When repairing equipment and assembling circuits, you always need to be sure that all elements are in good working order, otherwise you will waste your time. Microcontrollers can also burn out, but how can you check if there are no external signs: cracks on the case, charred areas, a burning smell, etc.? To do this you need:
Power supply with stabilized voltage;
Multimeter;
Oscilloscope.
Attention:
A complete check of all components of the microcontroller is difficult - the best way is to replace it with a known good one, or flash another program code with the existing one and check its execution. In this case, the program should include both checking all pins (for example, turning LEDs on and off after a given period of time), as well as interrupt circuits and other things.
Theory
This is a complex device containing multifunctional units:
power circuits;
registers;
inputs-outputs;
interfaces and so on.
Therefore, when diagnosing a microcontroller, problems arise:
The operation of obvious components does not guarantee the operation of other components.
Before you start diagnosing any integrated circuit, you need to read the technical documentation, to find it, write in a search engine a phrase like: “name of datasheet element”, alternatively - “atmega328 datasheet”.
On the first sheets you will see basic information about the element, for example, let's look at some points from the datasheet for the common 328 atmega, let's say we have it in a dip28 package. We need to find the pinouts of microcontrollers in different cases, let's look at the dip28 we're interested in.
The first thing we will pay attention to is that pins 7 and 8 are responsible for the power supply plus and the common wire. Now we need to find out the characteristics of the power circuits and the consumption of the microcontroller. Supply voltage is from 1.8 to 5.5 V, current consumption in active mode is 0.2 mA, in low-power mode - 0.75 µA, while a 32 kHz real-time clock is turned on. Temperature range from -40 to 105 degrees Celsius.
This information is enough for us to carry out basic diagnostics.
Main reasons
Microcontrollers fail, both due to uncontrollable circumstances and due to incorrect handling:
1. Overheating during operation.
2. Overheating when soldering.
3. Output overload.
4. Reversing the power supply.
5. Static electricity.
6. Bursts in power circuits.
7. Mechanical damage.
8. Exposure to moisture.
Let's look at each of them in detail:
1. Overheating may occur if you operate the device in a hot place, or if you place your design in a case that is too small. The temperature of the microcontroller can also be increased by too tight installation, incorrect layout of the printed circuit board, when there are heating elements next to it - resistors, power circuit transistors, linear power regulators. The maximum permissible temperatures of common microcontrollers range from 80-150 degrees Celsius.
2. If you solder with a soldering iron that is too powerful or hold the tip on the legs for a long time, you can overheat the MK. The heat will reach the crystal through the leads and destroy it or its connection to the pins.
3. Pin overload occurs due to incorrect circuit design and short circuits to ground.
4. Polarity reversal, i.e. supplying negative power to Vcc and positive to GND may be a consequence of incorrect installation of the IC on the printed circuit board, or incorrect connection to the programmer.
5. Static electricity can damage the chip, both during installation, if you do not use antistatic paraphernalia and grounding, and during operation.
6. If a failure occurs, the stabilizer breaks, or for some other reason the microcontroller is supplied with a voltage higher than permissible, it is unlikely to remain intact. This depends on the duration of the impact of the emergency.
7. Also, do not be too zealous when installing the part or disassembling the device, so as not to damage the legs and body of the element.
8. Moisture causes oxides, leading to loss of contacts and short circuits. Moreover, we are talking not only about direct contact of liquid with the board, but also about long-term operation in conditions with high humidity (near reservoirs and in basements).
Checking the microcontroller without tools
Start with an external inspection: the case must be intact, the soldering of the terminals must be flawless, without microcracks and oxides. This can be done even with a regular magnifying glass.
If the device does not work at all, check the temperature of the microcontroller; if it is heavily loaded, it may heat up, but not burn, i.e. The temperature of the case should be such that the finger can tolerate holding it for a long time. You can't do anything else without a tool.
Check if voltage is coming to the Vcc and Gnd pins. If the voltage is normal and you need to measure the current, it is convenient to cut the trace leading to the Vcc power pin, then you can localize the measurements to a specific microcircuit, without the influence of parallel-connected elements.
