DIY impulse power supply repair

In detail: DIY impulse power supply repair from a real master for the site my.housecope.com.

We repair a switching power supply, power supply, voltage converter ourselves, with our own hands. Malfunctions. Self-repair.

Repair of a switching power supply. Any person with basic electronic skills can independently repair a power supply or voltage converter. Proceed to identify the problem and rectify it. (10+)

We repair the switching power supply ourselves, with our own hands. Malfunctions

Attention! Some elements of the power supply are under mains voltage during operation. Make sure you are qualified to safely repair the switching power supply.

Diagnostics and repair of a switching power supply in most cases can be performed with basic skills in electronics.

For your attention a selection of materials:

PRaktika design of electronic circuits Art of design of devices. Element base. Typical schemes. Examples of finished devices. Detailed descriptions. Online calculation. Possibility to ask a question to the authors

Such a power supply consists of a high-voltage and a low-voltage part.

In the high-voltage section, the mains voltage is rectified and charges the filter capacitor. Thus, a constant voltage of about 310 volts is obtained. Further, this voltage is converted into pseudo-rectangular oscillations with a frequency of 10 - 100 kHz, which makes it possible, using small-sized pulse transformers, to convert into a low-voltage voltage with minimal losses.

In the low-voltage part, the incoming voltage with a frequency of 10 - 100 kHz is rectified, filtered and fed to the load. In addition, there are control and feedback circuits that provide the formation of the desired signals and maintain the stability of the output voltage.

Video (click to play).

When looking at a power supply board, it is usually easy to visually understand where the high voltage part is and where the low voltage part, since standards require these parts to be separated from each other at some distance in order to ensure the safety of the user. The high-voltage part is where the mains wire goes. The low voltage part is where the load wires come from.

Most household devices contain switching power supplies built on the basis of two circuit solutions - half-bridge and single-ended forward. See the diagram.

Not every power supply can be repaired. Now manufacturers proceed from the assumption that the power supply is a separate non-separable element that must be replaced as a whole - a monolithic module. Such a power supply unit can simply be sealed and non-separable. However, most power supplies can still be disassembled and repaired.

In my experience, 40% of faults are due to the breakdown of the diode in the input network bridge or filter capacitor, 30% - to the breakdown of the power switch - a transistor or field-effect transistor in the high-voltage part, 15% - to the breakdown of power rectifier diodes in the low-voltage part, 10% - on burning of the throttle of the output filter. The other 5% of cases are not worth thinking about. In these cases, we carry the unit to the workshop or replace it as a whole.

The first two cases are usually manifested by burnout of the input fuse. The third and fourth are manifested in the absence of an output voltage in the presence of an input voltage and a working fuse.

We open the converter. Checking the fuse. We draw a conclusion.

If the fuse is defective, then, most likely, the input bridge, filter capacitor or power switch has burned out. We examine the block board. A defective high voltage filter capacitor is usually easy to spot visually. On breakdown, it collapses or swells. It can also be removed and checked with a tester. It is necessary to solder and check immediately both the input power bridge (it can be either monolithic or consist of free-standing diodes) and the filter capacitor (such a large electrolytic capacitor in the high-voltage part, or maybe a block of capacitors connected in parallel or in series), and power switches / one power switch for a single-cycle version (these are transistors or field switches installed on the radiator). We change everything that has burned out. If you check and change one part at a time, then with each new check, the entire power section can burn out again and again.

Replacement parts are easy to buy now. Take the time to find a seller with the lowest price. Prices can vary up to three times.

Replace the fuse, turn it on gently. It should work. If it doesn't work, we take it to the workshop or just buy a new unit.

Why do the elements of the high-voltage part burn out? Due to power surges. Power supplies must provide a protection circuit against such surges. Manufacturers lay it down, otherwise they will not pass certification, so there is a place and holes for it on the board. But for the sake of economy, they do not put it. The presence on the board in the high-voltage part of the place with empty holes and a jumper above them tells us about this problem. To avoid new problems, you can choose the right security elements and install them, but this is quite difficult. It's easier to leave everything as it is, and power the device through a good mains voltage filter. In general, it is better to power all electronic devices at home through such filters. Only the filter should be really good; there should be protective elements in it, and not jumpers.

