How to find a faulty element on the board. Troubleshooting Methods
Quantity electronic devices is growing every year at an unprecedented rate.
Thus, electronics production in St. Petersburg can only be encouraging. However, no matter how high its quality, it can still break. Sometimes a breakdown can be fixed on your own, so there is no need to take the equipment to a service center unnecessarily.
Where to begin
Correcting problems with electronic devices is a delicate thing, and to learn how to do it yourself, you need some knowledge of physics, at least a school course.
You should at least have an idea of what it is:
- current strength;
- metal resistance;
- inductance, etc.
You also need to gain experience in soldering radio components, and learn to use an electrical tester and multimeter. For repairs you will need to purchase everything necessary equipment, and depending on the type of equipment being repaired, you will need to understand electrical circuits.
A lot of people think that PC repair is a job for workshops. But even beginners can fix a computer at home without any special skills and with a minimum of equipment. You can replace the capacitors yourself, if you have a soldering iron. But if you need to replace microcircuits, if you do not have the experience and equipment, it is not advisable to repair such a breakdown yourself.
If the electronics do not turn on
When connected to electrical network the device does not work, no LED signals are activated or no sound is produced, the reason for this is a burnt-out power supply. Try connecting the device in series with a powerful incandescent lamp to prevent a short circuit. When the power supply is running, the lamp will not light up, but if there is a short circuit on the power supply, the lamp will light up.
Then we look for a fault in the power supply itself. It could be a simple cable break or a blown fuse. If successful, we fix the problem by replacing new parts or soldering broken ones.
Incorrect work
If your electronics work intermittently, periodically giving a problem, there are many reasons for this operation. For example, when the computer turns off when the computer is under load, and after some time it works again, the fault may lie in overheating or damaged contacts.
A situation often arises when, due to a small, insignificant part that has failed, it stops working. household appliance. Therefore, many novice radio amateurs would like to know the answer to the question of how to ring a board with a multimeter. The main thing in this matter is to quickly discover the cause of the breakdown.
Before performing an instrumental test, it is necessary to inspect the board for damage. Electrical diagram The board should be without damage to the bridges, the parts should not be swollen and black. Here are the rules for checking some elements, including the motherboard.
Checking individual parts
Let's look at a few parts, if they break, the circuit breaks down, and along with it all the equipment.
Resistor
This part is used quite often on various boards. And just as often, when they break down, the device malfunctions. It is easy to check resistors for functionality with a multimeter. To do this, it is necessary to measure the resistance. If the value tends to infinity, the part should be replaced. Part malfunction can be determined visually. As a rule, they turn black due to overheating. If the value changes by more than 5%, the resistor requires replacement.
Diode
Checking the diode for malfunction will not take much time. Turn on the multimeter to measure resistance. Red probe for the anode of the part, black for the cathode - the reading on the scale should be from 10 to 100 Ohms. We rearrange, now the minus (black probe) on the anode is a reading tending to infinity. These values indicate the health of the diode.
Inductor
The board rarely fails due to the fault of this part. As a rule, breakdown occurs for two reasons:
- turn short circuit;
- circuit break.
Having checked the coil resistance value with a multimeter, if the value is less than infinity, the circuit is not broken. Most often, the inductance resistance is several tens of ohms.
Determining a turn short is a little more difficult. To do this, we transfer the device to the circuit voltage measurement sector. It is necessary to determine the magnitude of the self-induction voltage. We apply a small voltage current to the winding (most often they use a crown), we close it with a light bulb. The light blinked - there was no circuit.
Plume
In this case, you should ring the input contacts on the board and on the cable itself. We insert the multimeter probe into one of the contacts and start ringing. If it goes sound signal, which means these contacts are working. If there is a malfunction, one of the holes will not find a “pair”. If one of the contacts rings with several at once, it means it’s time to change the cable, since there is a short circuit on the old one.
Chip
A wide variety of these parts are produced. It is quite difficult to measure and determine the malfunction of a microcircuit using a multimeter; pci testers are most often used. A multimeter does not allow you to take measurements, because one small part contains several dozen transistors and other radio elements. And in some the latest developments Billions of components are concentrated.
The problem can only be identified if visual inspection(case damage, discoloration, broken leads, extreme heat). If a part is damaged, it must be replaced. Often, when a microcircuit breaks down, the computer and other devices stop working, so the search for a breakdown should begin with examining the microcircuit.
Motherboard tester is best option failure detection individual part and node. By connecting POST card to the motherboard and launching the testing mode, we receive information about the breakdown node on the device screen. Even a beginner without any special skills can perform an examination with a pci tester.
Stabilizers
Every radio technician knows the answer to this question, how to check a zener diode. To do this, move the multimeter to the diode measurement position. Then we touch the probes to the outputs of the part and take readings. We swap the probes and take measurements and write down the numbers on the screen.