Do not forget to strip the board coating down to the copper layer in the place where you will touch the probe. If you cut it carefully, you can restore the track with a drop of solder or a piece of copper, for example from a transformer winding.
Alternatively, you can power the microcontroller from an external 5V power source (or other suitable voltage) and measure the consumption, but you still need to cut the track to eliminate the influence of other elements.
To carry out all measurements, we only need information from the datasheet. It will not be superfluous to look at what voltage the power stabilizer for the microcontroller is designed for. The fact is that different microcontroller circuits are powered by different voltages, it can be 3.3V, 5V and others. Voltage may be present, but may not be rated.
If there is no voltage, check if there is a short circuit in the power supply circuit or on the other legs. To quickly do this, turn off the power to the board, turn the multimeter into dial mode, and place one probe on the common wire of the board (ground).
Usually it runs along the perimeter of the board, and there are tinned areas at the mounting points with the housing or on the connector housings. And with the second one, pass through all the pins of the microcircuit. If it beeps somewhere, check what kind of pin it is, the dialing should work on the GND pin (8th pin on atmega328).
If it doesn’t work, the circuit between the microcontroller and the common wire may be broken. If it works on other legs, look at the diagram to see if there are any low-resistance resistances between the pin and the minus. If not, you need to unsolder the microcontroller and ring again. We check the same thing, but now between the power supply positive (with the 7th pin) and the microcontroller pins. If desired, all legs are connected to each other and the connection diagram is checked.
The eyes of an electronics engineer. With its help you can check the presence of generation on the resonator. It is connected between pins XTAL1,2 (pins 9 and 10).
But the oscilloscope probe has a capacitance, usually 100 pF; if you set the divider to 10, the probe capacitance will drop to 20 pF. This makes changes to the signal. But for testing functionality this is not so important; we need to see if there are any fluctuations at all. The signal should have a shape like this, and a frequency corresponding to a specific instance.
If the circuit uses external memory, then you can check it very easily. There must be bursts of rectangular pulses on the data exchange line.
This means that the microcontroller is properly executing code and exchanging information with memory.
If you unsolder the microcontroller and connect it to the programmer, you can check its response. To do this, in the program on your PC, click the Read button, after which you will see the programmer ID; on the AVR you can try to read the fuses. If there is no read protection, you can read the firmware dump, load another program, test the work on the code you know. This is an effective and simple way to diagnose microcontroller faults.
The programmer can be either specialized, such as USBASP for the ATS family:
And universal, like Miniprog.
Conclusion
As such, testing a microcontroller is no different from testing any other microcircuit, except that you have the opportunity to use a programmer and read the microcontroller information. This will ensure that it can communicate with your PC. However, there are faults that cannot be detected in this way.
In general, the control device rarely fails; more often the problem lies in the wiring, so you should not immediately go to the microcontroller with all the tools; check the entire circuit so as not to have problems with subsequent firmware.
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 on the multimeter display 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 common) indicates a 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.
Checking the serviceability of an integrated circuit begins with measuring direct and pulse voltages at their terminals. To avoid accidental short circuits of closely spaced pins of the microcircuit, it is recommended to connect the probes of measuring instruments not to these pins, but to the printed conductors connected to them or to a radio element. If the measurement results differ from the required ones, then the cause should be established: defects in the radioelements connected to the integrated circuit, deviation of their values from the nominal values, the source from which the necessary pulse and direct voltages come, or a malfunction of the integrated circuit itself.
It is impossible to check the serviceability of an integrated circuit by replacement if for this purpose it must be soldered from the printed circuit board.
To facilitate dismantling, it is recommended that the integrated circuit be installed on the board with a gap of at least 3 mm between the housings, as well as between the integrated circuit and the board. When performing electrical installation of an integrated circuit, precautions must be taken.
Installation of the integrated circuit should be carried out on a table whose surface is covered with cotton material or antistatic linoleum. The working tool (rod) of the soldering iron and the body (common bus) of the radio device should be grounded or the electric soldering iron should be connected to the network through a transformer, since during soldering the occurrence of leakage currents between the rod of the soldering iron connected to the network and the terminals of the integrated circuit can lead to its failure .