Most likely, the rectifier diode is broken, or the filter choke in the output, low-voltage part of the circuit has burned out. Electrolytic capacitors may still be pierced. The breakdown of capacitors is clearly visible during visual inspection for swelling or deformation; you will not miss a burnt choke either. The diode will have to be removed and checked with a tester. Capacitors and diodes must be replaced with new ones. The choke can be rewound. To do this, you need to take it out, disassemble it, wind up the burnt wire, counting the turns. Wind the required number of turns with a new wire of a suitable diameter. Install the throttle in place.

Such a malfunction arises from the fact that the temperature regime of the unit is violated. For example, it is installed in a place where there is no normal ventilation, cooling. Install your equipment so that it is well ventilated and cooled. Do not block the ventilation openings.

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If it was not possible to visually establish the defective part, then it is necessary to sequentially check the performance of the fuse, diodes, electrolytic capacitors and transistors. Unfortunately, if the control microcircuits are out of order, their malfunction can be established only indirectly - when, with completely serviceable discrete elements, the operational state of the power supply does not occur.

The most common reasons for the inoperability of television units are:

breakage of ballast resistance;
inoperability (short circuit) of the high voltage filter capacitor;
malfunction of the secondary voltage filter capacitors;
breakdown or burnout of rectifier diodes.

All these parts (except for rectifier diodes) can be checked without removing them from the board. If it was possible to identify the faulty part, then it is replaced and they begin to check the repair performed. To do this, an incandescent lamp is installed in place of the fuse and the device is connected to the network.

Several options for the behavior of the repaired device are possible here:

The light flashes and goes out, the sleep mode LED lights up, a raster appears on the screen. In this situation, the line scan voltage is measured first. If its value is too high, it is necessary to check and replace electrolytic capacitors with guaranteed serviceable ones. A similar situation manifests itself in the event of a malfunction of the optocouplers.
If the lamp flashes and goes out, the LED does not light up, the raster is absent, then the pulse generator does not start. In this case, the voltage level on the electrolytic capacitor of the filter of the high-voltage part is checked. If it is below 280.0 ... 300.0 volts, then the following malfunctions are most likely:
- one of the rectifier bridge diodes is broken;
- large capacitor leakage (the capacitor is "old").

If there is no voltage, it is necessary to re-check the continuity of the supply circuits and all diodes of the high voltage rectifier.

If the light is high, you must immediately disconnect the power module from the network and re-check all electronic parts.

The above sequence and test scheme allow you to identify the main malfunctions of the power supply device of the television receiver.

Today, ATX devices of various capacities are most widely used for powering desktop (desktop) designers. The reason for their repair should be:

the motherboard does not start (the computer is completely inoperative);
the cooling fan of the device itself does not rotate;
the block “tries” to start itself many times.

Before starting the repair of ATX devices, it is necessary to assemble the load circuit (figure). The repair is carried out in the following sequence:

the device is removed from the computer and the cover is removed from it;
a vacuum cleaner and a brush removes dust from electronic boards and surfaces of parts;
external examination of electronic elements and printed circuit boards;
a load device is connected.

If, when turned on, the lamp flashes brightly and continues to burn, then the diode bridge in the high-voltage part or the filter capacitor is out of order. Burnout of the high-voltage transformer is possible.

If the fuse is intact, then the reason for inoperability may be:

failure of the transistors of the pulse generator;
malfunction of the PWM controller.

In these cases, it is easier to purchase a new device, which, depending on the capacity, costs from 600 to 800 rubles.

With repeated self-starting of the device, the reason for inoperability is usually the failure of the reference voltage stabilizer. In this case, the computer system cannot pass the self-test mode, it turns off and turns on the power module.

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

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

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

The principle of operation is the same for all UPSs. The differences concern only schemes and types of parts. Therefore, it is quite simple to understand the breakdown, having basic knowledge of electrical engineering.

You will need a voltmeter for repairs.

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 related elements (power filter, power cable, input chokes) are in good order.

There are models with two small capacitors. In this case, the normal functioning of these elements is evidenced 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. The fault can only be detected through a dial tone - a blown fuse will show a high resistance.

Having found a faulty fuse, you should carefully inspect the board, since 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 installed on the radiator (these are field switches - power switches).

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

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

Burnt-out elements 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 pretty easy.

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

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 (no jumpers!).

