Power adapter do-it-yourself repair

Network power adapters - miniature power supplies for various electronic household equipment. They are used to power antenna amplifiers, radiotelephones, chargers. Despite the active introduction of switching power supplies, transformer ones are still actively used and are used in the user's life.

It is not uncommon for these transformer units to fail.

If the adapter breaks down, you can replace it with a new one, their cost is low. But why give away hard-earned money if in most cases you can fix the problem yourself within 15-30 minutes and save yourself from looking for a replacement and spending money?

An adapter for 12V and a current of 0.1A from the antenna amplifier got on the repair table.

The photo shows the adapter after the repair.

What parts does a conventional transformer adapter consist of?

If you disassemble the power adapter, then inside we will find a transformer (1) and a small electronic circuit (2).

transformer (1) is used to lower the alternating mains voltage 220V to the level of 13–15 V.

The electronic circuit is used to rectify the alternating voltage (turning it into a constant voltage) and stabilize it at the level of 12V.

As you can see, the classic transformer-based power supply is quite simple. What can break in such a simple device?

Let's take a look at the concept.

On a circuit diagram T1 This is a step down transformer. Typical transformer failures are burnout or breakage of the primary wire (Ⅰ), and, more rarely, secondary (Ⅱ) windings. As a rule, the primary, network winding is faulty (Ⅰ).

The cause of a break or burnout is a thin wire that cannot withstand network surges and overloads. Say thanks to the Chinese, they are economical guys, they don’t want to wind thicker wire ...

Checking the health of the transformer is quite simple. It is necessary to measure the resistance of the primary and secondary windings. The resistance of the primary winding should be several units of kilo-ohms (1 kOhm = 1000 Ohms), the secondary - several tens of Ohms.

When checking the transformer, the resistance of the primary winding turned out to be equal to 1,8 kOhm, which indicates its integrity. There is no break.

For the secondary winding, the resistance was 25,5 Oh, that's okay too. The transformer was correct.

To get the correct winding resistance readings, you must adhere to the following rules:

When measuring touch the terminals only with the probes of the multimeter. It is unacceptable to take the current-carrying parts of the probes with both hands and take measurements, since the multimeter readings will infidels! I have already told you in detail about how to correctly measure the resistance with a multimeter.

Remember, the human body also has resistance and can shunt the resistance you are measuring. In this case, this is the resistance of the windings. This rule is true when measuring any resistance.

It is necessary to exclude the influence of the resistances of other parts. What does it mean? This means that the part must be isolated from other parts of the circuit, i.e. soldered from the board, disabled.

In case of repairing the adapter, it is recommended to unsolder the leads leading to the electronic circuit before measuring the resistance of the secondary winding. This will help eliminate the influence of the resistance of the electronic circuit on the measured resistance.

The diode bridge on discrete diodes VD1-VD4 serves to rectify the alternating current of the secondary winding. A common malfunction of a diode bridge is a “breakdown” of one or more diodes of which it consists.With such a malfunction, the diode turns into an ordinary conductor. Diodes are checked quite simply, you can not even solder them from the board, but measure the resistance of each of the diodes separately. If the diode is broken, then the multimeter will show a very low resistance (0 or units of ohms).

So that other elements of the circuit do not confuse the readings of the multimeter, it is better to remove one of the diode leads from the circuit. After checking, do not forget to solder it back.

Capacitors C1 and C2 serve to filter the voltage and are auxiliary elements of the stabilizer 78L12. The integral stabilizer 78L12 provides a stabilized voltage of 12V at the output of the power supply.

Resistor circuit R1 and LED VD5, serves to indicate the operation of the device. If any part of the circuit is faulty, for example, a transformer or a stabilizer on a 78L12 chip, then there will be no voltage at the output of the power supply and the VD5 LED will not light up. By its glow, you can immediately determine what the problem is. If it is lit, then the connecting wire is most likely interrupted. Well, if not, then the electronic filling of the power supply may be faulty.

Most often, transformer power supplies for active antennas fail due to burnout of the stabilizer on the 78L12 chip.

