The following no less common parts, widely used in pocket receivers, are permanent capacitors a wide variety of capacities. In high-frequency circuits where low capacitance is required, it is advisable to use special miniature capacitors such as KDM and KTM, produced by industry with nominal values from 1 to 1500 pF and from 1 to 3000 pF, respectively. These capacitors are relatively scarce, but there is a replacement for them, namely: widespread capacitors of the KTK-1 type with nominal values from 2 to 180 pF, KSO-1 from 21 to 750 pF and KSO-2 from 100 to 2400 pF. The latter type of capacitors are somewhat larger in size than the first two, but they can be “miniaturized.” The protective plastic molding must be removed from the capacitor and replaced with impregnation with nitro varnish or BF-2 glue. This way it is possible to obtain a very miniature part.
As isolation and blocking capacitors in high-frequency circuits of receivers, capacitors of significantly larger capacitance than indicated above are used. Capacitors of the KDS type with a capacity of 1000, 3000 and 6800 pF, KLS and KM with a capacity of 0.01, 0.033 and 0.047 μF, well known to radio amateurs, are suitable here. True, the last two types of capacitors are relatively scarce, but they can be successfully replaced with capacitors of somewhat larger dimensions, for example, the MBM type for 160 V.
When selecting capacitors of the required capacity, one should not forget about the possibility of connecting them in series and in parallel. Regarding tolerance, the following must be taken into account. The nominal values of capacitors used in high-frequency circuits must be close to the recommended ones and within a tolerance of ±5-10%. Capacitors used for blocking can have a tolerance of up to ±20%. There is no need to talk about the operating voltage of the types of capacitors discussed above, since it is many times higher than what will be applied to them in transistor receiver circuits. |
In addition to capacitors of relatively small capacity, in transistor circuits Separation and blocking capacitors with a capacity of 0.5 to 100.0 μF, and sometimes more, are used. Common types of high-capacity capacitors are domestic miniature electrolytic capacitors of the EM and EM-M types, produced by industry with nominal values from 0.5 to 50.0 μF, which can be replaced with Tesla capacitors, which are periodically supplied to our radio stores.
When installing electrolytic capacitors in a circuit, in order to avoid possible failure, it is necessary to strictly observe the indicated polarity of connection. Determine the polarity of the capacitors. high-quality production is easy by the corresponding inscription (+) made on the case on the side of the output, isolated from it and connected to the plate connected to the plus of the power source; the opposite terminal, connected to the capacitor body, must be connected to the minus (Fig. 1, /). For capacitors manufactured by Tesla, the terminal isolated from the housing is positive (Fig. 1, 2).
In addition to the switching polarity, the operating voltage of the electrolytic capacitors should also be taken into account, which in no case should be less than that recommended in the description of a particular receiver and, as a rule, indicated on schematic diagram together with the nominal value of the capacitance.
The capacitance of the isolation capacitors can have a tolerance of up to +50%, and of the blocking capacitors up to +100-500%, which in some cases will only contribute to more stable operation of the circuit.
In addition to constant capacitors, almost all pocket receiver circuits contain variable capacitors: single ones in direct amplification receivers and combined into dual blocks in superheterodyne type receivers. Of the ready-made single capacitors, a ceramic tuning capacitor of the KPK-2 type with a capacity of 25-150 pf has become widespread. Besides him, in pro-
Fig. 1 External lead of common parts and pin locations: J – EM type capacitors. EM M, 2– b “dei! sators of the Tesla company, 3 ¦ tra.pistors type P13, GSh. P15. P16, P8. P9. PYU PI; – transistors type "pi m P40E P403A-5 circuit for determining the reverse current of the collector; (5 – diagram for determining
for transistor gain ¦ 7 – diodes of the D2 series; 8 – diodes of the D1 and D9 series; “low-frequency transformer /v – circuit diagram of the windings of the matching transformer: P – circuit diagram of the output transformer windings; 12 – capsule type DEMSH-1a: 13 – diagram of the windings of the capsule type DEMSH-1a.