With one value of the order of 500 Ohms, and in the second measurement the resistance value tends to infinity - this part is serviceable and suitable for further use. On a faulty one, the value in two dimensions will be equal to infinity - with an internal break. With a resistance value of up to 500-hundred ohms, a semi-breakdown occurred.
But most often the bridges on the motherboard chip burn out - the north and south. These are power supply stabilizers for the circuits that supply voltage to the motherboard. This “trouble” is identified quite easily. Turn on the power supply on the computer and raise your hand to motherboard. It will become very hot at the site of the injury. One of the reasons for such a breakdown may be the field-effect transistor of the bridge. Then we carry out a continuity test on their terminals and, if necessary, replace the faulty part. The resistance in a working area should be no more than 600 Ohms.
Using the method of detecting a heating device, a short circuit (short circuit) is determined on some parts of the board. When power is applied and a heating area is detected, use a brush to lubricate the heating area. Based on the evaporation of alcohol, a part with a short circuit is determined.
So you go to the kettle to celebrate with the thought of slamming a mug of tea with a bagel in honor of what just happened. assembled device, but it suddenly stopped working. Wherein visible reasons no: 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 prevent 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. 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 switching(- terminal to the anode, and + terminal to the cathode) will not show anything 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. Firstly, 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.
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 are 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 attached 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. The field-effect transistor will close, and we will see a voltage drop on the multimeter display. 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 exclude mechanical failure. 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. There should not be on the chip mechanical damage, stains from rust 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.
Working with a digital multimeter
Like an analog tester, a digital tester has red and black probes, as well as 2-4 additional sockets. Traditionally, the "ground" or common terminal is marked black. The common output socket is indicated by a “-” (minus) sign or the COM code. The end of the output is sometimes equipped with an alligator clip for fastening to the circuit being tested.
The red lead always uses a socket marked "+" (plus) or code V. More complex multimeters have an additional socket for the red lead, labeled "VQmA". Its use allows you to measure resistance and voltage in milliamps.
The socket marked 10ADC is intended for measuring direct current, up to 10A.
The main mode switch, which has a round shape and is located in the middle of the front panel in most multimeters, serves to select measurement modes. When choosing a voltage, you should choose a mode greater than the current strength. If you need to check a household outlet, from two modes, 200 and 750 V, select mode 750.
In everyone's life home handyman who knows how to hold a soldering iron and use a multimeter, there comes a time when some complex electronic equipment and he is faced with a choice: take it to a service center for repairs or try to repair it himself. In this article we will look at techniques that can help him with this.
So, your equipment is broken, for example an LCD TV, where should you start repairing it? All craftsmen know that it is necessary to begin repairs not with measurements, or even immediately resolder the part that aroused suspicion of something, but with an external examination. This includes not only examining the appearance of the TV circuit boards, removing its cover, looking for burnt radio components, and listening to hear a high-frequency squeak or click.
We connect the device to the network
To begin with, you just need to turn on the TV to the network and see: how it behaves after turning it on, whether it responds to the power button, or the standby mode LED is blinking, or the image appears for a few seconds and disappears, or there is an image but there is no sound, or vice versa. Based on all these signs, you can obtain information from which you can build upon for further repairs. For example, by blinking an LED at a certain frequency, you can set a fault code, self-testing of the TV.
TV error codes by LED blinking
Once the signs have been established, you should look for schematic diagram devices, or better if a Service manual for the device, documentation with a diagram and a list of parts is issued, on special websites dedicated to electronics repair. It will also not be amiss in the future to enter the full name of the model into the search engine, with brief description breakdown, conveying in a few words its meaning.
Service manual
True, sometimes it is better to search for a diagram by the device chassis, or the name of the board, for example a TV power supply. But what if you still couldn’t find the circuit, and you are not familiar with the circuitry of this device?
Block diagram of LCD TV
In this case, you can try to ask for help from specialized specialists, after conducting a preliminary diagnosis yourself, in order to collect information from which the specialists helping you can build on. What stages does this preliminary diagnosis include? First, you must make sure that power is supplied to the board if the device does not show any signs of life at all. This may seem trivial, but it wouldn’t hurt to test the power cord for integrity using the audio test mode. how to use a regular multimeter.
Tester in audio mode
Then the fuse is tested in the same multimeter mode. If everything is fine here, we should measure the voltage at the power connectors going to the TV control board. Typically, the supply voltages present on the connector pins are labeled next to the connector on the board.
TV control board power connector
So, we measured and there is no voltage at the connector - this indicates that the circuit is not functioning correctly, and we need to look for the reason for this. Most common cause breakdowns encountered in LCD TVs are banal electrolytic capacitors, with an increased ESR equivalent series resistance. About ESR.
Capacitor ESR Table
At the beginning of the article, I wrote about a squeak that you may hear, and so its manifestation, in particular, is a consequence of the overestimated ESR of small-value capacitors located in the standby voltage circuits. To identify such capacitors, a special device is required, an ESR meter, or, in the latter case, the capacitors will have to be unsoldered for measurement. Photo of your ESR meter allowing you to measure this parameter I posted it below without soldering.