When repairing the power supply, the following sequence of actions should be followed:

If there is an indication (the LED is on), you should look for a malfunction in the wires through which voltage is supplied to the powered device. It is enough to “ring” the wires with a multimeter.

If there is no indication, the resistance of the primary winding of the transformer should be measured. This is easy to do, you can not even disassemble the power supply, but measure the resistance of the winding through the contacts of the power plug.

We disassemble the power supply, we make an external inspection. We pay attention to the darkened areas around the radio components, chips and cracks on the cases of the power stabilizer (78L12 or equivalent), swelling of the filter capacitors.

In the process of repairing the power adapter for the active antenna, it turned out that the 78L12 stabilizer chip was faulty. The electrolytic capacitor C1 (100uF * 16V) was also replaced with a capacitor with a larger capacity - 470uF (25V). When replacing a capacitor, the polarity of its inclusion in the circuit should be taken into account.

It is not necessary to know the pinout (location and purpose) of the 78L12 stabilizer pins. But, you need to remember, sketch or photograph the location of the faulty microcircuit on the printed circuit board. In this case, if you forget how the microcircuit was soldered to the printed circuit board, then you will already have a drawing or photo, by which it is easy to determine the correct installation of the element in the circuit.

An ordinary laptop power supply is a very compact and fairly powerful switching power supply.

In the event of a malfunction, many simply throw it away, and buy a universal PSU for laptops as a replacement, the cost of which starts from 1000 rubles. But in most cases, you can fix such a block with your own hands.

It's about repairing the power supply from an ASUS laptop. It's an AC/DC power adapter. Model ADP-90CD. Output voltage 19V, maximum load current 4.74A.

The power supply itself worked, which was clear from the presence of a green LED indication. The voltage at the output plug corresponded to what is indicated on the label - 19V.

There was no break in the connecting wires or breakage of the plug. But when the power supply was connected to the laptop, the battery did not start charging, and the green indicator on its case went out and glowed at half the original brightness.

It was also heard that the block beeps. It became clear that the switching power supply was trying to start, but for some reason either an overload occurs, or the short circuit protection is triggered.

A few words about how you can open the case of such a power supply.It is no secret that it is made airtight, and the design itself does not involve disassembly. To do this, we need several tools.

We take a manual jigsaw or a canvas from it. It is better to take a canvas for metal with a fine tooth. The power supply itself is best clamped in a vice. If they are not, then you can contrive and do without them.

Next, with a manual jigsaw, we make a cut deep into the body by 2-3 mm. in the middle of the body along the connecting seam. The cut must be done carefully. If you overdo it, you can damage the printed circuit board or electronic stuffing.

Then we take a flat screwdriver with a wide edge, insert it into the cut and split the body halves. No need to hurry. When separating the halves of the body, a characteristic click should occur.

After the power supply housing is opened, we remove the plastic dust with a brush or brush, we take out the electronic filling.

To inspect the elements on the printed circuit board, you will need to remove the aluminum heat sink bar. In my case, the bar was fastened to other parts of the radiator with snaps, and was also glued to the transformer with something like silicone sealant. I managed to separate the bar from the transformer with a sharp blade of a penknife.

The photo shows the electronic filling of our block.

It didn't take long to find the problem. Even before opening the case, I did test inclusions. After a couple of connections to the 220V network, something crackled inside the unit and the green indicator, signaling the operation, completely went out.

When examining the case, liquid electrolyte was found, which leaked into the gap between the network connector and the elements of the case. It became clear that the power supply stopped functioning properly due to the fact that the electrolytic capacitor 120 uF * 420V “slammed” due to the excess of the operating voltage in the mains 220V. Pretty common and widespread problem.

When dismantling the capacitor, its outer shell crumbled. Apparently lost its properties due to prolonged heating.

The safety valve at the top of the case is "bulging", a sure sign of a failed capacitor.

Here is another example with a faulty capacitor. This is another laptop power adapter. Pay attention to the protective notch in the upper part of the capacitor case. It opened from the pressure of the boiled electrolyte.

In most cases, bringing the power supply back to life is quite easy. First you need to replace the main culprit of the breakdown.