There are even special single miniature capacitors with a solid dielectric, produced by our industry with a minimum capacity of 5 pf and a maximum of 350 pf, as well as Tesla capacitors with similar parameters.
Of the ready-made dual condenser blocks, you can use those used in portable receivers, for example, “Neva”, “Neva-2”, “Gauja”, “Selga”, “Start”, “Topaz”, “Sokol”, etc. Their maximum The capacitance ranges from 180 to 240 pf. In addition to them, a dual block of Tesla variable capacitors with a maximum capacity of 360-380 pF is also available for sale. The industrial tolerance for capacitance of the listed capacitors does not exceed ±10%. When selecting the required tuning capacitor, a novice radio amateur must adhere to the recommendations given in the description of a particular circuit he is assembling. A significant deviation of the capacitor capacitance from the required value, exceeding ±10%, will require recalculation of the winding data of the high-frequency coils of the oscillating circuits. Otherwise, the circuit settings will change and the receiver may become unusable. This remark is especially true for superheterodynes.
In cases where the maximum capacitance of the capacitor is significantly greater than the recommended value, recalculation of the loop coil data can be avoided if an additional mating capacitor is introduced into the circuit, connected in series with the main one. The capacitance of the mating capacitor is selected so that the total maximum capacitance is equal to that recommended in the description.
In direct amplification receivers, you can avoid recalculating the loop coil data when using a tuning capacitor with a smaller capacitance than required, but you should remember that the operating range of the receiver will change.
A few words should be said about trimmer capacitors with a small maximum capacity. They are typically used to precisely couple the input and local oscillator circuits of superheterodyne receivers. Most industrial dual units have their own tuning capacitors KPE built into the housing. If they are not available, then you can use standard KPKM type trimmers with a maximum capacity of 15-30 pF or any others that are suitable in size.
Starting and running capacitors are used to start and operate electric motors operating in a single-phase 220 V network.
That's why they are also called phase shifters.
Installation location - between the power line and the starting winding of the electric motor.
Symbol for capacitors in diagrams
The graphic designation on the diagram is shown in the figure, the letter designation is C and the serial number according to the diagram.
Basic parameters of capacitors
Capacitor capacity- characterizes the energy that a capacitor is capable of accumulating, as well as the current that it is capable of passing through itself. Measured in Farads with a multiplying prefix (nano, micro, etc.).
The most commonly used values for run and start capacitors range from 1 μF to 100 μF.
Nominal voltage of the capacitor - voltage at which the capacitor is able to operate reliably and for a long time, maintaining its parameters.
Well-known capacitor manufacturers indicate on its body the voltage and the corresponding guaranteed operating time in hours, for example:
- 400 V - 10000 hours
- 450 V - 5000 hours
- 500 V - 1000 hours
Checking the starting and running capacitors
You can check the capacitor using a capacitor capacitance meter; such devices are produced both separately and as part of a multimeter, a universal device that can measure many parameters. Let's consider checking with a multimeter.
- de-energize the air conditioner
- discharge the capacitor by short-circuiting its terminals
- remove one of the terminals (any)
- We set the device to measure the capacitance of capacitors
- We lean the probes against the terminals of the capacitor
- read the capacity value from the screen
All devices have different designations for the capacitor measurement mode; the main types are shown below in the pictures.
In this multimeter, the mode is selected by a switch; it must be set to Fcx mode. The probes must be inserted into the sockets marked Cx.
Switching the capacitance measurement limit is manual. Maximum value 100 µF.
This one has measuring instrument automatic mode, you just need to select it, as shown in the picture.
The Mastech measuring tweezers also automatically measure capacitance, you just need to select the mode with the FUNC button, pressing it until the F indication appears.
To check the capacitance, we read its value on the capacitor body and set a deliberately larger measurement limit on the device. (If it's not automatic)
For example, the nominal value is 2.5 μF (μF), on the device we set 20 μF (μF).