It is advisable to solder an integrated circuit using a special group electric soldering iron to simultaneously warm up all its terminals. Soldering time should be no more than 3s. Alternate soldering of leads is allowed. In this case, the interval between soldering adjacent terminals must be at least 10 s. For soldering the terminals of an integrated circuit, solders of the POSK-50-18 or POS-61 brand are used.
In general, the program for setting up and testing electronic systems of machine tools with electronic control systems includes the following elements of work.
1. External inspection.
2. Checking the correct inclusion of elements in the diagram and checking their installation.
3. Electrical strength insulation test and insulation resistance measurement.
4. Measuring the magnitudes and shapes of voltages and currents in electronic circuit elements.
5. Reading performance characteristics (gain, signal distortion, signal edge, etc.).
6. Control load of the circuit on the actuator or its equivalent.
7. Recording the measurement results and the test performed in a special card.
If during testing, deviations from the required parameters exceeding the permissible values are revealed, then it is necessary to identify the cause of the deviation and eliminate the malfunction.
As mentioned above, the most appropriate method for setting up and testing ESP electronic units is to carry out this work outside the machine on special stands.
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Checking radio components with a multimeter
Checking parts with an analog multimeter.
You cannot do without a measuring device, because... will have to check resistor resistance, voltage and current in different circuits of structures. Measuring device, among the people - ohmmeter, avometer(amp-volt-ohmmeter), tester or multimeter(from the English multimeter - a measuring device that combines several functions) - everyone should have. Nowadays they are very popular digital devices. They are multifunctional and relatively inexpensive. Previously, they were widely used as a measuring instrument. analog testers with dial indicator(see Fig. 1).
Not all beginners know that You can check almost all radio elements with an ohmmeter: resistors, capacitors, inductors, transformers, diodes, thyristors, transistors, some microcircuits. In an avometer, the ohmmeter is formed by an internal current source (dry cell or battery), a pointer device and a set of resistors that switch when the measurement limits change. The resistances of the resistors are selected in such a way that when the ohmmeter terminals are short-circuited, the instrument needle deviates to the right to the last scale division. This division corresponds to the zero value of the measured resistance. When the ohmmeter terminals are open, the arrow of the device is opposite the leftmost division of the scale, which is indicated by the symbol of infinitely large resistance. If some resistance is connected to the ohmmeter terminals, the arrow shows an intermediate value between zero and infinity, and the reading is made according to the digitization of the scale. Due to the fact that ohmmeter scales are made on a logarithmic scale, the edges of the scale are compressed. That's why The greatest measurement accuracy corresponds to the position of the arrow in the middle, stretched part of the scale. Thus, if the instrument needle is at the edge of the scale, in its compressed part, to increase the reading accuracy, you should switch the ohmmeter to another measurement limit.
Ohmmeter makes a measurement resistance connected to its terminals by measuring the direct current flowing in the measuring circuit. Therefore, a constant voltage is applied to the measured resistance from a source built into the ohmmeter. Due to the fact that some parts have different resistance to direct current depending on the polarity of the applied voltage, to use the ohmmeter correctly, you need to know which of the ohmmeter terminals is connected to the positive of the current source, and which to the negative. This information is usually not indicated in the avometer passport, and you need to determine it yourself. This can be done either using an avometer circuit, or experimentally using some additional voltmeter or a working diode of any type. The ohmmeter probes are connected to the voltmeter so that the voltmeter needle deviates to the right from zero. Then the probe that is connected to the positive of the voltmeter will also be positive, and the second one will be negative. When using a diode for this purpose, its resistance is measured twice; first, randomly connecting probes to the diode, and the second time - vice versa. The basis is the measurement at which the ohmmeter readings are smaller. In this case, the probe connected to the anode of the diode will be positive, and the probe connected to the cathode of the diode will be negative.
