How to repair a computer power supply yourself. How to repair a computer power supply yourself

Repairing computer hardware on your own is quite difficult. At the same time, the user must know exactly which of all the components needs repair. It makes sense to repair the computer's power supply if it is (at least) removed from the warranty, and also - the cost of replacement makes such a repair really worthwhile. High-quality repairs in the SC can cost up to the cost of "budget" PSU. Usually, the user can do something himself ... Provided that he has the skills to work with electrical equipment (220 Volts), and well understands the danger of mistakes in such work.

Recommendations for self-repair of computer power supplies:

1. Any power supply unit must be connected to a 220 V network through a "fast" fuse for a current of no more than 2A.
2. First launch after renovation works produced in series with an incandescent lamp. A short circuit at the input of the device will be indicated by the incandescence of the lamp. Such a power supply unit cannot be connected to the network.
3. In the process of both diagnostics and repairs, it is necessary to discharge all electrolytic containers (after each turn on / off). You need to wait 3-5 minutes, or use a 220V electric lamp - the flash will indicate that the discharge has actually been made.
4. All repair operations are carried out with the power supply completely disconnected from the mains.

It is advisable that there are no grounded objects near the workplace (such as: heating radiators, pipes, etc.)

Actually, we will not "climb" into the high-voltage part of the power supply circuit. Independent repair is reduced to: search for "ring" cracks; replacement of power diodes (if necessary); replacement of "bad" capacitors (if necessary).

In any case, the repair of a computer power supply begins with its dismantling from the PC. Of course, this is worth doing if you are 100% sure that it is the PSU that needs to be repaired.

Disassembly of the power supply case itself is carried out by unscrewing the screws (screws) that fasten the two halves to each other. A Phillips screwdriver is used.

Note: by disassembling the power supply yourself, you damage the manufacturer's seal - which will void the further warranty for this device.

Directly about how the power supply is repaired and about the main malfunctions is described below. More often than not, the failures that occur can be detected and eliminated quite simply:

• Check if there is a "standby" voltage (+ 5V SB). This is the purple wire from the 24-pin (main) PSU connector. Between "black" and "violet" there should be a voltage of +5 Volts. You can check its presence before disassembling the block case, while the power supply itself must be connected to the network.

• Dismantled the power supply - we look at the board. Faulty (swollen) electrolytic capacitors are common. This can be determined visually, most often it is electrolytic capacitors of not very large capacity (470-220 μF, and less) that are susceptible to the defect. Such a capacitor must be unsoldered from the board (for this, it will have to be removed), and the new one must be of the same capacity and designed for the same (or higher) voltage. Attention: respect the polarity of the leads! On imported ones, the "strip" is marked with a "minus".

• The next malfunction is the failure of low-voltage diodes (12 or 5V). They can be constructively made as assemblies of two diodes (flat case with three leads), there is also a separate installation.

• Checking / replacing diodes is a little more complicated than capacitors. To check, you need to solder one pin of each diode (you can - and the whole part). Everybody knows how a working diode "rings". With a direct connection, the tester will show a value (close to "0"), with the opposite - it does not show anything (the tester itself is switched on in the "diode" mode):

• For replacement, it is recommended to install Schottky diodes having a similar (or higher) declared current / voltage.

• When repairing the power supply yourself, unscrew the screws of the board itself and remove it (make sure again, the unit must be de-energized). Carefully looking at the installation, you can quickly notice the defects of "ring cracks":

They need to be "soldered", then - to collect and turn on everything (perhaps - everything will work).

Separately, it should be said about the "duty" food. As a rule, repairing a power supply unit by simply replacing burnt out transistors will not give any result - the transistors burn out again, and the same ones. A transformer may also be the culprit of the breakdown. This is a scarce part that is difficult to buy and find. In rare cases, the reason for the absence of 5V "standby" voltage may be a change in the operating frequency, for which the "frequency setting" parts are responsible: a resistor and a capacitor (not electrolytic).

Note: in order to solder the part installed on the heat sink, first dismantle (unscrew) its fastener. Installation - done in reverse order (first - fastening, then - soldering). Try not to break the insulation of the part from the heat sink (usually mica is used).

Power supply startup: check for + 5V SB. If it is, we will try to start the power supply unit (connect the "light green" wire, PS-ON, with the "black", common).

On this, the user's possibilities for self-repair, one might say, are exhausted.

Attention! Do not repair the power supply yourself if you have no experience in electrical engineering! After each disconnection, it is necessary to discharge the high-voltage capacitors (wait 3-5 minutes)!

Read more: "swollen" capacitors and their replacement

We hope that from the photo it is clear which capacitors are "swollen" and which are not.

If there are several identical ones on the board (or - a set of parallel-connected ones), of which at least one is "swollen", it is better to change everything. Firms producing reliable products: Nichicon, Rubycon. But you are unlikely to find such. From the budget, you can recommend Teapo, Samsung.

When installing, it is necessary to observe the polarity (operating voltage - must be the same or more than indicated on the replaced one).

The photo shows a 16 Volt capacitor, 470 MicroFarad (Rubycon, the most expensive series).

Soldering technology

When assembling and dismantling parts on the PCB board, it is recommended to use a 40 W soldering iron. In some cases, for bulky parts ("powerful" leads), you can use a soldering iron and 60 watts (but - no more).

The simplest solder (like POS-60) is suitable in this case. Better to take in the form of a thin wire.

Flux - not used (it is enough to have ordinary rosin available).

Dismantling part:

• Heat with a soldering iron until the solder is completely melted;
• Using a desoldering device (made of plastic), quickly pump out the liquid solder:

• Repeat steps 1 and 2.