At that time, I had two suitable capacitors at hand. I decided not to install the SAMWHA 82 uF * 450V capacitor, although it was ideally sized.

The fact is that its maximum operating temperature is +85 0 C. It is indicated on its body. And given that the power supply housing is compact and not ventilated, the temperature inside it can be very high.

Prolonged heating has a very bad effect on the reliability of electrolytic capacitors. Therefore, I installed a Jamicon capacitor with a capacity of 68 uF * 450V, which is rated for operating temperatures up to 105 0 C.

It is worth considering that the capacitance of the native capacitor is 120 microfarads, and the operating voltage is 420V. But I had to put a capacitor with a smaller capacity.

In the process of repairing power supplies from laptops, I encountered the fact that it is very difficult to find a replacement for the capacitor. And the point is not at all in capacity or operating voltage, but in its dimensions.

Finding a suitable capacitor that would fit into a cramped case proved to be a daunting task. Therefore, it was decided to install a product that is suitable in size, albeit with a smaller capacity. The main thing is that the capacitor itself is new, of high quality and with an operating voltage of at least 420

450V. As it turned out, even with such capacitors, the power supplies work properly.

When soldering a new electrolytic capacitor, strictly observe the polarity terminal connections! As a rule, on the printed circuit board, next to the hole, there is a sign “+" or "–“.In addition, the minus can be marked with a black thick line or a mark in the form of a spot.

On the capacitor case on the side of the negative terminal there is a mark in the form of a strip with a minus sign “–“.

When you turn it on for the first time after repair, keep a distance from the power supply, because if you reverse the polarity of the connection, the capacitor will “pop” again. The electrolyte may get into the eyes. This is extremely dangerous! If possible, wear protective goggles.

And now I’ll tell you about the “rake”, which is better not to step on.

Before changing something, you need to thoroughly clean the board and circuit elements from liquid electrolyte. This is not a pleasant occupation.

The fact is that when an electrolytic capacitor pops, the electrolyte inside it breaks out under great pressure in the form of spray and steam. It, in turn, instantly condenses on the adjacent parts, as well as on the elements of the aluminum radiator.

Since the mounting of the elements is very tight, and the case itself is small, the electrolyte gets into the most inaccessible places.

Of course, you can cheat and not clean out all the electrolyte, but this is fraught with problems. The trick is that the electrolyte conducts electricity well. I have seen this from my own experience. And although I cleaned the power supply very carefully, I didn’t solder the throttle and clean the surface under it, I hurried.

As a result, after the power supply was assembled and connected to the mains, it worked properly. But after a minute or two, something crackled inside the case, and the power indicator went out.

After opening, it turned out that the remains of the electrolyte under the throttle closed the circuit. This caused the fuse to blow. T3.15A 250V on the input circuit 220V. In addition, everything was covered with soot at the short circuit, and the wire that connected its screen and the common wire on the printed circuit board burned out at the throttle.

The same throttle. Burnt wire repaired.

Short circuit soot on the PCB just below the throttle.

As you can see, it hit pretty hard.

The first time I replaced the fuse with a new one from a similar power supply. But when it burned down a second time, I decided to restore it. This is what the fuse looks like on the board.

And here's what's inside. He himself is easily disassembled, you just need to press the latches at the bottom of the case and remove the cover.

To restore it, you need to remove the remnants of the burnt wire and the remnants of the insulating tube. Take a thin wire and solder it in place of the native. Then assemble the fuse.

Someone will say that this is a "bug". But I don't agree. In the event of a short circuit, the thinnest wire in the circuit burns out. Sometimes even the copper tracks on the printed circuit board burn out. So in which case our self-made fuse will do its job. Of course, you can get by with a thin wire jumper by soldering it onto the contact pads on the board.

In some cases, to clean out all the electrolyte, it may be necessary to remove the cooling radiators, and with them active elements such as MOSFETs and dual diodes.

As you can see, liquid electrolyte can also remain under winding products, such as chokes. Even if it dries, then in the future, because of it, corrosion of the terminals may begin. A good example is in front of you. Due to electrolyte residues, one of the capacitor terminals in the input filter completely corroded and fell off. This is one of the laptop power adapters that I had for repair.