When checking the serviceability For any given radio element, two different situations are possible: either an isolated, separate element must be tested, or an element soldered into some device. It must be taken into account that, with rare exceptions, checking an element soldered into the circuit will not be complete; such checking may result in gross errors. They are due to the fact that other elements in the circuit may be connected in parallel to the controlled element, and the ohmmeter will measure not the resistance of the element being tested, but the resistance of its parallel connection with other elements. The possibility of reliably assessing the health of a monitored circuit element can be assessed by studying this circuit, checking what other elements are connected to it and how they can affect the measurement result. If it is difficult or impossible to make such an assessment, you should unsolder at least one of the two terminals of the controlled element from the rest of the circuit and only then check it. At the same time, we should also not forget that the human body also has some resistance, depending on the humidity of the skin surface and other factors. Therefore, when using an ohmmeter, in order to avoid measurement errors, you should not touch both terminals of the element being tested with your fingers.
Checking resistors
Checking fixed resistors is done with an ohmmeter by measuring their resistance and comparing it with the nominal value, which is indicated on the resistor itself and on the circuit diagram of the device. When measuring the resistance of a resistor, the polarity of connecting the ohmmeter to it does not matter. It must be remembered that the actual resistance of the resistor may differ from the nominal value by a tolerance value. Therefore, for example, if a resistor with a nominal resistance of 100 kOhm and a tolerance of ±10% is tested, the actual resistance of such a resistor can range from 90 to 110 kOhm. In addition, the ohmmeter itself has a certain measurement error (usually about 10%). Thus, if the actually measured resistance deviates by 20% from the nominal value, the resistor should be considered serviceable.
1. In general, where is which dipstick is indicated on the body of any avometer.
2. If it is not torn, then it is in good working order and can always be useful.
When checking variable resistors the resistance between the extreme terminals is measured, which must correspond to the nominal value, taking into account the tolerance and measurement error, and it is also necessary to measure the resistance between each of the extreme terminals and the middle terminal. These resistances, when rotating the axis from one extreme position to another, should change smoothly, without jumps, from zero to the nominal value. When checking a variable resistor soldered into the circuit, two of its three terminals must be unsoldered. If a variable resistor has additional taps, it is acceptable for only one lead to remain soldered to the rest of the circuit.
Checking capacitors
Basically capacitors may have the following defects : breakage, breakdown and increased leakage. The breakdown of a capacitor is characterized by the presence of a short circuit between its terminals, that is, zero resistance. Therefore, a broken capacitor of any type is easily detected with an ohmmeter by checking the resistance between its terminals. The capacitor does not pass direct current; its resistance to direct current, which is measured with an ohmmeter, must be infinitely large. However, this turns out to be true only for an ideal capacitor. In reality, between the plates of a capacitor there is always some kind of dielectric with a finite resistance value, which is called leakage resistance. This is what is measured with an ohmmeter. Depending on the dielectric used in the capacitor, serviceability criteria are established based on the leakage resistance. Mica, ceramic, film, paper, glass and air capacitors have very high leakage resistance, and when tested, an ohmmeter should show an infinite resistance. However, there is a large group of capacitors whose leakage resistance is relatively small. This includes all polar capacitors that are designed for a certain polarity of the voltage applied to them, and this polarity is indicated on their cases. When measuring the leakage resistance of this group of capacitors, it is necessary to observe the polarity of the ohmmeter connection (the positive terminal of the ohmmeter must be connected to the positive terminal of the capacitor), otherwise the measurement result will be incorrect. This group of capacitors primarily includes all electrolytic capacitors and oxide semiconductor capacitors. The leakage resistance of serviceable capacitors of this group must be at least 100 kOhm, for the rest - at least 1 MOhm. When checking high-capacity capacitors, you need to take into account that when you connect an ohmmeter to the capacitor, if it has not been charged, it begins charging, and the ohmmeter needle shoots towards the zero scale value. As charging progresses, the arrow moves towards increasing resistance. The larger the capacitor capacity, the slower the needle moves. The leakage resistance should be measured only after it has practically stopped. When testing capacitors with a capacity of about 1000 µF, this may take several minutes. An internal break or partial loss of capacitance in a capacitor cannot be detected by an ohmmeter; this requires a device that allows you to measure the capacitance of the capacitor. However, a break in a capacitor with a capacity of more than 0.2 μF can be detected with an ohmmeter by the absence of an initial jump in the needle during charging. It should be noted that re-checking the capacitor for an open circuit based on the absence of an initial jump in the needle can be done only after removing the charge, for which the capacitor terminals must be short-circuited for a short time.