Correctly sealed part, easily exits the board on its own (no need to "press" the output with a soldering iron).

If the capacitor is dismantled, you can first "bite off" the protruding output with side cutters.

If unsoldered power element - it is necessary to completely unscrew the fastening screw.

Replacing the fuse

In the circuit of any power supply unit, the fuse goes immediately after the power outlet (in series with one of the 220 V phases). The fuses themselves, as parts, differ in current strength (that is, how many amperes it will withstand at maximum). Also, fuses are divided into "F" -type ("fast"), "T" -type ("thermal").

If the fuse needs to be replaced, you must find out what rating (amperage) it was designed for. Also, it is advisable to know the "type".

Replacing with a fuse with a higher rating is not allowed. Replacing F with T is the same.

Note: if you know what "current" is needed, but do not know the "type", you can install a new type "F" fuse.

Exactly. And so that there are no questions why it burns out more often, it will still be easier to find out reliable data (both denomination and type).

If the fuse is in a glass cylindrical case, then in any case it is designed for 220V power supply. The use of other types of construction is not allowed.

What is used (devices and materials)

When repairing a computer power supply , you don't need any "non-standard" devices or equipment:

But what is in fig. - implies that you at least know how to handle: soldering iron, tester (tongs, side cutters ...). For professional repairs, an oscilloscope was supposed to be here (3 MHz bandwidth is enough). That's just its price ... (like 2-3 new power supplies).

Hopefully, the information provided here will be useful for performing an “initial” repair. More complex operations (repair of a transformer, work with high-voltage "piping", restoration of generation) are within the power of professionals (who have experience in repairing power supply units).

A switching power supply is not a very "simple" device; in some cases, restoration of viability is made by a complete replacement of parts (of a particular unit). A more complex, "independent" repair is not obliged to "be crowned with success" in every case ...

Diode characteristics

The diode itself, as a separate element, is of one of three types: just a diode ( p-n junction), Microwave diode, and Schottky diode (quantum). We are only interested in the last one.

The task of the diode is to pass current in one direction (and not to pass it in the other). If the voltage drop in direct connection on conventional diodes is 1 or 2 volts, then on Schottky diodes it is close to zero. The voltages obtained in a computer PSU are low (12 volts and 5), which is why only Schottky is used.

You can see what the voltage drop across the diode is equal to. The tester must be in diode mode (as mentioned above). If he "shows" from 0.015 to 0.7 - then everything is correct. Such values \u200b\u200bare typical for a Schottky diode (less is already a "breakdown").

Inside the power supply circuits, a pair of diodes is used, including their opposite:

For a positive voltage - use "assemblies" (three-pin, they have 2 diodes). Single diodes (round body) - usually used to generate negative voltages. When replacing single diodes (even if one "flew"), it is recommended to replace "a pair".

What is the best way to choose a replacement? If on the "rectangular" plastic case (3-pin) - the brand is written:

That, with "round" - will be more difficult. The stripe on the body only means “direction”.

If we know the brand of diodes - we are looking for the same, or - we look at the parameters (voltage, current), and look for an analogue (with the same or slightly higher value).

If we don’t know - well, we need to "download" the diagram of your power supply and see. By the way, in the SC they also do this (but thinking, guessing what current strength is there is not a very rewarding occupation). Not forgetting that computer power supplies contain only Schottky diodes.

Note: it is not recommended to install diode assemblies / diodes with deliberately large current and voltage parameters (for example: it was 50 Volts 12 A, but they put 50 Volts 20 A). You do not need to do this, because: there may be a different body. Besides, there are “additional” parameters (which, in a more “powerful” case, differ “not for the better”).

Typical example (assemblies, low-power PSU): 12CTQ040 (40V, 12A); 10CTQ150 (150V, 10A).

An example of single diodes: 90SQ045 (45V, 9A); SR350 (50V, 3A).

Replacing the PSU fan

How to choose a new PSU fan? It, that is, the fan, must be: with a hydro-bearing, three-pin (3 wires in the cable), and - of suitable dimensions (12cm / 8cm).

It is also important that a low-speed "vent" is used in the PSU, usually 1200-1400 (for 12 cm) and 1600-2000 (for 8).

When the power supply unit starts, not all voltage (not 12 Volts) is supplied to the fan, but, let's say, 3-5 Volts. It is important that the fan is able to "start" at such voltages (otherwise, it will not spin up after switching on). Check the "starting voltage" of the fan, be careful.

How to connect the fan to the PSU:

1. Two wires (black, red) are soldered to the power supply board.
2. Two wires (black, red) are connected with a 2-pin connector to the board connector.
3. Three wires (black, red + yellow) are connected with a 3-pin connector to the board.

In the first two cases, the yellow wire - the tachometer - can be removed from the power supply case for monitoring by the motherboard itself.

Pay attention to such parameter as fan height. If you take more than you need, the power supply case will not close.

When replacing, it is important that the performance of the new fan (in "liters per minute") is at least the same as that of the old fan. Perhaps this parameter is the main one (in the product description, it is usually indicated).

Thus, you can immediately carry out the "mod" of the power supply by installing an equally productive, but quieter propeller (hydro-bearing in budget power supplies - not often "by default").

That's probably all that can be said about the fans. Take your pick.

Equivalent load

The power supply, when started by "wiring", started. Don't rush to install it on your computer. Let's try to test the power supply unit at an equivalent load.

The following resistors are taken:

They are called "PEV" (the brand of copper wire from which they are made). You can take at 25 watts, or 10 (at 7.5):

The main thing here is to make a diagram of them (connecting: in parallel, in series) to get a "powerful" resistance (3 Ohms and 5-6 Ohms).