Let's go back to our power supply. After cleaning from electrolyte residues and replacing the capacitor, it is necessary to check it without connecting it to the laptop. Measure the output voltage at the output plug. If everything is in order, then we assemble the power adapter.

Needless to say, this is a very difficult task. First.

The cooling radiator of the power supply consists of several aluminum plates. Between themselves, they are fastened with latches, and also glued with something resembling silicone sealant. It can be removed with a penknife.

The upper radiator cap is attached to the main body with latches.

The bottom plate of the heatsink is fixed to the printed circuit board by soldering, usually in one or two places. An insulating plastic plate is placed between it and the printed circuit board.

A few words about how to fasten the two halves of the body, which at the very beginning we sawed with a jigsaw.

In the simplest case, you can simply assemble the power supply and wrap the halves of the case with electrical tape. But this is not the best option.

I used hot glue to glue the two plastic halves together. Since I don’t have a hot-melt gun, I cut off pieces of hot-melt glue from the tube with a knife and put them in the grooves. After that, I took a hot air soldering station, set about 200 degrees

250 0 C. Then I heated the pieces of hot glue with a hair dryer until they melted. I removed the excess glue with a toothpick and once again blew it with a soldering station hairdryer.

It is advisable not to overheat the plastic and generally avoid excessive heating of foreign parts. In my case, for example, the plastic of the case began to lighten with strong heating.

Despite this, it turned out very well.

Now I will say a few words about other malfunctions.

In addition to such simple breakdowns as a slammed capacitor or an open in the connecting wires, there are also such as an open inductor output in the line filter circuit. Here is a photo.

It would seem that it is a trifling matter, unwound the coil and soldered it into place. But it takes a lot of time to find such a malfunction. It is not immediately possible to find it.

Surely you have already noticed that large-sized elements, such as the same electrolytic capacitor, filter chokes and some other parts, are smeared with something like a white sealant. It would seem, why is it needed? And now it’s clear that with its help large parts are fixed, which can fall off from shaking and vibrations, like this very throttle, which is shown in the photo.

By the way, initially it was not securely fixed. Chatted - chatted, and fell off, taking the life of another power supply from the laptop.

I suspect that thousands of compact and rather powerful power supplies are sent to the landfill from such banal breakdowns!

For a radio amateur, such a switching power supply with an output voltage of 19 - 20 volts and a load current of 3-4 amperes is just a godsend! Not only is it very compact, it is also quite powerful. Typically, power adapters are rated at 40

Unfortunately, with more serious malfunctions, such as the failure of electronic components on a printed circuit board, the repair is complicated by the fact that it is quite difficult to find a replacement for the same PWM controller chip.

I can't even find a datasheet for a specific chip. Among other things, the repair is complicated by the abundance of SMD components, the marking of which is either difficult to read or it is impossible to purchase a replacement element.

It is worth noting that the vast majority of laptop power adapters are made very high quality. This can be seen at least by the presence of winding parts and chokes that are installed in the surge protector circuit. It suppresses electromagnetic interference. In some low-quality power supplies from stationary PCs, such elements may not be available at all.

The switching power supply is built into most household appliances. As practice shows, it is this node that quite often fails, requiring replacement.

The high voltage constantly passing through the power supply does not affect its elements in the best way. And it's not the fault of the manufacturers. By increasing the service life by mounting additional protection, it is possible to achieve the reliability of the protected parts, but lose it on newly installed ones. In addition, additional elements complicate the repair - it becomes difficult to understand all the intricacies of the resulting scheme.

Manufacturers solved this problem radically, reducing the cost of the UPS and making it monolithic, non-separable. Such disposable devices are becoming more and more common.But, if you are lucky - the collapsible block failed, self-repair is quite possible.

The principle of operation for all UPSs is the same. The differences relate only to schemes and types of parts. Therefore, it is quite simple to understand the breakdown, having fundamental knowledge in electrics.

For repair you will need a voltmeter.

It measures the voltage across an electrolytic capacitor. It is highlighted in the photo. If the voltage is 300 V, the fuse is intact and all other elements associated with it (mains filter, power cable, input chokes) are in good order.