Variable capacitors are checked ohmmeter to check for short circuits. To do this, an ohmmeter is connected to each section of the unit and the axis is slowly rotated from one extreme position to another. The ohmmeter should show infinite resistance at any axis position.
Checking inductors
When checking inductors An ohmmeter is used to check only the absence of a break in them. The resistance of single-layer coils should be zero, the resistance of multi-layer coils is close to zero. Sometimes the device's passport data indicates the resistance of multilayer coils to direct current and its value can be used as a guide when checking them. If the coil breaks, the ohmmeter shows an infinitely high resistance. If the coil has a tap, you need to check both sections of the coil by connecting an ohmmeter first to one of the outermost terminals of the coil and to its tap, and then to the second extreme terminal and tap.
Checking low-frequency chokes and transformers
As a rule, the data sheets of the equipment or the instructions for its repair indicate the values of the resistance of the DC windings, which can be used when testing transformers and chokes. A winding break is detected by an infinitely high resistance between its terminals. If the resistance is significantly less than the nominal value, this may indicate the presence of short-circuited turns. However, most often short-circuited turns occur in small quantities when a short circuit occurs between adjacent turns and the winding resistance changes slightly. To check the absence of short-circuited turns, you can proceed as follows. The winding with the largest number of turns is selected from the transformer, and an ohmmeter is connected to one of the terminals using an alligator clip. The second terminal of this winding is touched with a slightly damp finger of the left hand. Holding the metal tip of the second ohmmeter probe with your right hand, connect it to the second terminal of the winding without lifting the finger of your left hand from it. The ohmmeter needle deviates from its initial position, indicating the winding resistance. When the arrow stops, move your right hand with the probe away from the second terminal of the winding. At the moment the circuit breaks, with a working transformer, a slight electric shock is felt that occurs when the circuit breaks. Due to the fact that the discharge energy is negligible, such a test does not pose any danger. In this case, the ohmmeter must be used at the lowest measuring limit, which corresponds to the highest measuring current.
Diode check
Semiconductor diodes are characterized by a sharply nonlinear current-voltage characteristic. Therefore, their forward and reverse currents at the same applied voltage are different. This is the basis for checking diodes with an ohmmeter. Forward resistance is measured by connecting the positive terminal of the ohmmeter to the anode, and the negative terminal to the cathode of the diode. A broken diode has zero forward and reverse resistances. If the diode is open, both resistances are infinitely large.
It is impossible to indicate in advance the values of forward and reverse resistance or their ratio, since they depend on the applied voltage, and this voltage is different for different avometers and at different measurement limits. However, a working diode should have a reverse resistance greater than its forward resistance. The ratio of reverse to forward resistance for diodes designed for low reverse voltages is high (can be more than 100). For diodes designed for high reverse voltages, this ratio turns out to be insignificant, since the reverse voltage applied to the diode by an ohmmeter is small compared to the reverse voltage for which the diode is designed. The technique for checking zener diodes and varicaps does not differ from that described. As you know, if a voltage of zero is applied to a diode, the diode current will also be zero. To obtain forward current, it is necessary to apply some threshold small voltage to the diode. Any ohmmeter provides the application of such voltage. However, if several diodes are connected in series and in accordance (in one direction), the threshold voltage required to unlock all diodes increases and may be greater than the voltage at the ohmmeter terminals. For this reason, it is impossible to measure the forward voltage of diode columns or selenium columns using an ohmmeter.
Checking thyristors.