5-ohm load, we will include in the "12V" line, 3-ohm - to "5V". To connect to the PSU, a Molex connector is used (the yellow wire is 12 V):

Note: when creating an "equivalent", take into account the power that falls on each resistor (it should not exceed the value for which it is designed).

Knowing the voltage across the resistor, the power is found according to the law: voltage squared / resistance.

Example: 4 resistors of 20 Ohm - "in parallel", the power of each - 7.5 watts (will go for testing the "12-volt" line)

You can also use halogen bulbs for 12V (let's say: two 10 Watt, in parallel).

So, having connected the dummy load to the Molex connector, we try to turn on the power supply unit ("light green" / "black", ATX connector). The 220 Volt cord must also be "regular".

If the switch is on, wait 10 seconds. Is the block going into defense? The fan should rotate, all voltages should be within the required range (a deviation of no more than 5-6% is allowed).

Actually, in such a “sparing” mode for it, any power supply unit should work as long as you like.

A more powerful "equivalent" could be made. That is, resistance in Ohms will be even lower. The main thing is not to overdo it (for each power supply unit, the maximum current is indicated):

The current through the load is equal to the voltage divided by its resistance (in ohms). Well, this - you already know ...

During testing, the "load" will be included in only two lines ("plus 5", "plus 12"). This is generally enough. Other voltages ("minuses") can be measured with a voltmeter (on a 24-pin plug).

Note: if you want to "test" the "+12" line with a current strength higher than 6A - do not use Molex connectors! 4-pin processor power connector (+ 12V) - Holds up to 10 Amps. If necessary, the load is "spread" between two connectors (processor, "molex").

Note 2: When making any connections, use a wire of sufficient size (1 mm2 - current 10 A)

At the equivalent load, heat will be generated (heat power is equal to electrical power). Take care of cooling (air flow). During testing, the first 2-3 minutes - it is better to monitor if one of the resistors overheats.

The photo shows a “serious” approach to creating an “equivalent”.

Power supply repair

A long-purchased computer begins to work intermittently over time, some parts wear out, break down and need to be repaired or replaced.

Perhaps the biggest problem most often arises with the cooler on the power supply.

Due to a breakdown or a long service life, it starts to work hard, the power supply or laptop overheats. In this case, the repair of the cooler cannot be delayed until the last, otherwise it may simply burn out.

A fan is a device that works specifically to cool all the microcircuits and particles of the power supply, and if it is defective, each part will wear out faster, and accordingly, the breakdown will occur much earlier than the period specified in the warranty.

To troubleshoot or repair a cooler, first of all, you need to with a possible reason and pay attention to its operation.

Most often there are 2 problems with the cooler:

1. The cooler does not spin and does not cool;

2. The fan makes a lot of noise during operation.

These problems are solved in the same way. To repair the breakdown, you need to remove the power supply, unscrew and disassemble into parts, and lubricate the faulty cooler.

Often the cause of its breakdown is the ingress of a large lump of dust or small debris, as well as an already established factory lubricant.

In order to repair the cooler, you must:

Disconnect the power supply unit from the mains, pull it out to a convenient area. Remove the cover of the system unit from the side, but not the one where the motherboard is located.

Put the power supply on the other side, disconnect the power connectors. After that, you need to unscrew 4 bolts from the back of the block, pull it out, and remove 4 protective screws.

Removing the cover will open the fan. It needs to be blown out with air, you can use cold air from a hair dryer. At this stage, you need to get rid of the dust. Now it needs to be disconnected from the block. To do this, unscrew 4 screws.

The removed cooler must be cleaned from dust with a brush. There is a sticker in the middle of the fan, under which the "plug" is hidden. This label should be lifted slightly to make room for lubrication.

You need to remove the cap, cut off some of the plastic cover, and apply a small amount of machine oil to the ring. Lube can be purchased at any hardware store.

You need to shake the fan lightly so that the engine oil spreads. If it gets inside the cooler, you need to add some more oil.

If you do not want to remove the plastic, you can use a syringe with a fine needle.

Now you need to assemble the fan: glue the plastic protective cover, fasten all the screws and bolts, put everything in place and insert all the cables.

The cooler on the power supply is broken - buy a new one

If the user has not had the opportunity to repair such things before, it would be best to contact a specialist. If, after the repair work, the cooler still makes noise or does not spin, this is a sure sign that it needs to be replaced with a new one. You can buy a power supply unit for a computer here - http://sunmart.com.ua/kompyutery-i-po/bloki-pitaniya Choosing a new fan, it is better to take it from the same company as before. It is best to clean and lubricate the fan by watching the video, this will be an illustrative example and you can easily do everything you need to replace with a new one.

When choosing a new fan, it is better to take it from the same company as before. The best way to clean and lubricate the fan is by watching the video, this will be a good example and you can easily do everything yourself.

Self-repairing a computer power supply is a rather complicated matter. Having taken up this, you should clearly understand which component needs repair. Also, it should be understood that if the device is under warranty, then after any intervention, the warranty card will immediately expire.

If the user has little skills in working with an electrical appliance and is sure that he will not make mistakes, then you can safely take on such work. Remember to be careful when working with an electrical appliance.

Computer power supply circuit

To create a galvanic isolation, a large amount of winding is required. Based on this, a computer requires a very large power and it is natural that such a transformer for a PC should be large and heavy.

But due to the frequency of the current that is required to create the magnetic field, much fewer turns are required on the transformer. Thanks to this, when using the converter, small and light power supplies are created.

Power Supply - at first glance, a rather complicated device, but if a not particularly serious breakdown occurs, then it is quite possible to repair it yourself.

Below is a standard power supply circuit. As you can see, there is nothing complicated, the main thing is to do everything in turn so that there is no confusion:

Necessary repair tools

In order to start self-repairing a power supply unit, you should have the necessary tools at hand.

