How to replace a variable resistor. A simple scheme for replacing a variable resistor with two buttons (KP301, KP304). Marking of SMD elements
VAZ cars are very popular among drivers due to their decent technical characteristics, price-quality ratio, and excellent maintainability. Most malfunctions that occur during operation can be corrected by the driver independently without the help of professionals.
In this article we will talk about, which is one of the weak points in domestically produced cars, namely, we will look at how to replace a failed VAZ-2110 heater resistor.
Functions and purpose of the resistor
A resistor is often used in many vehicle electrical circuits. Its main function is the control and distribution of the supplied current to the element of its consumption, in this case to the car’s stove.
In cars, the source of current is the battery, which generates the necessary electrical charge for the functioning of all electrical elements of the vehicle. The resistor, in turn, transforms the current into the required voltage limits for the uninterrupted operation of a particular part. If the current converter becomes unusable, then more voltage will be supplied to the stove than is required for its operation and will not work. Also, high voltage can cause burnout of heater parts that operate on current.
The functionality of the part is simple. Initially, the current is generated in the car battery and supplied to the heater resistor. It transforms it into the required voltage value for high-quality operation of the heater.
The reasons for the failure of the converter may be heavy loads on it in case of long-term operation of the stove at maximum speed, or faulty wiring. As well as the quality of the resistor and suitability for the destination, it affects its service life.
Methods for diagnosing the health of a heater resistor
There are cases when the vehicle heater stops working at reduced speeds and functions only in enhanced mode. This is the main indicator of resistor failure.
The fact is that the VAZ-2110 is equipped with a current converter, which is equipped with two spirals. The first of them has a resistance of 0.23 Ohm and is responsible for the operation of the stove at the first speed, the second spiral with a resistance of 0.82 Ohm makes it possible to turn on the average speed of the stove. If a part malfunctions, only the maximum interior heating mode is switched on.
An additional vehicle resistor is directly responsible for the ability to switch heater speeds, therefore, if only at maximum mode, then it is necessary to replace the current converter.
Do-it-yourself replacement of a VAZ-2110 heater resistor
In order to replace the resistor, it is important to understand where exactly it is located. The part is located on the right side of the stove behind the vacuum booster. The first step before starting work is to disconnect the battery from the power supply; to do this, remove the negative wire from the terminal.
Further work is carried out inside the car. Initially, it is necessary to dismantle the windshield trim and trim. After this, the soundproofing padding on the right side of the machine panel is removed. To gain good access to the converter, the vacuum booster must be removed.
An additional heater resistor came into view. Next, you should disconnect the block with wiring from the contacts of the converter. Remember exactly how it is connected so that you can reassemble it correctly when you're done. The block can only be connected in one position.
Before you start replacing the product, you need to check its operation using an ohmmeter. There is no need to remove it to check the functionality of the part. Connect the contacts of the converter and ohmmeter in series, first on the first spiral, then on the second. If the resistance values differ significantly from the optimal value for correct operation of the device, then the product must be replaced.
Often the cause of part failure is the disconnection of the fuse located on the resistor board. Theoretically, you can extend the life of the element by soldering it in place. However, such work is characterized by significant difficulties, since it is very inconvenient to get to the fastening of the fuse contacts due to the very small distance between the board and the converter itself.
The price of a high-quality resistor is not very high, so the correct solution would be to replace it with a new part. Before replacing, purchase a new product from a specialized store. Do not buy parts secondhand or in spontaneous markets. Only a high-quality product can guarantee uninterrupted operation of the heating system of the car interior. The VAZ-2110 is equipped with a product with identification value RDO 2110-8118022-01. Buy products that match your car make, this will ensure correct current conversion and correct operation of the interior heating system.
To dismantle the product, you need to unscrew the fastening screw using a Phillips screwdriver. The failed part is carefully removed and a new converter is installed in its place. At this point the replacement can be considered completed. All that remains is to connect the block and connectors in place, and install the windshield trim in the reverse order.
Replace the resistor immediately after identifying its malfunction.
Operating a car stove after a breakdown of the additional current converter can lead to very serious problems. Very often it continues to function at maximum speed. In the cold season, drivers may not attach any importance to the malfunction and use the stove, despite the breakdown of the converter.
Prolonged operation of the heater at high speeds can cause the heater motor to burn out or the car wiring to catch fire due to the passage of high voltage through devices that operate on current.
Let's sum it up
One of the important elements that affects the functionality of a car heater is a resistor. It performs the important function of distributing current from the battery to the electric elements of the heater. If a problem with the operation of the current converter is detected, the product must be replaced.
Do not ignore the malfunction of parts that relate to current - this may be unsafe for your life. Immediately after identifying a problem, eliminate its cause.