Uncontrolled thyristors (dinistors) can be tested in the same way as diodes, if the dinistor trigger voltage is less than the voltage at the ohmmeter terminals. If it is larger, the dinistor does not unlock when the ohmmeter is connected and the ohmmeter shows a very high resistance in both directions. However, if the dinistor is broken, the ohmmeter registers this with zero readings of forward and reverse resistance. To test controlled thyristors (thyristors), the positive terminal of the ohmmeter is connected to the anode of the thyristor, and the negative terminal is connected to the cathode. The ohmmeter should show a very high resistance, almost equal to infinite. Then the terminals of the anode and the control electrode of the thyristor are short-circuited, which should lead to a sharp decrease in resistance, since the thyristor is unlocked. If you then disconnect the control electrode from the anode without breaking the circuit connecting the SCR anode to the ohmmeter, for many types of SCRs the ohmmeter will continue to show a low resistance of the open SCR. This occurs in cases where the anode current of the thyristor is greater than the so-called holding current. The thyristor must remain open if the anode current is greater than the guaranteed holding current. This requirement is sufficient, but not necessary. Individual instances of thyristors of the same type may have holding current values significantly less than the guaranteed one. In this case, the SCR remains open when the control electrode is disconnected from the anode. But if at the same time the thyristor is locked and the ohmmeter shows a high resistance, one cannot assume that the thyristor is faulty.
Checking transistors.
The equivalent circuit of a bipolar transistor consists of two diodes connected opposite each other. For pnp transistors, these equivalent diodes are connected by cathodes, and for npn transistors, by anodes. Thus, checking a transistor with an ohmmeter comes down to checking both p-n junctions of the transistor: collector-base and emitter-base. To check the direct resistance of the pnp transistor junctions, the negative terminal of the ohmmeter is connected to the base, and the positive terminal of the ohmmeter is connected alternately to the collector and emitter. To check the reverse resistance of the junctions, the positive terminal of the ohmmeter is connected to the base. When checking n-p-n transistors, the connection is made in reverse: forward resistance is measured when connected to the base of the positive terminal of the ohmmeter, and reverse resistance is measured when connected to the base of the negative terminal. When a junction breaks down, its forward and reverse resistances turn out to be zero. When a junction breaks, its direct resistance is infinitely large. In serviceable low-power transistors, the reverse transition resistances are many times greater than their forward resistances. For powerful transistors, this ratio is not so great, however, an ohmmeter allows you to distinguish them. From the equivalent circuit of a bipolar transistor it follows that using an ohmmeter you can determine the type of conductivity of the transistor and the purpose of its terminals (pinout). First, the type of conductivity is determined and the base terminal of the transistor is found. To do this, one terminal of the ohmmeter is connected to one terminal of the transistor, and the other terminal of the ohmmeter
touch in turn the other two terminals of the transistor. Then the first terminal of the ohmmeter is connected to the other terminal of the transistor, and the other terminal of the ohmmeter touches the free terminals of the transistor. Then the first terminal of the ohmmeter is connected to the third terminal of the transistor, and the other terminal touches the rest. After this, swap the ohmmeter leads and repeat the indicated measurements. You need to find a connection for the ohmmeter in which the connection of the second terminal of the ohmmeter to each of the two terminals of the transistor, not connected to the first terminal of the ohmmeter, corresponds to a small resistance (both junctions are open). Then the terminal of the transistor to which the first terminal of the ohmmeter is connected is the base terminal. If the first terminal of the ohmmeter is positive, then the transistor is of n-p-n conductivity, if it is negative, then it is of p-n-p conductivity. Now we need to determine which of the two remaining terminals of the transistor is the collector terminal. To do this, an ohmmeter is connected to these two terminals, the base is connected to the positive terminal of the ohmmeter for an npn transistor or to the negative terminal of the ohmmeter for a pnp transistor, and the resistance is noted, which is measured with an ohmmeter. Then the ohmmeter leads are swapped (the base remains connected to the same ohmmeter lead as before) and the resistance on the ohmmeter is again noticed. In the case where the resistance is less, the base was connected to the collector of the transistor.
Checking parts with a digital multimeter.
The main difference between a digital device and an analog one is is that the measurement results are displayed on a liquid crystal display. In addition, digital multimeters have higher accuracy and are easy to use, because you don’t have to understand all the intricacies of grading the measuring scale, as with dial measuring instruments.
Digital tester(see Fig. 1), like the analog one, has two probes - black and red, and from two to four sockets. The black pin is common (ground). The socket for the common output is marked as COM or simply “-” (minus), and the output itself at the end often has a so-called crocodile, so that during measurements it can be hooked to the ground of the electronic circuit. The red lead is inserted into the socket marked with voltage symbols - “V” or “+” (plus).
