time worked without maintenance, I recommend that before starting an in-depth troubleshooting, you do preventive maintenance on the contacts - lighten them with a regular eraser and wipe with alcohol. Attention! Never use abrasive sandpaper to clean silver-plated or gold-plated contacts. This is certain death for the connector. Plating with silver or gold is always done in a very thin layer, and it is very easy to erase it down to copper with an abrasive. It is useful to carry out the procedure for self-cleaning the contacts of the socket part of the connector, in the professional slang of “mother”: connect and disconnect the connector several times, the spring contacts are slightly cleaned from friction. I also advise that when working with any contact connections, do not touch them with your hands - oil stains from your fingers negatively affect the reliability of the electrical contact. Cleanliness is the key to reliable contact operation.
The first thing is to check the operation of any blocking or protection at the beginning of the repair. (In any normal technical documentation for the device there is a chapter with detailed description locks 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, short circuit in the power supply and in the power section, and others possible malfunctions, which can damage the working device. The opposite 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 search for a fault to a specific electrical element. This is the name of the method in which the repairman conducts an intelligent analysis of all the signals with which the tested node “lives”. Connect the unit, node, or board under study to the device using special extension cords-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 compare the signals at the control points on the board with the voltages and oscillograms on the diagram (in the documentation). If the diagram and documentation do not shine with such details, then rack your brains. Good knowledge of circuit design will come in handy here.
If you have any doubts, you can “hang” a working sample board from the working device on the adapter and compare the signals. Check with the diagram (with documentation) all possible signals, voltages, oscillograms. 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 bear 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. When it comes to repairs, it is very important to have a clear understanding of 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 This will always be appreciated 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've reached your climax this repair. 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 of the malfunction. 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 reasons occurrence of failures.
Bad contact (first of all!). Clean the connectors all at once throughout the entire device and carefully inspect the contacts while doing so.
Overheating (as well as hypothermia) of the entire device, caused by increased (low) ambient temperature, or caused by long work 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 in an efficient way repair is a method of replacing blocks with known good ones. When changing blocks and assemblies between identical devices, carefully ensure that they are completely identical. Please note availability personal settings they contain various potentiometers, customized inductance circuits, switches, jumpers, jumpers, software inserts, ROM with different versions firmware If there are any, then make the decision to replace after thinking everything over possible problems, which 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 to large number 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.
Checking electronic components using multimeter this is a pretty simple task. To carry it out, you need an ordinary Chinese-made multimeter, the purchase of which is not a problem, it is only important to avoid the cheapest, frankly low-quality models.
Analogue meters with a pointer indicator are still capable of performing such tasks, but are more convenient to use digital multimeters , in which the mode is selected using switches, and the measurement results are displayed on an electronic display.
Appearance of analog and digital multimeters:
Nowadays, digital multimeters are most often used, since they have a lower percentage of error, are easier to use, and the data is displayed directly on the device’s display.
The scale of digital multimeters is larger, there are convenient additional functions - temperature sensor, frequency meter, capacitor test, etc.
Transistor check
Without going into technical details, transistors can be field-effect and bipolar
A bipolar transistor consists of two counter diodes, so the test is performed according to the “base-emitter” and “base-collector” principle. The current can only flow in one direction, it should not be in the other. There is no need to check the emitter-collector junction. If there is no voltage at the base, but current still flows, the device is faulty.
To test an N-channel field-effect transistor, you need to connect the black (negative) probe to the drain terminal. A red (positive) probe is connected to the source terminal of the transistor. In this case, the transistor is closed, the multimeter displays a voltage drop of approximately 450 mV on the internal diode, and infinite resistance on the reverse. Now you need to attach the red probe to the gate, and then return it to the source terminal. The black probe remains connected to the drain terminal. Having shown 280 mV on the multimeter, the transistor opened when touched. Without disconnecting the red probe, touch the black probe to the shutter. Field effect transistor will close, and on the display of the multimeter we will see a voltage drop. The transistor is working properly, as these manipulations showed. Diagnostics of the P-channel transistor is performed in the same way, but the probes are swapped.
Diode check
Several main types of diodes are now produced (zener diode, varicap, thyristor, triac, light and photo diodes), each of them is used for specific purposes. To check the diode, the resistance is measured with a plus at the anode (should be from several tens to several hundred Ohms), then with a plus at the cathode - it should be infinity. If the indicators are different, the device is faulty.
Checking resistors
As you can understand from the picture, resistors are also different:
Manufacturers indicate the nominal resistance on all resistors. We measure it. A 5% error in the resistance value is allowed; if the error is greater, it is better not to use the device. If the resistor has turned black, it is also better not to use it, even if the resistance is within normal limits.
Checking capacitors
First we inspect the capacitor. If there are no cracks or swelling on it, you need to try (carefully!) Twist the capacitor leads. If you can turn it or even pull it out altogether, the capacitor is broken. If everything looks normal, we check the resistance with a multimeter; the readings should be equal to infinity.
Inductor
Failures in coils can be different. Therefore, we first rule out a mechanical fault. If there is no external damage, we measure the resistance by connecting the multimeter to the parallel terminals. It should be close to zero. If the nominal value is exceeded, there may be a breakdown inside the coil. You can try to rewind the coil, but it’s easier to change it.
Chip
There is no point in checking a microcircuit with a multimeter - they contain dozens and hundreds of transistors, resistors and diodes. The microcircuit must be free of mechanical damage, rust stains and overheating. If everything is fine externally, the microcircuit is most likely damaged internally and cannot be repaired. However, you can check the outputs of the microcircuit for voltage. Too low resistance of the power outputs (relative to the total) indicates short circuit. If at least one of the outputs is faulty, most likely the circuit cannot be returned to operation.