My ESR meter
What to do if such devices are not available, and suspicion falls on these capacitors? Then you will need to consult on repair forums and clarify in which node, which part of the board, the capacitors should be replaced with ones that are known to work, and only new (!) capacitors from a radio store can be considered as such, because used ones have this parameter, ESR may also be off the charts or already on the verge.
Photo - swollen capacitor
The fact that you could unsolder them from a device that previously worked in in this case does not matter, since this parameter is important only for operation in high-frequency circuits; accordingly, earlier, in low-frequency circuits, in another device, this capacitor could function perfectly, but have an ESR parameter that was very high. The work is greatly facilitated by the fact that high-value capacitors have a notch in their upper part, along which, if they become unusable, they are simply opened, or a swelling forms, a characteristic sign of their unsuitability for anyone, even a novice master.
Multimeter in Ohmmeter mode
If you see blackened resistors, you will need to test them with a multimeter in ohmmeter mode. First, you should select the 2 MOhm mode; if there are values on the screen that differ from unity, or the measurement limit is exceeded, we should accordingly reduce the measurement limit on the multimeter to establish its more accurate value. If there is one on the screen, then most likely such a resistor is broken and should be replaced.
Color coding of resistors
If it is possible to read its denomination from the ones printed on its body, it’s good, otherwise you can’t do without a diagram. If the circuit is available, then you need to look at its designation and set its rating and power. If the resistor is precision, its (precise) value can be set by connecting two ordinary resistors in series, a larger and a smaller value, the first we set the value roughly, the last we adjust the accuracy, while their total resistance will work out.
Transistors are different in the photo
Transistors, diodes and microcircuits: it is not always possible to determine the malfunction with them appearance. You will need to measure with a multimeter in audio testing mode. If the resistance of any of the legs, relative to some other leg, of one device, is zero, or close to it, in the range from zero to 20-30 Ohms, most likely such a part must be replaced. If this bipolar transistor, you need to call in accordance with the pinout, it p-n junction s.
Checking the transistor with a multimeter
Most often, such a check is enough to consider the transistor to be working. Better method. For diodes, we also cause a p-n junction, in the forward direction, there should be numbers of the order of 500-700 when measured, in the reverse direction one. The exception is Schottky diodes, they have a lower voltage drop, and when calling in the forward direction, the screen will show numbers in the range of 150-200, and in the reverse direction it will also be one. , field effect transistors, you can’t check this with a regular multimeter without soldering; you often have to consider them conditionally working if their terminals do not short-circuit with each other, or have low resistance.
Mosfet in SMD and regular housing
It should be taken into account that mosfets have a built-in diode between the Drain and the Source, and when dialing, the readings will be 600-1600. But there is one nuance here: if, for example, you ring the mosfets on the motherboard and hear a beep at the first touch, do not rush to write the mosfets into the broken one. Its circuits contain electrolytic filter capacitors, which, when charging begins, are known to behave for some time as if the circuit were short-circuited.
Mosfets on PC motherboard
This is what our multimeter shows, in audible dialing mode, with a squeak for the first 2-3 seconds, and then increasing numbers will appear on the screen, and the unit will be set as the capacitors charge. By the way, for the same reason, in order to save the diodes of the diode bridge, in pulse blocks power supply, a thermistor is installed that limits the charging currents of electrolytic capacitors at the moment of switching on, through a diode bridge.
Diode assemblies on the diagram
Many acquaintances of novice repairmen who seek remote advice from In contact with, it’s shocking - you tell them to ring the diode, they ring it and immediately say: it’s broken. Here, as a standard, an explanation always begins that you need to either lift, unsolder one leg of the diode, and repeat the measurement, or analyze the circuit and board for the presence of parallel-connected parts in low resistance. These are often the secondary windings of a pulse transformer, which are connected parallel to the terminals of the diode assembly, or in other words, a dual diode.
Parallel and series connection of resistors
Here it is best to remember once, the rule of such connections:
- At serial connection two or more parts, their total resistance will be greater than each one separately.
- And with a parallel connection, the resistance will be less than the smaller of each part. Accordingly, our transformer winding, which has a resistance of 20-30 Ohms at best, by shunting, imitates for us a “broken” diode assembly.
Of course, unfortunately, it is impossible to reveal all the nuances of repairs in one article. For preliminary diagnosis of most breakdowns, as it turned out, a conventional multimeter used in the voltmeter, ohmmeter, and audio test modes is sufficient. Often, if you have experience, in the event of a simple breakdown and subsequent replacement of parts, the repair is completed, even without a diagram, carried out by the so-called “scientific poking method”. Which, of course, is not entirely correct, but as practice shows, it works, and, fortunately, not at all as shown in the picture above). Successful repairs to everyone, especially for the Radio Circuits website - AKV.
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