First you need to arm yourself with devices for computer diagnostics:

• working power supply unit;
• post card;
• memory bar in working order;
• compatible type of video card;
• cPU;
• multimeter;

For the very same repair, you will need more:

• and everything for soldering;
• screwdrivers;
• the computer is in working order;
• oscilloscope;
• tweezers;
• insulating tape;
• pliers;

Naturally, this is not so much for a perfect repair, but this is enough for home repairs.

Step-by-step instruction

So, armed with all the necessary tools, you can start repairing:

1. First of all, you need to disconnect the system unit from the network and let it cool down a little.
2. All 4 screws are unscrewed one by one, that secure the back of the computer.
3. The same operation is carried out for the side surfaces. This work is done carefully so as not to touch the wires of the block. If there are screws that are hidden under the stickers, they must also be unscrewed.
4. After the case is completely removed, The PSU will need to be purged (you can use a vacuum cleaner). You do not need to wipe anything with a damp cloth.
5. The next step there will be careful consideration and finding the cause of the problem.

In some cases, the power supply unit fails due to the microcircuit. Therefore, you should carefully examine its details. Particular attention should be paid to the fuse and the capacitor.

Often, the cause of a power supply failure is swelling of capacitors, which break down due to poor cooler performance. This whole situation is easily diagnosed at home. It is enough just to carefully examine the top of the capacitor.

swollen capacitors

A convex lid is an indicator of fracture. In ideal condition, a capacitor is a flat cylinder with flat walls.

To eliminate this breakdown you will need:

1. Extract broken capacitor.
2. In its place a new serviceable part similar to the broken one is installed.
3. Cooler is removed, its blades are cleaned from dust and other particles.

To avoid overheating your computer, blow it out regularly.

In order to check the fuse in another way, it is not necessary to unsolder it, but rather connect the copper core to the contacts. If the power supply unit starts to work, then it is enough just to solder the fuse, perhaps it just moved away from the contacts.

To check the fuse is working, just turn on the power supply. If it burns out a second time, then you need to look for the cause of the breakdown in other details.

The next breakdown option may depend on the varistor. It is used to allow current to flow and equalize it. Signs of its malfunction are traces of carbon deposits or black spots. If such were found, the part must be replaced with a new one.

varistor

Note! The varistor is the part of the computer that is checked when it is turned on, so you need to be careful and attentive. Each individual part is checked according to a similar principle: resistors, capacitor.

It should be noted that checking and replacing diodes is not an easy task. To check them, you should evaporate each diode separately or the whole part at once. They should be replaced with similar parts with the stated voltage.

If, after replacing the transistors, they burn out again, then the cause should be looked for in the transformer. By the way, this part is hard enough to find and buy. In such situations, experienced craftsmen recommend buying a new PSU. Fortunately, such a breakdown is rare.

Another reason for the breakdown of the power supply unit may be associated with ring cracks that break the contacts. This can also be detected visually by carefully examining the printed strip. You can eliminate such a defect with a soldering iron by performing a thorough soldering, but you must be good at soldering. With the slightest mistake, you can break the integrity of the contacts and then you will have to change the entire part as a whole.

ring cracks

If a more complex breakdown is found, then excellent technical training is required. Also, you will have to use complex measuring instruments. But it should be noted that the purchase of such devices will cost more than the entire repair.

You should be aware that the elements that require replacement are sometimes in short supply and not only are they difficult to obtain, they are also expensive. If a complex breakdown occurs and the repair costs exceed the price compared to purchasing a new power supply. In this case, it will be more profitable and more reliable to purchase a new device.

Functional check

After the reasons that brought the power supply out of the operating mode are eliminated, it must be checked.

The most elementary operation Is to turn on the computer to the network. But, by the way, this can be done without connecting a PC. It is enough to connect any load to the power supply unit, for example a CD-ROM, after which you need to short-circuit the green and black wires in the power supply connector and turn it on.

If everything is in order, then the fan and the drive LED on the working power supply will immediately turn on. And naturally, the reverse reaction of the power supply unit (if nothing started working), then the cause has not been eliminated.

After the serviceability of the device is confirmed, you can start assembling the system unit.

Before you undertake an independent repair of the power supply, you must be confident enough in your knowledge of electrical appliances:

1. To start you can read the literature, which can be easily found on the Internet, where the causes and symptoms of a power supply breakdown are described in detail.
2. We need to study the scheme.
3. Beforethan to start disassembling the system unit, make sure that it is disconnected from the network. It will be better if it is completely chilled.
4. Dust and any dirt must be blown out with a vacuum cleaner or hair dryer. It is not recommended to use a damp cloth.
5. Study should be carried out alternately all the details. It is advisable to check the power supply every time.
6. If you do not have the skills to work with a soldering iron, but soldering is indispensable, it is better to consult a specialist, it will be cheaper.
7. When, if spare parts and repairs are more expensive than a new PSU, then it is better to think about purchasing a new part.
8. Before, how to start repairing the power supply, you need to make sure that the power cable and switch are working.

Signs of a Broken Power Supply

The power supply will not malfunction from scratch. If there are signs that indicate its malfunction, then before starting the repair, you should first eliminate the causes that led to its failure.

The reasons:

1. Poor quality supply voltage (voltage drops).
2. Not very high quality components Components.
3. Defects, which were approved at the factory.
4. Bad installation.
5. Parts arrangement on the plate of the power supply unit is located in such a way that it leads to contamination and overheating.

Signs:

1. The computer may not turn on, and if you open the system unit, you can find that the motherboard is not working.
2. PSU can and work, but the operating system does not start.
3. When turning on the PC everything seems to start working, but after a while everything turns off. This could trip the power supply protection.
4. The appearance of an unpleasant odor.