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

Swollen Condenser - Desoldering and replacement required.
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 a suitable section is wound on the same number of turns. The part is returned to its place.
Deformed bridge diodes are replaced with new ones.
If necessary, the parts are checked with a tester (if no damage is detected visually).

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

Breakdown reasons:

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

Things to Remember:

The first connection of the unit is made to a 25-watt lamp. This is especially important after replacing diodes or 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.
When starting work, do not forget that a residual discharge remains on electrolytic capacitors for a long time. Before soldering the parts, it is necessary to short-circuit the capacitor leads. You cannot do this directly. It should be short-circuited through a resistance with a nominal value higher than 0.5 V.

Nowadays, almost all household electrical appliances have special devices called pulse units. They can take the form of both a separate module and a board located in the device structure.Since impulse units are designed to rectify and lower the mains voltage, they can often fail. Therefore, in order not to buy a new expensive household device, knowledge of how to fix it with your own hands will be quite in demand. This article will tell you how to identify malfunctions of this device or board, as well as how to repair it yourself.The switching power supply unit can be in the form of a board or an independent external module.It is intended, as already mentioned, to lower and rectify the mains voltage. Its need is based on the fact that there is a voltage of 220 volts in the standard power supply network, and for the operation of many household appliances, a much lower value of this parameter is required.
Today, instead of standard buck-rectifier circuits, assembled on the basis of a diode bridge and a power transformer, pulse voltage conversion power supplies are used.Note! Despite the presence of high circuit reliability, switching power supplies often break down. Therefore, in our time, the repair of these elements of electrical circuits is very relevant. Image - DIY impulse power supply repair

Switching power supply circuit

All types of impulse power supply (built-in or outside the device) have two functional blocks:

high voltage. In such a power supply unit, the mains voltage is converted to DC using a diode bridge. Moreover, the voltage is smoothed to the level of 300.0 ... 310.0 volts across the capacitor. As a result, the high voltage is converted into a pulse voltage with a frequency of 10.0 ... 100.0 kilohertz;

Note! Such a device of the high-voltage unit made it possible to abandon the use of low-frequency massive step-down transformers.

low voltage. Here there is a decrease in the impulse voltage of an unnecessary level. In this case, the voltage is smoothed and stabilized.

As a result of such a structure, at the output from the pulse-type power supply unit, several or one voltage is observed, which is needed to power household appliances.
It should be noted that the low-voltage unit can contain a variety of control circuits that increase the reliability of the device.

Switching power supply (board). The colors are shown in the diagram

Since power supplies of this type have a complex device, their correct DIY repair should rely on some knowledge in electronics.
When repairing this device, do not forget that some of its elements may be under mains voltage. In this regard, even during the initial inspection of the unit, utmost care must be taken.
Repair in most cases will not cause complications, because switching power supplies have a typical device. Therefore, their malfunctions will also be similar, and do-it-yourself repair looks quite a feasible task.

Faults that cause a switching power supply to be inoperative can appear for a variety of reasons. Most often, breakdowns occur due to:

the presence of fluctuations in the mains voltage. A malfunction can be caused by those oscillations for which these buck-rectifier modules are not designed;
connection to the power supply unit of loads for which household appliances are not designed;
lack of protection. By not installing protection, some manufacturers simply save money. If you find such a problem, you just need to install protection in a specific place where it should be located;
non-observance of the rules and recommendations of operation, which are indicated by the manufacturers for specific models.

At the same time, in recent years, a frequent reason for the breakdown of voltage converters is a factory defect or the use of low-quality parts during assembly. Therefore, if you want your purchased switching power supply to work as long as possible, you should not buy it in questionable places and not from trusted people. Otherwise it might just be wasted money.
After diagnosing the unit, the following malfunctions are often found:

40% of cases - disruption of the high-voltage part. This is evidenced by the burnout of the diode bridge, as well as the breakdown of the filtering capacitor;
30% - breakdown of a bipolar (forming high-frequency pulses and located in the high-voltage part of the device) or power field-effect transistor;
15% - breakdown of the diode bridge in its low-voltage part;

All other breakdowns can only be identified with special equipment, which is unlikely to be kept at home by the average person. For a deeper and more accurate test, a digital voltmeter and an oscilloscope are required. Therefore, if the breakdowns do not lie in the four options above, then at home you will not be able to fix a power supply of this type.
As you can see, do-it-yourself repairs in this situation can have a wide variety of forms. Therefore, if your computer or TV stopped working due to a breakdown of the power supply, then you do not need to run to the repair service, but you can get involved in solving the problem on your own. At the same time, home repairs will cost significantly less. But if you cannot cope with the task on your own, then you can already bow to the specialists from the repair service.