After connecting the probes to the terminals of the capacitor, we wait for the readings on the screen, for example, the time to measure a capacitance of 40 μF with the first device is less than one second, with the second one more than one minute, so you should wait.
If the rating does not correspond to that indicated on the capacitor body, then it must be replaced and, if necessary, an analogue must be selected.
Replacement and selection of starting/running capacitor
If you have an original capacitor, then it is clear that you simply need to put it in place of the old one and that’s it. Polarity does not matter, that is, the terminals of the capacitor do not have the designations plus “+” and minus “-” and they can be connected in any way.
It is strictly forbidden to use electrolytic capacitors (you can recognize them by their smaller sizes, with the same capacity, and the plus and minus markings on the case). As a consequence of application - thermal destruction. For these purposes, manufacturers specially produce non-polar capacitors for operation in the circuit alternating current, which have convenient fastening and flat terminals for quick installation.
If the required denomination is not available, you can obtain it parallel connection capacitors. The total capacitance will be equal to the sum of the two capacitors:
C total = C 1 + C 2 +...C p
That is, if we connect two 35 μF capacitors, we get a total capacity of 70 μF, the voltage at which they can operate will correspond to their rated voltage.
Such a replacement is absolutely equivalent to one capacitor of larger capacity.
Types of capacitors
To start powerful compressor engines, oil-filled non-polar capacitors are used.
The housing is filled with oil inside for good heat transfer to the surface of the housing. The body is usually metal or aluminum.
The most affordable capacitors of this type CBB65.
To start less powerful loads, such as fan motors, dry capacitors are used, the housing of which is usually plastic.
The most common capacitors of this type CBB60, CBB61.
The terminals are double or quadruple for ease of connection.
In the element base of a computer (and not only) there is one bottleneck - electrolytic capacitors. They contain an electrolyte, the electrolyte is a liquid. Therefore, heating such a capacitor leads to its failure, as the electrolyte evaporates. And heating in the system unit is a regular occurrence.
Therefore, replacing capacitors is a matter of time. More than half of the failures of motherboards in the middle and lower price categories are due to dry or swollen capacitors. They break even more often for this reason. computer blocks nutrition.
Since the printing on modern boards is very dense, replacing capacitors must be done very carefully. You can damage and not notice a small unframed element or break (short) tracks, the thickness and distance between which is slightly greater than the thickness of a human hair. It’s quite difficult to fix something like this later. So be careful.
So, to replace capacitors you will need a soldering iron with a thin tip with a power of 25-30 W, a piece of thick guitar string or a thick needle, soldering flux or rosin.
If you reverse the polarity when replacing an electrolytic capacitor or install a capacitor with a low voltage rating, it may well explode. And here's what it looks like:
So, carefully select the replacement part and install it correctly. Electrolytic capacitors are always marked with a negative terminal (usually a vertical stripe of a different color from the body color). On printed circuit board The hole for the negative contact is also marked (usually with black shading or solid white). The ratings are written on the capacitor body. There are several of them: voltage, capacity, tolerances and temperature.
The first two are always present, the others may be absent. Voltage: 16V(16 volts). Capacity: 220µF(220 microfarads). These values are very important when replacing. The voltage can be chosen equal or with a higher nominal value. But the capacitance affects the charging/discharging time of the capacitor and in some cases can be important for a section of the circuit.
Therefore, the capacity should be selected equal to that indicated on the case. On the left in the photo below is a green swollen (or leaking) capacitor. In general, there are constant problems with these green capacitors. The most common candidates for replacement. On the right is a working capacitor, which we will solder.
The capacitor is soldered as follows: first find the legs of the capacitor on the back side of the board (for me this is the most difficult moment). Then heat one of the legs and lightly press the capacitor body from the side of the heated leg. When the solder melts, the capacitor tilts. Carry out a similar procedure with the second leg. Usually the capacitor is removed in two steps.