There are models with two small capacitors. In this case, the normal functioning of the mentioned elements is indicated by a constant voltage of 150 V on each of the capacitors.

In the absence of voltage, you need to ring the diodes of the rectifier bridge, the capacitor, the fuse itself, and so on. The insidiousness of the fuses is that, having failed, they outwardly do not differ in any way from the working samples. It is possible to detect a malfunction only through a continuity - a blown fuse will show high resistance.

Having found a faulty fuse, you should carefully examine the board, as it often fails at the same time as other elements.

• power or rectifier bridge (looks like a monolithic block or may consist of four diodes);
• filter capacitor (looks like a large block or several blocks connected in parallel or in series) located in the high-voltage part of the block;
• transistors mounted on a radiator (these are field workers - power switches).

Important. All parts are soldered and replaced at the same time! Replacement in turn will lead each time to burnout of the power unit.

For certain purposes, a switching power supply can be assembled independently from improvised parts. Read more about this here.

Burnt items must be replaced with new ones. The radio market offers a rich assortment of parts for power supplies. Finding good options at the lowest prices is quite easy.

• voltage drops;
• lack of protection (there is a place for it, but the element itself is not installed - this is how manufacturers save money).

Solution this malfunction of switching power supplies:

• install protection (it is not always possible to find the right part);
• or use a mains voltage filter with good protective elements (not jumpers!).

Another common cause of a power supply malfunction has nothing to do with the fuse. We are talking about the absence of output voltage with a fully serviceable such element.
Solution:

1. Swollen capacitor - soldering and replacement is required.
2. A failed choke - it is necessary to remove the element and change the winding. The damaged wire is unwound. In this case, the turns are counted. Then a new wire of suitable section is wound for the same number of revolutions. The item is returned to its place.
3. Deformed bridge diodes are replaced with new ones.
4. If necessary, the parts are checked by a tester (if no damage is visually detected).

It is quite possible to build a hot air soldering station yourself. A fan is used as a supercharger, and a coil is used as a heater. The best option for a temperature controller for a soldering iron is a circuit with a thyristor.

Causes of failure:

• do not block the ventilation openings;
• provide optimal temperature conditions - cooling and ventilation.

Things to Remember:

1. The first connection of the unit is made to a lamp with a power of 25 watts. This is especially important after replacing diodes or a transistor! If a mistake is made somewhere or a malfunction is not noticed, the passing current will not damage the entire device as a whole.
2. When starting work, do not forget that electrolytic capacitors retain a residual discharge for a long time. Before soldering parts, it is necessary to short-circuit the capacitor leads. You cannot do this directly. Short through a resistance greater than 0.5V.

If the transformer adapter is broken, can you fix it yourself?

How to fix the power adapter with your own hands?

To repair the power adapter yourself at home, you must have at least:

In a transformer adapter, the circuit is simple, therefore, having at least basic knowledge in electronics and logical thinking, it is possible to fix it. Most often fail: protection (limiting resistor), capacitors, transformer. If the transformer is out of order, it is easier to buy a new block.

First you need to “ring out” the primary winding of the transformer. If it does not “ring”, then try carefully, so as not to damage the winding, remove the adhesive tape. Find the ends of the wire and ring again. If the winding is intact, then it is safe to say that the fuse in the primary winding has blown. It looks like a small square with two pins. One output is soldered to the winding wire of the primary, the second - to the pole of the power plug. In this case, you can insert our fuse in its place or, in extreme cases, short-circuit the blown fuse.

If the primary does not ring at all, then there is only a rewind of the transformer.

If the primary is ringing, but the PSU is not working, then we first measure the voltage on the secondary, with the transformer turned on to the network. Naturally, without forgetting the precautions.

It is advisable to carry out measurements on the secondary by soldering the rectifier from the terminals. If there is voltage, repair the rectifier and stabilizer. If there is no voltage, rewind the secondary of the transformer.