The failure of the power supply unit cannot be missed, since problems begin with turning on the system unit (it does not turn on at all), or after a few minutes of operation it turns off.

If at least one of the problems is noticed, you should think about eliminating the malfunction, otherwise, the computer may fail altogether, and then you cannot do without the intervention of an experienced specialist.

Major problems:

1. The most common momentthat can affect the operation of the power supply is the swelling of the capacitor. A similar problem can be determined only after opening the power supply unit and completely inspecting the capacitor.
2. If at least 1 diode fails, then the entire diode bridge also fails.
3. Burning resistors, which are located near capacitors, transistors. If such a problem occurs, then it will be necessary to look for the problem in the entire electrical circuit.
4. Problems with the PWM controller. It is quite difficult to check it, for this you need to use an oscilloscope.
5. Power transistors also fail frequently. A multimeter is used to check them.

Note! Power capacitors tend to hold a charge for some time, therefore it is not recommended to touch them with bare hands after the power is turned off. Also, remember that when the power supply is connected to the network, you do not need to touch the stove or radiator.

Repair cost

If you perform an independent repair of the power supply and do not have at hand necessary tools, then first of all you will have to spend money on their purchase. This amount can reach from 1000 rubles to 5000 rubles.

As for the power supply itself, everything depends on the parts that have become unusable. On average, repairs can cost up to 1,500 thousand rubles.

For your information: a used power supply unit in good condition can cost 2,000 - 2,500 rubles. This applies to models for older computers. Modern PCs are equipped with more expensive power supplies.

In a service center, a similar procedure can cost about the same amount. But at the same time, it should be remembered that a specialist always gives a guarantee for his work.

Computer power supply (PSU) Is an independent pulse electronic device designed to convert AC voltage into a series of constant voltages (+3.3 / +5 / +12 and -12) to power the motherboard, video card, hard drive and other computer units.

Before proceeding with the repair of the computer power supply, you need to make sure that it is faulty, since the inability to start the computer may be due to other reasons.

The photo appearance a classic ATX power supply unit of a stationary computer (desktop).

Where is the power supply unit in the system unit and how to disassemble it

To gain access to the computer's power supply unit, you must first remove the left side wall from the system unit by unscrewing the two screws on the back wall from the side of the connectors.

To remove the power supply from the case of the system unit, you must unscrew the four screws marked in the photo. To conduct an external inspection of the power supply unit, it is enough to disconnect from the computer units only those wires that interfere with the installation of the power supply unit on the edge of the system unit case.

Having located the power supply on the corner of the system unit, you need to unscrew the four screws on the top, in the photo in pink. Often one or two screws are hidden under the sticker, and to find the screw you have to peel it off or pierce it with a screwdriver tip. On the sides, there are also stickers that prevent you from removing the cover, they need to be cut along the line of mating of the parts of the power supply case.

After the cover is removed from the power supply unit, all dust must be removed with a vacuum cleaner. It is one of the main reasons for the failure of radio components, since covering them with a thick layer reduces the heat transfer from the parts, they overheat and, working in difficult conditions, fail faster.

For reliable operation of the computer, it is necessary to remove dust from the system unit and power supply unit, as well as check the operation of coolers at least once a year.

Block diagram of the power supply unit of the ATX computer

A computer power supply is a rather complex electronic device and its repair requires deep knowledge of radio engineering and the availability of expensive devices, but, nevertheless, 80% of failures can be eliminated on your own, having the skills of soldering, working with a screwdriver and knowing the structural diagram of the power source.

Almost all power supply units of computers are made according to the structural diagram below. Electronic components in the diagram, I have given only those that most often fail, and are available for independent replacement by non-professionals. When repairing an ATX power supply, you will definitely need color coding of the wires leaving it.

The power supply is supplied by the power cord through a plug connection to the power supply board. The first element of protection is the Pr1 fuse usually stands at 5 A. But, depending on the power of the source, there may be a different rating. Capacitors C1-C4 and choke L1 form a filter that serves to suppress common-mode and differential noise that occurs as a result of the operation of the power supply itself and can come from the network.

Surge protectors assembled according to this scheme are installed without fail in all products in which the power supply unit is made without a power transformer, in TVs, VCRs, printers, scanners, etc. The maximum filter efficiency is possible only when connected to a network with a ground wire. Unfortunately, cheap Chinese computer power supplies often lack filter elements.

For example, the capacitors are not installed, and instead of the choke, the jumpers are soldered. If you are repairing the power supply and find that the filter elements are missing, then it is advisable to install them.

Here is a photo of a high-quality power supply unit of the computer, as you can see, the board has filtering capacitors and an interference suppression choke.

To protect the power supply circuit from power surges in expensive models, varistors (Z1-Z3) are installed, in the photo on the right side in blue. Their principle of operation is simple. At normal mains voltage, the resistance of the varistor is very high and does not affect the operation of the circuit. If the voltage in the network rises above the permissible level, the resistance of the varistor decreases sharply, which leads to a blown fuse, and not to the failure of expensive electronics.

To repair a failed unit due to overvoltage, it will be enough to simply replace the varistor and fuse. If there is no varistor at hand, then you can do only by replacing the fuse, the computer will work normally. But at the first opportunity, in order not to risk it, you need to install a varistor in the board.

Some models of power supplies provide the ability to switch for operation with a supply voltage of 115 V, in which case the contacts of the switch SW1 must be closed.

For a smooth charge of electrolytic capacitors C5-C6, connected immediately after the VD1-VD4 rectifier bridge, an RT thermistor with a negative TCS is sometimes installed. In a cold state, the resistance of the thermistor is a few ohms, when a current passes through it, the thermistor heats up, and its resistance decreases 20-50 times.