(fixed resistors), and in this part of the article we’ll talk about, or variable resistors.
Variable resistance resistors, or variable resistors are radio components whose resistance can be change from zero to nominal value. They are used as gain controls, volume and tone controls in sound-reproducing radio equipment, are used for precise and smooth adjustment of various voltages and are divided into potentiometers And tuning resistors.
Potentiometers are used as smooth gain controls, volume and tone controls, serve for smooth adjustment of various voltages, and are also used in tracking systems, in computing and measuring devices, etc.
Potentiometer called an adjustable resistor having two permanent terminals and one movable. The permanent terminals are located at the edges of the resistor and are connected to the beginning and end of the resistive element, forming the total resistance of the potentiometer. The middle terminal is connected to a movable contact, which moves along the surface of the resistive element and allows you to change the resistance value between the middle and any extreme terminal.
The potentiometer is a cylindrical or rectangular body, inside of which there is a resistive element made in the form of an open ring, and a protruding metal axis, which is the handle of the potentiometer. At the end of the axis there is a current collector plate (contact brush) that has reliable contact with the resistive element. Reliable contact of the brush with the surface of the resistive layer is ensured by the pressure of a slider made of spring materials, for example, bronze or steel.
When the knob is rotated, the slider moves along the surface of the resistive element, as a result of which the resistance changes between the middle and extreme terminals. And if voltage is applied to the extreme terminals, then an output voltage is obtained between them and the middle terminal.
The potentiometer can be schematically represented as shown in the figure below: the outer terminals are designated by numbers 1 and 3, the middle one is designated by number 2.
Depending on the resistive element, potentiometers are divided into non-wire And wire.
1.1 Non-wire.
In non-wire potentiometers, the resistive element is made in the form horseshoe-shaped or rectangular plates made of insulating material, on the surface of which a resistive layer is applied, which has a certain ohmic resistance.
Resistors with horseshoe-shaped resistive element has a round shape and rotational movement of the slider with a rotation angle of 230 - 270°, and resistors with rectangular the resistive element has a rectangular shape and the translational movement of the slider. The most popular resistors are the types SP, OSB, SPE and SP3. The figure below shows a SP3-4 type potentiometer with a horseshoe-shaped resistive element.
The domestic industry produced potentiometers of the SPO type, in which the resistive element is pressed into an arcuate groove. The body of such a resistor is made of ceramic, and to protect against dust, moisture and mechanical damage, as well as for electrical shielding purposes, the entire resistor is covered with a metal cap.
Potentiometers of the SPO type have high wear resistance, are insensitive to overloads and are small in size, but they have a drawback - the difficulty of obtaining nonlinear functional characteristics. These resistors can still be found in old domestic radio equipment.
1.2. Wire.
IN wire In potentiometers, the resistance is created by a high-resistance wire wound in one layer on a ring-shaped frame, along the edge of which a moving contact moves. To obtain reliable contact between the brush and the winding, the contact track is cleaned, polished, or ground to a depth of 0.25d.
The structure and material of the frame is determined based on the accuracy class and the law of change in resistance of the resistor (the law of change in resistance will be discussed below). The frames are made of a plate, which, after winding the wires, is rolled into a ring, or a finished ring is taken, on which the winding is laid.
For resistors with an accuracy not exceeding 10 - 15%, the frames are made of a plate, which, after winding the wires, is rolled into a ring. The material for the frame is insulating materials such as getinax, textolite, fiberglass, or metal - aluminum, brass, etc. Such frames are easy to manufacture, but do not provide precise geometric dimensions.
Frames from the finished ring are manufactured with high precision and are mainly used for the manufacture of potentiometers. The material for them is plastic, ceramics or metal, but the disadvantage of such frames is the difficulty of winding, since special equipment is required to wind it.
The winding is made of wires made of alloys with high electrical resistivity, for example, constantan, nichrome or manganin in enamel insulation. For potentiometers, wires made of special alloys based on noble metals are used, which have reduced oxidation and high wear resistance. The diameter of the wire is determined based on the permissible current density.
2. Basic parameters of variable resistors.
The main parameters of resistors are: total (nominal) resistance, form of functional characteristics, minimum resistance, rated power, rotational noise level, wear resistance, parameters characterizing the behavior of the resistor under climatic influences, as well as dimensions, cost, etc. However, when choosing resistors, attention is most often paid to the nominal resistance and less often to the functional characteristics.
2.1. Nominal resistance.
Nominal resistance resistor is indicated on its body. According to GOST 10318-74, the preferred numbers are 1,0 ; 2,2 ; 3,3 ; 4,7 Ohm, kiloohm or megaohm.