There is no need to rush, and there is no need to press too hard. The motherboard is not a double-sided PCB, but a multilayer one (imagine a wafer). Overdoing it can damage the contacts on the inner layers of the printed circuit board. So no fanaticism. By the way, long-term heating can also damage the board, for example, lead to peeling or tearing of the contact pad. Therefore, there is no need to press hard with a soldering iron either. We lean the soldering iron and press lightly on the capacitor.
After removing the damaged capacitor, it is necessary to make holes so that the new capacitor can be inserted freely or with little effort. For these purposes, I use a guitar string of the same thickness as the legs of the part being soldered. A sewing needle is also suitable for these purposes, but needles are now made of ordinary iron, and strings are made of steel. There is a chance that the needle will get caught in the solder and break when you try to pull it out. And the string is quite flexible and steel and solder adhere much worse than iron.
When removing capacitors, solder most often clogs the holes in the board. If you try to solder the capacitor in the same way that I advised you to solder it, you can damage the contact pad and the track leading to it. Not the end of the world, but a very undesirable occurrence. Therefore, if the holes are not clogged with solder, they simply need to be expanded. And if you do, then you need to press the end of the string or needle tightly to the hole, and on the other side of the board, lean the soldering iron against this hole. If this option is inconvenient, then the soldering iron tip should be leaned against the string almost at the base. When the solder melts, the string will fit into the hole. At this moment you need to rotate it so that it does not grab the solder.
After obtaining and expanding the hole, it is necessary to remove excess solder from its edges, if any, otherwise, during soldering of the capacitor, a tin cap may form, which can solder adjacent tracks in those places where the seal is dense. Pay attention to the photo below - how close the tracks are to the holes. Soldering this is very easy, but difficult to notice, since the installed capacitor interferes with the view. Therefore, it is very advisable to remove excess solder.
If you don’t have a radio market nearby, then most likely you can only find a used capacitor for replacement. Before installation, its legs should be treated, if necessary. It is advisable to remove all solder from the legs. I usually coat the legs with flux and tin the soldering iron tip with a clean soldering iron tip, the solder collects on the soldering iron tip. Then I scrape the legs of the capacitor with a utility knife (just in case).
That's all, actually. We insert the capacitor, lubricate the legs with flux and solder. By the way, if you use pine rosin, it is better to crush it into powder and apply it to the installation site than to dip a soldering iron in a piece of rosin. Then it will work out neatly.
Replacing a capacitor without desoldering it from the board
Repair conditions vary, and changing a capacitor on a multilayer (PC motherboard, for example) printed circuit board is not the same as changing a capacitor in a power supply (single-layer, single-sided printed circuit board). You must be extremely careful and careful. Unfortunately, not everyone was born with a soldering iron in their hands, and repairing (or trying to repair) something is very necessary.
As I already wrote in the first half of the article, most often the cause of breakdowns is capacitors. Therefore, replacing capacitors is the most common type of repair, at least in my case. Specialized workshops have special equipment for these purposes. If you don’t have it, you have to use ordinary equipment (flux, solder and soldering iron). In this case, experience helps a lot.
The main advantage of this method is that contact pads The boards will have to be subjected to much less heat. At least twice. Printing on cheap motherboards quite often peels off due to heat. The tracks come off, and fixing this later is quite problematic.
The disadvantage of this method is that you still have to put pressure on the board, which can also lead to negative consequences. Although from my personal experience I have never had to put too much pressure. In this case, there is every chance of soldering to the legs remaining after mechanical removal of the capacitor.
So, replacing a capacitor begins with removing the damaged part from the motherboard.
You need to place your finger on the capacitor and, with light pressure, try to swing it up and down and left and right. If the capacitor swings left and right, then the legs are located along the vertical axis (as in the photo), otherwise along the horizontal axis. You can also determine the position of the legs by the negative marker (a strip on the capacitor body indicating the negative contact).