To be able to turn on the computer remotely, the power supply unit has an independent, additional low-power power supply, which is always on, even if the computer is turned off, but the electrical plug is not removed from the outlet. It forms a voltage of +5 B_SB and is built according to the scheme of a transformer self-oscillating blocking generator on one transistor, powered from a rectified voltage by diodes VD1-VD4. This is one of the most unreliable parts of the power supply unit and it is difficult to repair it.

The voltages required for the operation of the motherboard and other devices of the system unit at the exit from the voltage generation unit are filtered from noise by chokes and electrolytic capacitors and then, through wires with connectors, are supplied to the consumption sources. The cooler, which cools the power supply itself, is powered, in old PSU models from a voltage of minus 12 V, in modern ones from a voltage of +12 V.

ATX computer power supply repair

Attention! To avoid damaging the computer, undocking and connecting the connectors of the power supply and other units inside the system unit should be performed only after the computer has been completely disconnected from the mains (remove the plug from the socket or turn off the switch in the Pilot).

The first thing to do is to check the presence of voltage in the socket and the serviceability of the Pilot extension cord by the glow of its switch button. Next, you need to check that the computer's power cord is securely plugged into the "Pilot" and the system unit and that the switch (if any) on the back of the system unit is turned on.

How to find a power supply malfunction by pressing the "Start" button

If power is supplied to the computer, then at the next step, looking at the cooler of the power supply (visible behind the grill on the back of the system unit), press the “Start” button of the computer. If the blades of the cooler move even a little, it means that the filter, fuse, diode bridge and capacitors of the left side of the structural diagram are in good working order, as well as an independent low-power supply +5 B_SB.

In some PSU models, the cooler is on the flat side and to see it, you need to remove the left side wall of the system unit.

Turning a small angle and stopping the cooler impeller when pressing the "Start" button indicates that for a moment output voltages appear at the output of the power supply unit, after which the protection is triggered, stopping the operation of the power supply unit. The protection is configured in such a way that if the current value for one of the output voltages exceeds the specified threshold, then all voltages are turned off.

An overload is usually caused by a short circuit in the low-voltage circuits of the power supply itself or in one of the computer units. A short circuit usually occurs when a breakdown occurs in semiconductor devices or insulation in capacitors.

To determine the node in which the short circuit has occurred, you need to disconnect all the power supply connectors from the computer blocks, leaving only those connected to the motherboard. Then connect the computer to the mains and press the "Start" button. If the cooler in the power supply unit is spinning, then one of the disabled nodes is faulty. To identify a faulty node, you need to connect them in series to the power supply.

If the power supply unit connected only to the motherboard does not work, you should continue troubleshooting and determine which of these devices is faulty.

Computer power supply check
measuring the resistance value of the output circuits

When repairing a power supply unit, some types of its malfunction can be determined by measuring the resistance value between the black GND common wire and the rest of the output connectors with an ohmmeter.

Before starting measurements, the power supply unit must be disconnected from the mains, and all its connectors are disconnected from the nodes of the system unit. The multimeter or tester must be turned on in the resistance measurement mode and the 200 Ohm limit must be selected. Connect the common wire of the device to the contact of the connector to which the black wire fits. The end of the second probe is in turn touching the contacts, in accordance with the table.

The table shows generalized data obtained as a result of measuring the resistance value of the output circuits of 20 serviceable power supply units of computers of different capacities, manufacturers and years of manufacture.

To be able to connect a power supply unit for testing without load inside the unit, load resistors are installed at some outputs, the value of which depends on the power of the power supply unit and the manufacturer's decision. Therefore, the measured resistance can fluctuate over a wide range, but should not be lower than the permissible value.

If the load resistor is not installed in the circuit, then the ohmmeter readings will change from a small value to infinity. This is due to the charging of the filtering electrolytic capacitor from the ohmmeter and indicates that the capacitor is serviceable. If you swap the probes, a similar picture will be observed. If the resistance is large and does not change, then there is probably a capacitor in the open circuit.

Resistance less than permissible indicates the presence of a short circuit, which can be caused by a breakdown of insulation in an electrolytic capacitor or rectifying diode. To determine the faulty part, you will have to open the power supply and unsolder one end of the filter choke of this circuit from the circuit. Next, check the resistance before and after the throttle. If after it, then a short circuit in the capacitor, wires, between the tracks of the printed circuit board, and if before it, then the rectifier diode is broken.

Troubleshooting the power supply by external inspection

Initially, you should carefully inspect all parts, paying particular attention to the integrity of the geometry of the electrolytic capacitors. As a rule, due to the severe temperature conditions, electrolytic capacitors fail most often. About 50% of power supply failures are due precisely to the failure of capacitors. Often, swollen capacitors are the result of poor cooler performance. The cooler bearings are lubricated and the speed drops. The cooling efficiency of the power supply parts decreases and they overheat. Therefore, at the first signs of a power supply cooler malfunction, additional acoustic noise usually appears, you need to clean it from dust and lubricate the cooler.

If the capacitor body is swollen or traces of leaked electrolyte are visible, then the failure of the capacitor is obvious and it should be replaced with a serviceable one. The capacitor swells in case of insulation breakdown. But sometimes, there are no external signs of failure, and the level of output voltage ripple is greater. In such cases, the capacitor is faulty due to the lack of contact between its terminal and the plates inside it, as they say, the capacitor is open. You can check the capacitor for an open circuit using any tester in the resistance measurement mode. The technology for testing capacitors is presented in the article "Measuring Resistance" on the site.