For foreign resistors, the preferred numbers are 1,0 ; 2,0 ; 3,0 ; 5.0 Ohm, kiloohm and megaohm.
Permissible deviations of resistances from the nominal value are set within ±30%.
The total resistance of the resistor is the resistance between the outer terminals 1 and 3.
2.2. Form of functional characteristics.
Potentiometers of the same type may differ in their functional characteristics, which determine by what law the resistance of the resistor changes between the extreme and middle terminals when the resistor knob is turned. According to the form of functional characteristics, potentiometers are divided into linear And nonlinear: for linear ones, the resistance value changes in proportion to the movement of the current collector; for nonlinear ones, it changes according to a certain law.
There are three basic laws: A— Linear, B– Logarithmic, IN— Reverse Logarithmic (Exponential). So, for example, to regulate the volume in sound-reproducing equipment, it is necessary that the resistance between the middle and extreme terminals of the resistive element varies according to inverse logarithmic law (B). Only in this case is our ear able to perceive a uniform increase or decrease in volume.
Or in measuring instruments, for example, audio frequency generators, where variable resistors are used as frequency-setting elements, it is also required that their resistance varies according to logarithmic(B) or inverse logarithmic law. And if this condition is not met, then the generator scale will be uneven, which will make it difficult to accurately set the frequency.
Resistors with linear characteristic (A) are used mainly in voltage dividers as adjustment or trimmers.
The dependence of the change in resistance on the angle of rotation of the resistor handle for each law is shown in the graph below.
To obtain the desired functional characteristics, major changes are not made to the design of potentiometers. For example, in wirewound resistors, the wires are wound with varying pitches or the frame itself is made of varying width. In non-wire potentiometers, the thickness or composition of the resistive layer is changed.
Unfortunately, adjustable resistors have relatively low reliability and limited service life. Often, owners of audio equipment that has been in use for a long time hear rustling and crackling sounds from the speaker when turning the volume control. The reason for this unpleasant moment is a violation of the contact of the brush with the conductive layer of the resistive element or wear of the latter. The sliding contact is the most unreliable and vulnerable point of a variable resistor and is one of the main reasons for component failure.
3. Designation of variable resistors on diagrams.
On circuit diagrams, variable resistors are designated in the same way as constant ones, only an arrow directed to the middle of the case is added to the main symbol. The arrow indicates regulation and at the same time indicates that this is the middle output.
Sometimes situations arise when requirements for reliability and service life are imposed on a variable resistor. In this case, smooth control is replaced by step control, and a variable resistor is built on the basis of a switch with several positions. Constant resistance resistors are connected to the switch contacts, which will be included in the circuit when the switch knob is turned. And in order not to clutter the diagram with the image of a switch with a set of resistors, only the symbol of a variable resistor with a sign is indicated step regulation. And if there is a need, then the number of steps is additionally indicated.
To control volume and timbre, recording level in stereo sound-reproducing equipment, to control frequency in signal generators, etc. apply dual potentiometers, the resistance of which changes simultaneously when turning general axis (engine). In the diagrams, the symbols of the resistors included in them are placed as close to each other as possible, and the mechanical connection that ensures the simultaneous movement of the sliders is shown either with two solid lines or with one dotted line.
The belonging of resistors to one double block is indicated according to their positional designation in the electrical diagram, where R1.1 is the first resistor of the dual variable resistor R1 in the circuit, and R1.2- second. If the resistor symbols are at a great distance from each other, then the mechanical connection is indicated by segments of a dotted line.
The industry produces dual variable resistors, in which each resistor can be controlled separately, because the axis of one passes inside the tubular axis of the other. For such resistors, there is no mechanical connection that ensures simultaneous movement, therefore it is not shown on the diagrams, and membership of a dual resistor is indicated according to the positional designation in the electrical diagram.
Portable household audio equipment, such as receivers, players, etc., often use variable resistors with a built-in switch, the contacts of which are used to supply power to the device circuit. For such resistors, the switching mechanism is combined with the axis (handle) of the variable resistor and, when the handle reaches the extreme position, it affects the contacts.
As a rule, in the diagrams, the contacts of the switch are located near the power source in the break of the supply wire, and the connection between the switch and the resistor is indicated by a dotted line and a dot, which is located at one of the sides of the rectangle. This means that the contacts close when moving from a point, and open when moving towards it.
4. Trimmer resistors.
Trimmer resistors are a type of variables and are used for one-time and precise adjustment of electronic equipment during its installation, adjustment or repair. As trimmers, both variable resistors of the usual type with a linear functional characteristic, the axis of which is made “under a slot” and equipped with a locking device, and resistors of a special design with increased accuracy of setting the resistance value, are used.