If your device contains more than two sockets, for example, as in Fig. 1, the red probe is inserted into the “VQmA” socket. This inscription means that you can measure voltage, resistance and small current - in milliamps. The socket, positioned slightly higher, marked 10ADC indicates that you can measure high direct current, but not higher than 10A.
The multimeter switch allows you to select one of several measurement limits.
To measure DC voltage, select DCV1 mode; if ACV is variable, connect the probes and look at the result. In this case, on the switch scale you must select a higher voltage than the one being measured. For example, you need to measure the voltage in an electrical outlet. In your device, the ACV scale consists of two parameters: 200 and 750 (these are volts). This means that you need to set the switch arrow to parameter 750 and you can safely measure the voltage.
1 DC – direct current (Direct Current), AC – alternating current (Alternating Current).
Current is measured serial connection of the multimeter into the electrical circuit. For example, you can take a regular light bulb from a flashlight and connect it in series with the device to a 5V adapter. Current will flow through the circuit and the light will light up, the device will display the current value.
Resistance on the device indicated by an icon that looks a bit like headphones. To measure resistance, the resistor must be unsoldered from the electrical circuit at least on one end to ensure that no other components in the circuit affect the result. We connect the probes to the two ends of the resistor and compare the ohmmeter readings with the value indicated on the resistor itself. It is also worth considering the magnitude of the tolerance (possible deviations from the norm), i.e. if according to the marking the resistor is 200 kOhm and has a tolerance of ± 15%, its actual resistance can be in the range of 170-230 kOhm.
Checking variable resistors, we first measure the resistance between the extreme terminals (must correspond to the resistor value), and then connect the multimeter probe to the middle terminal, alternately with each of the extreme ones. When the axis of the variable resistor is rotated, the resistance should change smoothly, from zero to its maximum value; in this case, it is more convenient to use an analog multimeter by observing the movement of the needle than by quickly changing numbers on the LCD screen.
To check diodes typical devices contain a special mode. In cheaper testers, you can use the dialing mode. Everything is simple here: the diode rings in one direction, but not in the other. You can also check the diode in resistance mode. To do this, set the switch to 1k0m. When you connect the red lead of the multimeter to the anode of the diode, and the black lead to the cathode, you will see its direct resistance; when connected in reverse, the resistance will be so high that at this measurement limit you will not see anything. If a diode is broken, its resistance in any direction will be zero; if it is broken, then its resistance in any direction will be infinitely large.
Conventional bipolar transistor consists of two diodes connected towards each other. Knowing how diodes are tested, it is easy to test such a transistor. It is worth remembering that transistors come in different types: in p-p-r conventional diodes are connected by cathodes, in p-p-p - by anodes. To measure the direct resistance of transistor pnp junctions, the minus of the multimeter is connected to the base, and the plus alternately to the collector and emitter. When measuring reverse resistance, we change the polarity. To test p-p-n transistors, we do the opposite. To put it even more briefly, the base-collector and base-emitter transitions should be connected in one direction, but not in the other.
To measure the gain of a transistor In terms of current, we use the hEF mode, if your device has it. The connector into which the transistor contacts are inserted to measure hEF is not of very high quality in almost all tester models and is set quite deep. That is, the legs of the transistor sometimes do not reach them. As a way out, insert single-core wires and touch them with the terminals of the transistor.
On digital multimeters The measurement limits are usually greater, and additional functions are often added, such as a frequency meter, a capacitance meter, and even a temperature sensor. But more expensive tester models have such capabilities. In addition, in expensive models there is no need to switch the measurement scale. Just set the switch to measure capacitance, resistance, etc., and the device shows the result.
To ensure that the multimeter does not fail when measuring voltage or current, especially if their value is unknown, it is advisable to set the switch to the highest possible measurement limit, and only if the reading is too small, to obtain a more accurate result, switch the multimeter to a lower limit current.