Further, the remaining elements, fuse, resistors and semiconductor devices are examined. A thin metal wire, sometimes with a thickening in the middle, should pass in the fuse inside along the center. If the wire is not visible, then most likely it has burned out. To accurately check the fuse, you need to ring it with an ohmmeter. If the fuse is blown, it must be replaced or repaired. Before making a replacement, to check the power supply, you can not solder the blown fuse from the board, but solder a vein of copper wire with a diameter of 0.18 mm to its terminals. If the wiring does not burn out when the power supply is turned on, then it makes sense to replace the fuse with a serviceable one.

How to check the health of the power supply by closing the contacts PG and GND

If the motherboard can only be checked by connecting to a known working power supply, then the power supply can be checked separately using a load block or started by connecting the +5 V PG and GND contacts together.

From the power supply unit to the motherboard, supply voltages are supplied using a 20 or 24 pin connector and a 4 or 6 pin connector. For reliability, the connectors have latches. In order to remove the connectors from the motherboard, you need to press the latch upward with your finger at the same time, applying quite a lot of effort, swinging from side to side, pull out the counterpart.

Next, you need to short-circuit each other, with a piece of wire, you can also use a metal paper clip, two leads in the connector removed from the motherboard. The wires are located on the side of the latch. In the photographs, the location of the jumper is indicated in yellow.

If the connector has 20 contacts 14 (the wire is green, in some power supplies it may be gray, POWER ON) and the output 15 (black wire, GND).

If the connector has 24 contacts, then you need to connect the output 16 (green green, in some power supplies the wire may be gray, POWER ON) and the output 17 (black wire GND).

If the impeller in the cooler of the power supply rotates, then the ATX power supply can be considered operational, and, therefore, the reason for the inoperative computer is in other blocks. But such a check does not guarantee the stable operation of the computer as a whole, since the deviations of the output voltages may be greater than the permissible ones.

Computer power supply check
measuring voltages and ripple levels

After repairing the power supply unit or in case of unstable operation of the computer, for complete confidence in the serviceability of the power supply unit, it is necessary to connect it to the load unit and measure the level of output voltages and the ripple range. The deviation of the voltage values \u200b\u200band the ripple amplitude at the output of the power supply unit should not exceed the values \u200b\u200bgiven in the table.

You can do without a load block by measuring the voltage and ripple level directly at the terminals of the power supply connectors in a running computer.

Table of output voltages and ripple swing of PSU ATX
Output voltage, V	+3,3	+5,0	+12,0	-12,0	+5.0 SB	+5.0 PG	GND
Wire color	orange	red	yellow	blue	violet	gray	the black
Permissible deviation,%	± 5	± 5	± 5	± 10	± 5	–	–
Permissible minimum voltage	+3,14	+4,75	+11,40	-10,80	+4,75	+3,00	–
Allowable maximum voltage	+3,46	+5,25	+12,60	-13,20	+5,25	+6,00	–
Ripple swing, no more, mV	50	50	120	120	120	120	–

When measuring voltages with a multimeter, the “minus” end of the probe is connected to the black wire (common), and the “plus” end to the required pins of the connector.

Voltage +5 V SB (Stand-by), purple wire - generates an independent low-power power supply built into the power supply unit, made on one field-effect transistor and a transformer. This voltage ensures that the computer operates in standby mode and serves only to start the power supply unit. When the computer is running, the presence or absence of +5 V SB does not matter. Thanks to +5 V SB, the computer can be started by pressing the "Start" button on the system unit or remotely, for example, from an uninterruptible power supply unit in the event of a prolonged lack of 220 V.

Voltage +5 V PG (Power Good) - appears on the gray wire of the power supply unit in 0.1-0.5 seconds if it is working properly after self-testing and serves as an enabling signal for the operation of the motherboard.

Voltage minus 12 V (blue wire) is only needed to power the RS-232 interface, which is absent in modern computers. Therefore, power supplies of the latest models may not have this voltage.

How to replace a fuse in a computer power supply

Typically, computer power supplies have a tubular glass fuse rated at 6.3 A. For reliability and compactness, the fuse is soldered directly onto the PCB. For this, special fuses are used with leads for sealing. The fuse is usually installed horizontally next to the line filter and is easy to spot by its appearance.

But sometimes there are power supplies in which the fuse is installed in an upright position and a heat shrink tube is put on it, as in the photo above. As a result, it is difficult to detect it. But the inscription on the printed circuit board next to the fuse helps: F1 - this is how the fuse on electrical circuits... Next to the fuse, the current for which it is designed can also be indicated, on the presented board the current is 6.3 A.

When repairing the power supply and checking the vertically installed fuse with a multimeter, a break was found. After dissolving the fuse and removing the heat-shrinkable tube, it became obvious that it had blown. The inside of the glass tube was covered with a black coating from the burned-out wire.

Fuses with wire leads are rare, but they can be successfully replaced with conventional 6.3 ampere fuses by soldering single-core pieces of copper wire with a diameter of 0.5-0.7 mm to the cups from the ends.

All that remains is to solder the prepared fuse into the printed circuit board of the power supply and check it for operation.

If the fuse burns out again when the power supply is turned on, it means that there is a failure of other radioelements, usually a breakdown of the transitions in the key transistors. Repairing a power supply with such a malfunction requires high qualifications and is not economically feasible. Replacing a fuse rated for a higher protection current than 6.3A will not lead to a positive result. The fuse will blow anyway.

Search in the power supply unit for faulty electrolytic capacitors

Very often, a power supply failure, and as a result, the unstable operation of the computer as a whole, occurs due to the swelling of the electrolytic capacitor cases. To protect against explosion, notches are made at the end of the electrolytic capacitors. With an increase in pressure inside the condenser, the casing swells or ruptures at the notch and it is easy to find a failed condenser by this sign. The main reason for the failure of capacitors is their overheating due to a malfunctioning cooler or exceeding the permissible voltage.