Any repair always begins with finding out the reason for the failure of the impulse power supply.

Note! To repair and troubleshoot a switching power supply, you need a voltmeter.

In order to identify it, you must adhere to the following algorithm:

disassemble the power supply;
using a voltmeter, we measure the voltage that is available on the electrolytic capacitor;

Measuring the voltage across an electrolytic capacitor

if the voltmeter gives out a voltage of 300 V, this means that the fuse and all the elements of the electrical network (power cable, mains filter, input chokes) associated with it are working normally;
in models with two small capacitors, the voltage indicating their serviceability, which is given by a voltmeter, should be 150 V for each device;
if there is no voltage, then it is necessary to carry out a continuity of the diodes of the rectifier bridge, fuse and capacitor;

Note! The most insidious elements in the electrical circuit of a pulse-type power supply are fuses. No external signs indicate their breakdown. Only a dial tone will help you identify their malfunction. In case of combustion, they will give out high resistance.

Switching power supply fuses

if a fuse was found to be faulty, then you need to check the rest of the electrical circuit elements, since they rarely burn out alone;
outwardly, it is quite easy to identify a damaged capacitor. It usually swells or collapses. Repair in this case will consist in soldering it and replacing it with a workable one.
It is imperative to ring the following elements for serviceability:
rectifier or power bridge. It looks like a monolithic block or is organized from four diodes;

Power bridge of impulse power supply unit

filter capacitor. It can look like one or more blocks that are connected in series or in parallel. Usually the filter capacitor is located in the high-voltage part of the unit;
transistors located on the heat sink.

Pay attention! When carrying out repairs, you need to find all the faulty parts of the switching power supply at once, since they should be soldered and replaced at the same time! Otherwise, the replacement of one element will lead to burnout of the power section.

For a standard type of device, the above stages of diagnostics and repair work will be identical. This is due to the fact that they all have a typical structure.

Soldering parts to the board

Also, in order to carry out a high-quality self-repair of a pulse voltage converter, you need a good soldering iron, as well as the ability to handle it. In this case, you still need solder, alcohol, which can be replaced with refined gasoline, and flux.
In addition to the soldering iron, you will definitely need the following tools for repair:

Screwdriver Set;
tweezers;
household multimeter or voltmeter;
incandescent lamp. Can be used as ballast load.

With such a set of tools, simple repairs will be within the power of any person.

If you are going to repair a damaged pulse voltage converter with your own hands, you need to understand that such manipulations are not carried out for products intended for complex replacement. They are not designed for repair and not a single master will undertake to repair them, since here you need a complete dismantling of the electronic filling and replacing it with a new working one.

Board power supply switching principle of operation

In all other cases, repair at home and with your own hands is quite possible.
Correct diagnostics is half of the repair. Malfunctions associated with the high-voltage part can be easily detected both visually and using a voltmeter. But a fuse malfunction can be detected in the absence of voltage in the area after it.
If it detects malfunctions with its help, it remains to simply make their simultaneous replacement. When carrying out repair work, it is imperative to rely on the appearance of the electronic board. Sometimes, in order to check every detail, you need to unsolder it and test it with a multimeter. It is advisable to check all details. Despite the difficulty of such a process, it will allow identifying all damaged elements of the electrical circuit and replacing them in time in order to prevent burnout of the device in the foreseeable future.

Replacing burnt-out parts

After all the burnt-out parts have been replaced, it is necessary to install a new fuse and check the repaired power supply by turning it on. Usually, if everything has been done correctly, and all norms and instructions for repair work are observed, the converter will work.

Repair of a power supply unit operating on a pulse principle can be fully implemented with your own hands. But for this, you need to correctly diagnose the device, and also replace all burned-out parts of the electrical circuit at the same time. By following all the recommendations, you can easily carry out the necessary repair actions at home.

If your computer's power supply fails, do not rush to get upset, as practice shows, in most cases, repairs can be done on your own. Before proceeding directly to the technique, we will consider the block diagram of the power supply unit and provide a list of possible malfunctions, this will greatly simplify the task.