For the most part, specially designed tuning resistors are made in a rectangular shape with flat or circular resistive element. Resistors with a flat resistive element ( A) have a translational movement of the contact brush, carried out by a micrometric screw. For resistors with a ring resistive element ( b) the contact brush is moved by a worm gear.
For heavy loads, open cylindrical resistor designs are used, for example, PEVR.
In circuit diagrams, tuning resistors are designated in the same way as variables, only instead of the control sign, the tuning control sign is used.
5. Inclusion of variable resistors in an electrical circuit.
In electrical circuits, variable resistors can be used as rheostat(adjustable resistor) or as potentiometer(voltage divider). If it is necessary to regulate the current in an electrical circuit, then the resistor is turned on with a rheostat; if there is voltage, then it is turned on with a potentiometer.
When the resistor is turned on rheostat the middle and one extreme output are used. However, such inclusion is not always preferable, since during the regulation process, the middle terminal may accidentally lose contact with the resistive element, which will lead to an unwanted break in the electrical circuit and, as a consequence, possible failure of the part or the electronic device as a whole.
To prevent accidental breakage of the circuit, the free terminal of the resistive element is connected to a moving contact, so that if the contact is broken, the electrical circuit always remains closed.
In practice, turning on a rheostat is used when they want to use a variable resistor as an additional or current-limiting resistance.
When the resistor is turned on potentiometer All three pins are used, which allows it to be used as a voltage divider. Let's take, for example, a variable resistor R1 with such a nominal resistance that it will extinguish almost all of the power source voltage coming to the HL1 lamp. When the resistor handle is twisted to the highest position in the diagram, the resistance of the resistor between the upper and middle terminals is minimal and the entire voltage of the power source is supplied to the lamp, and it glows at full heat.
As you move the resistor knob down, the resistance between the upper and middle terminals will increase, and the voltage on the lamp will gradually decrease, causing it to not glow at full intensity. And when the resistor reaches its maximum value, the voltage on the lamp will drop to almost zero and it will go out. It is by this principle that volume control in sound-reproducing equipment occurs.
The same voltage divider circuit can be depicted a little differently, where the variable resistor is replaced by two constant resistors R1 and R2.
Well, that’s basically all I wanted to say about variable resistance resistors. In the final part, we will consider a special type of resistors, the resistance of which changes under the influence of external electrical and non-electrical factors -.
Good luck!
Literature:
V. A. Volgov - “Parts and components of radio-electronic equipment”, 1977
V. V. Frolov - “The language of radio circuits”, 1988
M. A. Zgut - “Symbols and radio circuits”, 1964
An electrical circuit is impossible without the presence of resistance in it, which is confirmed by Ohm's law. That is why the resistor is rightfully considered the most common radio component. This state of affairs suggests that knowledge of testing such elements can always be useful when repairing electrical equipment. Let's consider the key issues related to how to check a regular resistor for serviceability using a tester or multimeter.
Main stages of testing
Despite the variety of resistors, conventional elements of this class have a linear current-voltage characteristic, which greatly simplifies the test, reducing it to three stages:
- visual inspection;
- the radio component is tested for breakage;
- Compliance with the nominal value is checked.
If everything is clear with the first and second points, then with the last there are nuances, namely, you need to find out the nominal resistance. Having a schematic diagram, this will not be difficult to do, but the trouble is that modern household appliances are rarely equipped with technical documentation. You can get out of this situation by determining the denomination from the markings. We'll briefly tell you how to do this.
Types of markings
On components produced during the Soviet Union, it was customary to indicate the denomination on the body of the part (see Fig. 1). This option did not require decoding, but if the integrity of the structure was damaged or the paint burned out, problems with text recognition could arise. In such cases, you could always turn to the circuit diagram that supplied all household appliances.
Figure 1. “ULI” resistor, the part rating and tolerance are visible on the bodyColor designation
Now color marking has been adopted, representing from three to six rings of different colors (see Fig. 2). There is no need to see this as the machinations of enemies, since this method allows you to set the denomination even on a heavily damaged part. And this is a significant factor, given that modern household electrical appliances are not equipped with circuit diagrams.
Rice. 2. Example of color marking Information on decoding this designation on components is easy to find on the Internet, so it makes no sense to present it within the framework of this article. There are also many calculator programs (including online) that allow you to obtain the necessary information.
Marking of SMD elements
Surface-mounted components (for example, SMD resistor, diode, capacitor, etc.) began to be marked with numbers, but due to the small size of the parts, this information needed to be encrypted. For resistances, in most cases, a designation of three numbers is accepted, where the first two are the value, and the last is the multiplier (see Fig. 3).
Rice. 3. An example of decoding the value of an SMD resistor Visual inspection
Violation of the normal operating mode causes overheating of the part, therefore, in most cases, the problematic element can be identified by its appearance. This can be either a change in the color of the case or its complete or partial destruction. In such cases, it is necessary to replace the burnt element.
Figure 4. A clear example of how a resistor can burn out Notice in the photo above, the component marked "1" clearly needs to be replaced, while the adjacent parts "2" and "3" may be working, but need to be checked.
Checking for a break
Actions are performed in the following order:
If the model of the device you are using differs from the one shown in the figure, read the instructions that came with the multimeter.
- We touch the pins of the problematic element on the board with the probes. If the part “does not ring” (the multimeter will show the number 1, that is, an infinitely large resistance), we can state that the test showed a break in the resistor.
Please note that this testing can be carried out without desoldering the element from the board, but this does not guarantee a 100% result, since the tester can show communication through other components of the circuit.
Validation check
If the part is soldered, then this stage will guarantee its functionality. For testing we need to know the denomination. How to identify it by markings was written above.
The algorithm of our actions is as follows:
What is clearance and how important is it?
This value shows the possible deviation of a given series from the specified nominal value. A correctly calculated circuit must take this indicator into account, or appropriate adjustments are made after assembly. As you understand, our friends from the Celestial Empire do not bother themselves with this, which has a positive effect on the cost of their goods.
The result of such a policy was shown in Figure 4; the part works for some time until the limit of its safety margin is reached.
- We make a decision by comparing the readings of the multimeter with the nominal value; if the discrepancy goes beyond the error limits, the part definitely needs to be replaced.
How to test a variable resistor?
The principle of operation in this case is not very different; we will describe them using the example of the part shown in Figure 7.
Rice. 7. Trimmer resistor (internal circuit marked with red circle) The algorithm is as follows:
- We take a measurement between legs “1” and “3” (see Fig. 7) and compare the resulting value with the nominal value.
- We connect the probes to terminals “2” and any of the remaining ones (“1” or “3”, it doesn’t matter).
- We rotate the adjustment knob and observe the readings of the device; they should change in the range from 0 to the value obtained in step 1.
How to check a resistor with a multimeter without desoldering on the board?
This testing option is only permissible with low-resistance elements. Above 80-100 ohms, it is likely that other components will interfere with the measurement. The final answer can only be given by carefully studying the circuit diagram.
Often, during an external inspection, damage to the varnish or enamel coating can be detected. A resistor with a charred surface or with rings on it is also faulty. A slight darkening of the varnish coating is acceptable for such resistors; the resistance value should be checked. The permissible deviation from the nominal value should not exceed ±20%. An increasing deviation of the resistance value from the nominal value is observed during long-term operation of high-resistance resistors (more than 1 MOhm).
In some cases, a break in the conductive element does not cause any changes in the appearance of the resistor. Therefore, resistors are checked to ensure that their values correspond to the nominal values using an ohmmeter. Before measuring the resistance of resistors in the circuit, turn off the receiver and discharge the electrolytic capacitors. When measuring, it is necessary to ensure reliable contact between the terminals of the resistor being tested and the terminals of the device. To avoid shunting the device, do not touch the metal parts of the ohmmeter probes with your hands. The value of the measured resistance must correspond to the value indicated on the resistor body, taking into account the tolerance corresponding to the class of this resistor and the inherent error of the measuring device. For example, when measuring the resistance of a Class I accuracy resistor using the Ts-4324 device, the total error during measurement can reach ±15% (resistor tolerance ±5% plus instrument error ±10). If the resistor is checked without. If you remove it from the circuit, it is necessary to take into account the influence of shunt circuits.
The most common fault with resistors is burnout of the conductive layer, which can be caused by the passage of an unacceptably large current through the resistor as a result of various short circuits in the installation or breakdown of the capacitor. Wirewound resistors are much less likely to fail. Their main faults (wire breakage or burnout) are usually found using an ohmmeter.
Variable resistors (potentiometers) most often have poor contact between the moving brush and the conductive elements of the resistor. If such a potentiometer is used in a radio receiver to adjust the volume, then when its axis is rotated, crackling sounds are heard in the head of the dynamic loudspeaker. There are also breaks, wear or damage to the conductive layer.
The serviceability of potentiometers is determined with an ohmmeter. To do this, connect one of the ohmmeter probes to the middle lobe of the potentiometer, and the second probe to one of the outer petals. With each such connection, the regulator axis is rotated very slowly. If the potentiometer is working properly, then the ohmmeter needle moves along the scale smoothly, without shaking or jerking. Trembling and jerking of the needle indicates poor contact of the brush with the conductive element. If the ohmmeter needle does not deflect at all, this means that the resistor is faulty. It is recommended to repeat this test by switching the second ohmmeter probe to the second outermost lobe of the resistor to make sure that this pin is also working properly. A faulty potentiometer must be replaced with a new one or repaired if possible. To do this, open the potentiometer housing and thoroughly wash the conductive element with alcohol and apply a thin layer of machine oil. Then it is reassembled and the reliability of the contact is checked again.
Resistors found to be unsuitable are usually replaced with serviceable ones, the values of which are selected so that they correspond to the circuit diagram of the receiver. If there is no resistor with the appropriate resistance, it can be replaced by two (or several) parallel or series connected. When connecting two resistors in parallel, the total resistance of the circuit can be calculated using the formula
where P is the power dissipated by the resistor, W; U is the voltage across the resistor. IN; R - resistor resistance value; Ohm.
It is advisable to take a resistor with a slightly higher dissipation power (30,..40%) than that obtained in the calculation. If you do not have a resistor of the required power, you can select several smaller resistors. power and connect them together in parallel or in series so that their total resistance is equal to the one being replaced, and the total power is not lower than the required one.
When determining the interchangeability of various types of fixed and variable resistors for the latter, the characteristics of the change in resistance depending on the angle of rotation of its axis are also taken into account. The choice of the potentiometer change characteristic is determined by its circuit purpose. For example, in order to obtain uniform control of the volume of a radio receiver, you should choose potentiometers of group B (with an exponential dependence of the change in resistance), and in the tone control circuits - group A.
When replacing failed resistors of the BC type, we can recommend resistors of the MLT type with the appropriate dissipation power, having smaller dimensions and better moisture resistance. The rated power of the resistor and its accuracy class are not significant in the control grid circuits of lamps and collectors of low-power transistors.
When assembling any device, even the simplest one, radio amateurs often have problems with radio components; it happens that they cannot get some kind of resistor of a certain value, a capacitor or a transistor... in this article I want to talk about replacing radio components in circuits, which radio elements can be replaced with what and which ones are not allowed, how they differ, what types of elements are used in which nodes, and much more. Most radio components can be replaced with similar ones with similar parameters.
Let's start with resistors.
So, you probably already know that resistors are the most basic elements of any circuit. Without them, no circuit can be built, but what to do if you do not have the necessary resistances for your circuit? Let's look at a specific example, take for example the LED flasher circuit, here it is in front of you:
In order to understand which resistors here can be changed within what limits, we need to understand what they generally affect. Let's start with resistors R2 and R3 - they influence (together with capacitors) the blinking frequency of the LEDs, i.e. You can guess that by changing the resistance up or down, we will change the blinking frequency of the LEDs. Therefore, these resistors in this circuit can be replaced with similar ones in value if you do not have those indicated on the circuit. To be more precise, in this circuit you can use resistors, say, from 10 kOhm to 50 kOhm. As for resistors R1 and R4, to some extent the operating frequency of the generator also depends on them; in this circuit they can be set from 250 to 470 Ohms. There is one more point here, LEDs come in different voltages, if this circuit uses LEDs with a voltage of 1.5 volts, and we put an LED with a higher voltage there - they will burn very dimly, therefore, we need resistors R1 and R4 will put on less resistance. As you can see, the resistors in this circuit can be replaced with other, similar values. Generally speaking, this applies not only to this circuit, but also to many others; if, say, when assembling the circuit, you did not have a 100 kOhm resistor, you can replace it with 90 or 110 kOhm, the smaller the difference, the better it is not to use 10 kOhm instead of 100 kOhm , otherwise the circuit will not work correctly or even some element may fail. By the way, do not forget that resistors have a permissible nominal deviation. Before changing the resistor to another, carefully read the description and operating principle of the circuit. In precision measuring instruments, you should not deviate from the nominal values specified in the diagram.
Now, as for the power, the more powerful the resistor, the thicker it is, there is no way to install a 0.125 watt resistor instead of a powerful 5 watt one; at best it will get very hot, at worst it will simply burn out.
And you are always welcome to replace a low-power resistor with a more powerful one, nothing will come of it, only powerful resistors are larger, you will need more space on the board, or you will have to place it vertically.
Do not forget about parallel and series connection of resistors, if you need a 30 kOhm resistor, you can make it from two 15 kOhm resistors, connected in series.
In the circuit that I gave above, there is a trimming resistor. Of course, it can be replaced with a variable, there is no difference, the only thing is that the trimmer will have to be turned with a screwdriver. Is it possible to change trimmer and variable resistors in circuits to ones that are close in value? In general, yes, in our circuit it can be set to almost any value, at least 10 kOhm, at least 100 kOhm - the regulation limits will simply change, if we set it to 10 kOhm, by rotating it we will quickly change the blinking frequency of the LEDs, and if we set it to 100 kOhm, the blinking frequency will be adjusted produced more smoothly and “longer” than with 10k. In other words, at 100 kOhm the adjustment range will be wider than at 10 kOhm.