The photo shows that the capacitor on the left side has a flat end, and the right one is swollen, with traces of leaked electrolyte. Such a capacitor is out of order and must be replaced. In the power supply, electrolytic capacitors on the +5 V power bus usually fail, since they are installed with a small voltage margin, only 6.3 V. I have met cases when all capacitors in the power supply along the +5 V circuit were swollen.

When replacing capacitors along the 5 V supply circuit, I recommend installing capacitors that are designed for a voltage of at least 10 V. The higher the voltage the capacitor is designed for, the better, the main thing is that it fits into the installation site in size. In the event that a capacitor with a high voltage does not fit because of its size, you can install a capacitor of smaller capacity, but designed for a higher voltage. All the same, the capacity of the capacitors installed at the factory has a large margin and such a replacement will not worsen the operation of the power supply and the computer as a whole.

It makes no sense to replace the electrolytic capacitors in the power supply if they are all swollen. This means that the output voltage stabilization circuit has failed, and a voltage exceeding the permissible voltage was applied to the capacitors. Such a power supply unit can be repaired only with professional education and measuring instruments, but such repairs are not economically feasible.

The main thing when repairing a power supply unit is not to forget that electrolytic capacitors have polarity. On the negative side of the capacitor case, there is a mark in the form of a wide light vertical strip, as shown in the photo above. On the printed circuit board, the hole for the negative terminal of the capacitor is located in the marking area of \u200b\u200bthe white (black) semicircle, or the hole for the positive terminal is indicated by a "+" sign.

Checking the throttle group stabilization BP ATX

If there is a sudden smell of smoke from the computer system unit, then one of the reasons may be overheating of the group stabilization choke in the power supply unit or a burnt winding of one of the coolers. However, the computer usually continues to function normally. If, after opening the system unit and inspection, all coolers rotate, then the throttle is faulty. The computer must be turned off immediately and repaired.

The photo shows the power supply unit of the computer with the cover removed, in the center of which the choke is visible, covered with green insulation, burnt on top. When I connected this power supply unit to the load and applied the supply voltage to it, then after a couple of minutes a thin plume of smoke came from the choke. The test showed that all output voltages are within tolerance and the ripple swing does not exceed the allowable one.

The current of all voltages supplying the computer passes through the choke and it is obvious that there was a violation of the insulation of the winding wires as a result of which they short-circuited among themselves.

The windings can be rewound onto the same core, but as a result of strong heating, the magnetodielectric of the core may lose Q-factor, as a result, due to high Foucault currents, it will heat up even with intact windings. Therefore, I recommend installing a new choke. If there is no analogue, then you need to count the turns of the windings, winding them on a burnt out choke, and wind them with an insulated wire of the same section on a new core. In this case, the direction of the windings must be observed.

Checking other PSU elements

Resistors and simple capacitors must be free from stains and deposits. Semiconductor housings must be intact, without chips or cracks. When self-repair it is advisable to replace only the elements shown in the structural diagram. If the paint on the resistor has darkened, or the transistor has collapsed, then it is meaningless to change them, since, most likely, this is a consequence of the failure of other elements that cannot be detected without devices. A darkened resistor case does not always indicate a malfunction. It is quite possible that only the paint has darkened, and the resistance of the resistor is normal.

When a very nasty buzzing or rattling sound starts coming from the computer's power supply, this is a sure sign that replacing the cooler (fan) in the power supply is not far off. But it happens that there is no way to replace it "this very second". And you can't leave it as it is for two reasons. The first is a nasty sound from the system unit (more precisely, the power supply). Second, the fan can simply jam at some point in time, and the power supply will burn out from overheating. And this is fraught with replacing half of the "filling" of the system unit, which will cost a pretty penny!

Lubrication of the fan (cooler) of the power supply.

For this procedure, we need a fairly simple set of tools:

• heat-resistant silicone grease or, at worst, machine oil;
• screwdriver (cross);
• scalpel or office knife;
• wide scotch tape;
• several toothpicks or matches;

This set of tools will be enough to lubricate the fan in the computer's power supply.

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There is nothing complicated in the procedure for removing the PSU from the computer case. Unscrew the bolts that hold the left side cover, slide it back and remove. After that, disconnect all the wires coming from the power supply unit to the boards and disks (be sure to remember what and where !!!). After that, on the outside of the computer on the back wall, unscrew the 4 bolts that screw the power supply itself.

And here is the power supply on the table. There are two most popular types of power supplies (based on the location of coolers). With 80mm fans (it is located on the back wall of the power supply, which looks outward) and 120mm diameter (installed on the PSU cover, which faces downward and into the system unit).

In both cases, the first action will be to open the power supply cover. To do this, unscrew the four bolts on the upper edge (in the figure). Then just pull the cover up.

Read also: The computer began to work loudly (hum)

After removing the cover, you can unscrew the fan itself.

If you have a large 120mm fan, then on the same cover that you just removed, unscrew the four screws holding the fan.

If you have a cooler with a diameter of 80mm - unscrew the same 4 self-tapping screws, but on the back of the power supply.

Then gently pry off the sticker from the back of the fan using a knife. Then, with the same knife, tidy and pull out the rubber stopper that covers the bearing, and add oil there. There should be very little of it - if only the bearing surface (the sleeve in which the fan axis rotates) is wetted. If you can't accurately measure the oil, it doesn't matter! Take a toothpick and sharpen the tip in the form of a narrow spatula with a knife. Then dip this spatula in oil and gently lubricate the bearing with it.