Next, you should press the capacitor along the axis of its legs, but not sharply, but smoothly, slowly increasing the load. As a result, the leg is separated from the body, then we repeat the procedure for the second leg (press from the opposite side).
Sometimes the leg is pulled out along with the capacitor due to bad solder. In this case, you can slightly widen the resulting hole (I do this with a piece of guitar string) and insert a piece of copper wire, preferably the same thickness as the leg.
Half the job is done, now we move directly to replacing the capacitor. It is worth noting that the solder does not stick well to the part of the leg that was inside the capacitor body and it is better to bite it off with wire cutters, leaving a small part. Then the legs of the capacitor prepared for replacement and the legs of the old capacitor are treated with solder and soldered. It is most convenient to solder the capacitor by placing it on the board at an angle of 45 degrees. Then you can easily stand him at attention.
The resulting appearance is, of course, unaesthetic, but it works and this method is much simpler and safer than the previous one in terms of heating the board with a soldering iron. Happy renovation!
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Having decided to replace a capacitor on a printed circuit board, the first step is to select a replacement capacitor. As a rule, we are talking about electrolytic capacitor, which, due to the exhaustion of its working resource, began to create an abnormal mode for your electronic device, or the capacitor burst due to overheating, or maybe you just decided to install a newer or better one.
Selecting a suitable replacement capacitor
The parameters of the replacement capacitor must certainly be suitable: it Rated voltage in no case should it be lower than that of the capacitor being replaced, and the capacitance should not be lower, or may be 5-10 percent higher (if this is permissible in accordance with the circuit of this device known to you) than it was originally.
Finally, make sure the new capacitor will fit into the space that its predecessor will leave. If it turns out to be a little smaller in diameter and height, it’s not a big deal, but if the diameter or height is larger, components located nearby on the same board may interfere or it will rest against the elements of the case. It is important to take these nuances into account. So, the replacement capacitor has been selected, it suits you, now you can start dismantling the old capacitor.
Getting ready for the process
Now it will be necessary to remove the faulty capacitor from the board and prepare a place for installing a new one here. To do this, you will need, of course, and it is also convenient for this action to prepare a piece of copper braid for removing solder. As a rule, a soldering iron power within 40 W will be quite sufficient even if refractory solder was initially used on the board.
As for copper braiding to remove solder, if you don’t have one, it’s very easy to make it yourself: take a piece of not very thick copper wire, consisting of thin copper veins, remove the insulation from it, lightly (you can use simple pine rosin) - now these flux-impregnated veins will easily, like a sponge, absorb the solder from the legs of the soldered capacitor.
Soldering the old capacitor
First, look at the polarity of the soldered capacitor on the board: which way is it facing minus, so that when you solder a new one, you will not make a mistake with the polarity. Usually the negative leg is marked with a stripe. So, when the braid for desoldering is prepared, and the soldering iron is already warm enough, first lean the braid against the base of the capacitor legs that you decided to free from solder first.
Carefully melt the solder on the leg directly through the braid so that the braid also heats up and quickly draws the solder from the board. If there is too much solder on the leg, move the braid as it fills with solder, collecting all the solder from the leg onto it so that the leg ends up free of solder. Do the same with the second leg of the capacitor. Now the capacitor can be easily pulled out by hand or tweezers.
Soldering in a new capacitor
The new capacitor must be installed in compliance with the polarity, that is, the negative leg is in the same place where the negative leg of the soldered one was. Usually the minus leg is indicated by a stripe, and the plus leg is longer than the minus leg. Treat the capacitor legs with flux.
Insert the capacitor into the holes. There is no need to shorten the legs in advance. Bend the legs slightly in different directions so that the capacitor stays in place well and does not fall out.
Now, warming up the leg near the board itself with the tip of the soldering iron tip, poke the solder towards the leg so that the leg is enveloped, moistened, and surrounded by solder. Do the same with the second leg. When the solder has cooled, all you have to do is shorten the legs of the capacitor with wire cutters (to the same length as the adjacent parts on your board).