It was necessary to assemble input stabilizing power supply circuits for a device based on the PIC16F628 microcontroller that operates stably at a voltage of 5 volts. It is not difficult. I took the PJ7805 integrated circuit and made it based on it in accordance with the circuit from the datasheet. I applied voltage and got 4.9 volts at the output. Most likely, this is quite enough, but stubbornness, mixed with pedantry, took over.
I took out a box of integral stabilizers and set out to try on all the corresponding ones. And so as not to make a mistake, I even laid out the corresponding diagram in front of me. However, the enthusiasm ended already at the very first component. This “hedgehog without arms, without legs” made of connecting wires with crocodiles wanted to live his own life and obeyed the will of the radio amateur with great difficulty. Moreover, the tested stabilizer at the output showed 4.86 volts, which plunged my optimism into despondency.
No, something more significant is needed here, for example, some kind of sample, albeit simple, but nevertheless, or something. I typed it into the Yandex search engine and got what you see in the photo “Complex for monitoring integrated voltage stabilizers.” Well, this is not for the average amateur radio mind. It became clear that the wheel would have to be reinvented.
The diagram drawn up is clearly inferior to the top picture, well, there’s nothing we can do about it. Capacitor C1 eliminates generation when the input voltage is switched on intermittently, C2 serves to protect against transient noise pulses. I decided to take their capacity 100 µF. Voltage in accordance with the voltage of the stabilizer being tested. Place the capacitors as close to the housing of the integrated stabilizer as possible. Diode VD1 1N4148 will not allow the capacitor at the output of the stabilizer to discharge through it after switching off (this can lead to failure of the stabilizer). U In. integral stabilizer must be higher than U Out. at least 2.5 volts. The load should also be selected in accordance with the capabilities of the stabilizer being tested.
For the role of the housing, a homemade version was chosen, equipped with contact pins for connecting to a multimeter (minus in the “com” socket, plus in “V”). A triple pin contact like this can be used as a connecting element between the terminals of the component being tested and the circuit. My task is to test three-terminal integrated stabilizers designed for a voltage of no more than 12 volts, so I will put two 100 uF x 16 V capacitors into the circuit. A diode according to the circuit.
We insert them into the holes drilled exactly in accordance with the diameter of the pin contacts, from the inside we put a corresponding (small) metal washer on each pin, moisten it with active flux and press tightly, solder each washer to the corresponding pin, preventing the pin-washer pairs from connecting to each other . To do this, the washers need to be sharpened, the central one on both sides, the outer ones on one side. Holes at the installation location are required
just drill, if you pierce with an awl, an internal unevenness of the edges of the hole will form and it will not be possible to install the washer evenly + tightly. The pins, for strength, must also be located on a common solid dielectric base.
The contact pads formed by the soldering point of the pins and washers become the installation site for the circuit components. It turns out compact, and also follows the recommendation of the minimum distance of capacitors from the terminals of the integrated stabilizer being tested. With the connecting wires everything is simple, the main thing is to take them in the appropriate color (for “+” red, for “-” black) and there will be no confusion.
After some thought, I installed a push-action power button, placed in the gap of the positive (red) wire at the power input. Still, this is a necessary convenience. The triple pin contact needed to be “modified” - bent a little, here it is, either once the contacts were adjusted to fit the component leads, or before each connection the legs of the stabilizers were bent to fit the contacts.
The probe - the attachment for the multimeter is ready. I insert the probe pins into the corresponding sockets of the multimeter, set the measurement limit to 20 volts of direct voltage, connect the electrical current supply wires to the laboratory power supply in accordance with their layout, install a stabilizer for testing (I got it at 10 volts), respectively set the voltage on the power supply to 15 volts and I press the power button on the probe. The device worked, the display showed 9.91 V. Then, within a minute, I figured out all the three-terminal stabilizers for voltages up to 12 volts inclusive. Several of those carefully preserved turned out to be unusable.
Total
It has long been clear that such simple probes - attachments in amateur radio are just as necessary as very serious measuring instruments, but making them (tinkering with their manufacture) is simply too lazy, but in vain, and the understanding of this comes every time this simple device nevertheless, it was collected and provided invaluable assistance in creative endeavors. Author - Babay iz Barnaula.
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