But replacing variable resistors with cheaper trimmers is not worth it. Their motor is rougher and with frequent use the conductive layer is severely scratched, after which, when the motor rotates, the resistance of the resistor can change abruptly. An example of this is wheezing in the speakers when changing the volume.
You can read more about the types and types of resistors.
Now let's talk about capacitors, they come in different types, types and, of course, capacities. All capacitors differ in such basic parameters as rated capacity, operating voltage and tolerance. There are two types of capacitors used in radio electronics: polar and non-polar. The difference between polar capacitors and non-polar ones is that polar capacitors must be included in the circuit while strictly observing the polarity. Capacitors are shaped like radial, axial (the terminals of such capacitors are on the side), with threaded terminals (usually high-capacity or high-voltage capacitors), flat, and so on. There are pulse capacitors, noise suppression capacitors, power capacitors, audio capacitors, general capacitors, etc.
Where are which capacitors used?
In the filters of power supplies, ordinary electrolytic ones are used, sometimes ceramics are also used (they serve to filter and smooth the rectified voltage), high-frequency electrolytes are used in the filters of switching power supplies, ceramics are used in power circuits, and ceramics are also used in non-critical circuits.
On a note!
Electrolytic capacitors usually have a high leakage current, and the capacitance error can be 30-40%, i.e. The capacity indicated on the can may vary greatly in reality. The nominal capacity of such capacitors decreases as they age. The most common defect of old electrolytic capacitors is loss of capacity and increased leakage; such capacitors should not be used further.
Let's return to our multivibrator (flasher) circuit, as you can see there are two electrolytic polar capacitors, they also affect the blinking frequency of the LEDs, the larger the capacitance, the slower they will blink, the smaller the capacitance, the faster they will blink.
In many devices and instruments, you cannot “play” with capacitor capacities in this way, for example, if the circuit has 470 μF, then you should try to put 470 μF, or 2 220 μF capacitors in parallel. But again, it depends on which node the capacitor is located in and what role it plays.
Let's look at an example using a low frequency amplifier:
As you can see, there are three capacitors in the circuit, two of which are non-polar. Let's start with capacitors C1 and C2, they are at the input of the amplifier, a sound source passes/is supplied through these capacitors. What will happen if instead of 0.22 µF we put 0.01 µF? Firstly, the sound quality will deteriorate slightly, and secondly, the sound in the speakers will become noticeably quieter. And if instead of 0.22 µF we set 1 µF, then at high volumes we will experience wheezing in the speakers, the amplifier will overload, it will heat up more, and the sound quality may deteriorate again. If you look at the circuit diagram of some other amplifier, you may notice that the input capacitor can be 1 µF or even 10 µF. It all depends on each specific case. But in our case, 0.22 µF capacitors can be replaced with similar ones, for example 0.15 µF or better 0.33 µF.
So, we have reached the third capacitor, it is polar, it has a plus and a minus, you cannot confuse the polarity when connecting such capacitors, otherwise they will heat up, or, even worse, explode. And they bang very, very loudly, it can cause your ears to become blocked. We have a capacitor C3 with a capacity of 470 uF in the power circuit; if you don’t know yet, then I will say that in such circuits, and for example in power supplies, the larger the capacitance, the better.
Nowadays every home has computer speakers, maybe you have noticed that if you listen to music loudly, the speakers wheeze, and the LED in the speaker blinks. This usually just means that the capacitor capacity in the power supply filter circuit is small (+ the transformers are weak, but I won’t talk about that). Now let's return to our amplifier, if instead of 470 uF we put 10 uF - this is almost the same as not installing a capacitor at all. As I already said, in such circuits, the larger the capacitance, the better; to be honest, in this circuit, 470 μF is very little, you can put all 2000 μF.
It is impossible to put a capacitor at a lower voltage than it is in the circuit, this will cause it to heat up and explode; if the circuit operates from 12 volts, then you need to install the capacitor at 16 volts; if the circuit operates from 15-16 volts, then it is better to place the capacitor at 25 volts.
What to do if the circuit you are assembling contains a non-polar capacitor? A non-polar capacitor can be replaced with two polar ones by connecting them in series in the circuit, the pluses are connected together, and the capacitance of the capacitors should be twice as large as indicated on the circuit.
Never discharge capacitors by shorting their terminals! You should always discharge through a high-resistance resistor, but do not touch the terminals of the capacitor, especially if it is high-voltage.
Almost all polar electrolytic capacitors have a cross pressed into them on the top; this is a kind of protective notch (often called a valve). If alternating voltage is applied to such a capacitor or the permissible voltage is exceeded, the capacitor will begin to get very hot, and the liquid electrolyte inside it will begin to expand, after which the capacitor will burst. This often prevents the capacitor from exploding, causing the electrolyte to leak out.
In this regard, I would like to give a little advice: if after repairing any equipment, after replacing capacitors, you turn it on for the first time (for example, in old amplifiers all electrolytic capacitors are replaced), close the lid and keep your distance, God forbid that something goes wrong.
Now the final question: is it possible to connect a 230-volt non-polar capacitor to a 220-volt network? And at 240? Just please, don’t immediately grab such a capacitor and plug it into a socket!
For diodes, the main parameters are the permissible forward current, reverse voltage and forward voltage drop; sometimes you also need to pay attention to the reverse current. Such parameters of replacement diodes must be no less than those of the ones being replaced.
Low-power germanium diodes have a much higher reverse current than silicon diodes. The forward voltage drop of most germanium diodes is approximately half that of similar silicon diodes. Therefore, in circuits where this voltage is used to stabilize the operating mode of the circuit, for example in some final audio amplifiers, replacing diodes with a different type of conductivity is not permissible.
For rectifiers in power supplies, the main parameters are reverse voltage and maximum permissible current. For example, for currents of 10A you can use diodes D242...D247 and similar ones; for a current of 1 ampere you can use KD202, KD213; among imported ones, these are diodes of the 1N4xxx series. Of course, you can’t install a 1-amp diode instead of a 5-amp diode; on the contrary, it’s possible.
In some circuits, for example, in switching power supplies, Schottky diodes are often used; they operate at higher frequencies than conventional diodes; these should not be replaced with conventional diodes, they will quickly fail.
In many simple circuits, any other diode can be used as a replacement; the only thing is, don’t confuse the output; you should treat this with caution, because diodes can also burst or smoke (in the same power supplies) if the anode is confused with the cathode.
Is it possible to connect diodes (including Schottky diodes) in parallel? Yes, it is possible, if two diodes are connected in parallel, the current flowing through them can be increased, the resistance, voltage drop across the open diode and power dissipation are reduced, therefore, the diodes will heat up less. Diodes can only be paralleled with the same parameters, from the same box or batch. For low-power diodes, I recommend installing a so-called “current equalizing” resistor.
Transistors are divided into low-power, medium-power, high-power, low-frequency, high-frequency, etc. When replacing, you need to take into account the maximum permissible emitter-collector voltage, collector current, power dissipation, and, of course, the gain.
The replacement transistor, firstly, must belong to the same group as the one being replaced. For example, low low frequency power or high medium frequency power. Then a transistor of the same structure is selected: p-p-p or p-p-p, a field-effect transistor with a p-channel or n-channel. Next, the values of the limiting parameters are checked; the replacement transistor must have them no less than the one being replaced.
It is recommended to replace silicon transistors only with silicon ones, germanium ones with germanium ones, bipolar ones with bipolar ones, etc.
Let's return to the circuit of our flasher, it uses two n-p-n structure transistors, namely KT315, these transistors can easily be replaced with KT3102, or even with an old MP37, suddenly someone has a lot of transistors lying around that can work in this circuit.
Do you think KT361 transistors will work in this circuit? Of course not, KT361 transistors have a different structure, p-n-p. By the way, an analogue of the KT361 transistor is KT3107.
In devices where transistors are used in key modes, for example, in control stages of relays, LEDs, in logic circuits, etc... the choice of transistor does not matter much, choose a similar power and similar parameters.
In some circuits, for example, KT814, KT816, KT818 or KT837 can be replaced with each other. Let's take a transistor amplifier as an example, its diagram is below.
The output stage is built on KT837 transistors, they can be replaced with KT818, but the KT816 is no longer worth replacing, it will get very hot and will quickly fail. In addition, the amplifier's output power will decrease. Transistor KT315, as you probably already guessed, changes to KT3102, and KT361 to KT3107.
A high-power transistor can be replaced by two low-power transistors of the same type; they are connected in parallel. When connected in parallel, transistors should be used with similar gain values; it is recommended to install equalizing resistors in the emitter circuit of each, depending on the current: from tenths of an ohm at high currents, to units of ohms at low currents and powers. In field-effect transistors, such resistors are usually not installed, because they have a positive TKS channel.
I think we’ll finish here, in conclusion I want to say that you can always ask Google for help, it will always tell you, give you tables for replacing radio components with analogues. Good luck!