Of course you can. The device of the transformer power supply is quite simple: a transformer, a rectifier, a smoothing capacitor and a stabilization circuit. The simplest knowledge in the field of electronics is enough to detect a malfunction and eliminate it. First of all, you ring the transformer, that all its windings are intact and not shorted. Next, call the rectifier bridge diodes and check the smoothing capacitor. If everything is in order, the stabilization circuit should receive a voltage that can be measured. Then you deal with the stabilization scheme itself, visually inspecting and checking the elements. First of all, you should make sure that there are no non-solders or cracks in the T-shirt, and then deal with the rest.

It is practically impossible to repair a modern power adapter. There, in addition to the transformer itself, there is a bunch of semiconductor electronics. If any of this electronics burns out, you will find out what exactly. And if the wiring is also damaged somewhere, then such a product has a place in the non-ferrous metal.

To independently repair the power supply, adapter, you need some skills in working with electronics and with a soldering iron.

So, you need a soldering iron, a screwdriver, a multimeter. We unscrew the fixing screws and remove the cover of the power supply.

Usually, the power supply breaks down when it breaks through a rectifier diode bridge, which is located in a high-voltage circuit. To diagnose such a breakdown, you need a voltmeter or multimeter. It is necessary to measure the voltage on all wires coming out of the unit. If there is no minimum voltage, it is necessary to measure the resistance between any two terminals of the diode bridge. To do this, you need to buy a rectifier bridge, which is designed for voltage. 300 V and a current of 1 A.

After we soldered a new diode bridge, we check the diodes that are included in the secondary rectifier circuits. For this test, disconnect the power supply from the motherboard. If there is a “standby” minimum voltage, but the unit itself works intermittently, jerkily, then the defect is in the converter. Using an ohmmeter, we are looking for a faulty diode - in this case, it will have no resistance on both sides. The diode assembly and the broken diode need to be replaced.

In principle, most often this is already enough to return the power supply to working condition. But such a repair is only possible if we have the required parts, or they can be bought at a price that does not exceed the cost of a new power supply.Sometimes it makes sense to buy just a new unit and supplement it with a surge protector.

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Message dtvims » Thu Sep 25, 2014 4:51 pm

In general, it is more correct to call it: Repair of chargers for laptops, etc. for dummies! (Many letters.)
Actually, since I myself am not a professional in this field, but I successfully repaired a decent pack of PSU data, I think that I can describe the technology as a “kettle to a teapot”.
Main theses:
1. Everything you do at your own peril and risk is dangerous. Start under voltage 220V! (here you need to draw a beautiful lightning).
2. There are no guarantees that everything will work out and it is easy to make things worse.
3. If you double-check everything several times and DO NOT neglect security measures, then everything will work out the first time.
4. All changes in the circuit should be made ONLY on a completely de-energized PSU! Completely unplug everything!
5. DO NOT grab the PSU connected to the network with your hands, and if you bring it close, then only one hand! As a physicist used to say at our school: When you climb under voltage, you need to climb there with only one hand, and with the other hand hold yourself by the earlobe, then when you are twitched by the current, you pull yourself by the ear and you will no longer want to climb under voltage again.
6. We replace ALL suspicious parts with the same or complete analogues. The more we replace, the better!

TOTAL: I do not pretend that everything said below is true, because I could confuse / not finish something, but following the general idea will help to understand. It also requires minimal knowledge of the operation of electronic components, such as transistors, diodes, resistors, capacitors, and knowledge of where and how the current flows. If some part is not very clear, then you need to look on the net or in textbooks for its basis. For example, the text mentions a resistor for measuring current: we are looking for “Methods for measuring current” and we find that one of the measurement methods is to measure the voltage drop across a low resistance resistor, which is best placed in front of the ground so that on one side (ground) is Zero , and on the other hand, a small voltage, knowing which, according to Ohm's law, we get the current passing through the resistor.

Message dtvims » Thu Sep 25, 2014 5:26 pm

The options are schematic below. Voltage is applied to the input, we connect the repaired PSU to the output.

Option 3, I have not personally tested. This is a 30V step down transformer. A 220V light bulb will no longer work, but it is possible without it, especially if the transformer is weak. In theory, there should be a way to work. In this embodiment, you can safely climb into the PSU with an oscilloscope, without fear of burning anything.

And here is a video on the subject: