Power supply repair. Eating to “live”: how to check the computer power supply The high-voltage part of the PC power supply does not start
Computer won't turn on? In this material you will find the answer to the question: how to check the computer power supply.
The thesis solution to this problem is in one of our previous articles.
Read about how to check its performance in our article today.
Power supply (PSU) is a secondary power source (the primary source is a socket), the purpose of which is to convert alternating voltage to direct voltage, as well as provide power to computer nodes at a given level.
Thus, the power supply acts as an intermediate link between the electrical network and, accordingly, the performance of the remaining components depends on its serviceability and correct operation.
Causes and symptoms of power supply failure
As a rule, the reasons why power supplies fail can be:
low quality of network voltage (frequent voltage drops in the network, as well as its output beyond the operating range of the power supply unit);
low quality of components and manufacturing in general (this point is relevant for cheap power supplies);
You can determine whether the power supply or some other component has failed by the following signs:
after pressing the power button of the system unit, nothing happens - there is no light or sound indication, the cooling fans do not rotate;
the computer turns on every other time;
Checking the power supply can be done in several ways.
We will talk about the sequence of each check below, but now we will just limit ourselves to short information to understand what we will do.
The essence of the first method is to check the voltage supply and at this stage we perform a rough check to see whether there is voltage or not.
The second method is to check the output voltage; we have already mentioned that the voltage must be strictly within certain limits and deviation in any direction is unacceptable.
The third method is to visually inspect the power supply for swollen capacitors.
For ease of understanding, the algorithm for each check will be presented in the form of step-by-step instructions.
Checking the power supply voltage
Step 1.
Step 2.
Remember or, for convenience, take a photo of how the power is connected to each of the components (motherboard, hard drives, optical drive, etc.) after which they should be disconnected from the power supply.
Step 3. Find a paper clip. We will use a paper clip to close the contacts on the power supply, and if it is not at hand, a wire similar in length and diameter to the paper clip will do.
After this, the paper clip must be bent in the shape of the Latin letter “U”.
Step 4. Find the 20/24 pin power connector. This connector is very easy to find - it is a harness of 20 or 24 wires, respectively, that come from the power supply and are connected to the PC motherboard.
Step 5. Find the green and black wire connectors on the connector. You must insert a paperclip into the connectors to which these wires are connected.
The paper clip must be securely fixed and in contact with the corresponding connectors.
Step 6.
Step 7 Checking the functionality of the power supply fan. If the device is working and conducts current, then the fan located in the power supply housing should rotate when voltage is applied.
If the fan does not rotate, check the contact of a paper clip with the green and black connectors of the 20/24-pin connector.
As mentioned above, this check does not guarantee that the device is working. This test allows you to determine that the power supply turns on.
For a more accurate diagnosis, the following test must be performed.
Checking the correct operation of the power supply
Step 1. Turn off computer. It must be remembered that the computer's power supply operates with a voltage that is dangerous to humans - 220V.
Step 2. Open the side cover of the system unit.
Remember or, for convenience, take a photo of how the power is connected to each of the components (motherboard, hard drives, optical drive, etc.) after which they should be disconnected from the power supply.
Step 3. Find the 20/24 pin power connector.
This connector is very easy to find due to its larger size - it is a harness of 20 or 24 wires, respectively, that come from the power supply and are connected to the PC motherboard.
Step 4. Find the connectors of the black, red, yellow, pink wires on the 20/24 pin connector.
Step 5. Load the power supply. In the future, we will measure the output voltage of the power supply.
In normal mode, the power supply operates under load, providing power to the motherboard, hard drives, optical drives, and fans.
Measuring the output voltage of a power supply that is not under load can lead to a fairly high error.
Note! An external 12V fan, an optical drive or an old hard drive, as well as combinations of these devices, can be used as a load.
Step 6. Turn on the power supply. We supply power to the power supply (do not forget to turn on the power button on the power supply itself, if it was turned off in Step 1).
Step 7 Take a voltmeter and measure the output voltage of the power supply. We will measure the output voltage of the power supply unit on the pairs of wires specified in Step 3. The reference voltage value for the black and pink wires is 3.3V, black and red - 5V, black and yellow - 12V.
The deviation of the specified values is allowed in the amount of ±5%. So the voltage is:
3.3V should be within 3.14 - 3.47V;
5V should be within 4.75 - 5.25V;
12V should be between 11.4 - 12.6V.
Visual inspection of the power supply
Step 1. Turn off computer. It must be remembered that the computer's power supply operates with a voltage that is dangerous to humans - 220V.
Step 2. Open the side cover of the system unit.
Remember or, for convenience, take a photo of how the power is connected to each of the components (motherboard, hard drives, optical drive, etc.) after which they should be disconnected from the power supply.
Probably, many PC users have had to deal with such a situation, when the computer won't turn on
(does not respond to pressing the power button: the lights do not light up, the cooler fans do not start spinning). In this article we will tell you what to do when the PC shows no signs of life.
I think everyone understands what's important is find out the cause of the hardware malfunction (the problem is most likely in the hardware, because only BIOS is involved in the software at the initial stage of turning on the computer).
What should you do when your computer does not turn on?
First of all, you need to make sure that to the power supply(PSU) computerserved voltage .
For this:
- we check is the computer connected to the network?;
- check for functionality network filter(connect another known-good electrical device to the surge protector);
- we check Is the power supply turned on?(if it has an on/off button). In addition, the 110/220 Volt switch (if equipped) must be in the 220 V position;
- checking there is good contact between the power supply and the power cord;
- checking power cord system unit. It is necessary to connect the cable from the system unit to the monitor, for example. If the light on the monitor starts blinking, it means the cable is working.
If The power supply receives power, but the computer does not turn on, move on to the next point:
We check the functionality of the power supply itself.
How to check the power supply? We take a known-good power supply and connect it to the motherboard of your PC. There is nothing complicated here. If you are doing this for the first time, simply disconnect the cables from the power supply on the motherboard one by one and connect them from another power supply.
If you do not have another power supply, you must check the power supply manually. To do this, disconnect the wires from the power supply from the motherboard and close (using any conductive material: a paper clip, etc.) the green and black contacts (pins 14 and 15). After the circuit closes, the fan inside the power supply should start spinning. If the fan is silent and you did everything correctly, you need to replace the power supply (it is better to replace than to repair). However, remember if The power supply has failed, you also need to check all the components inside the system unit(motherboard, processor, hard drive...).
If the power supply turns on, check the voltage value, which is supplied to the motherboard (at the output of the power supply). We take a tester (voltmeter) and measure the voltage at the outputs of the power supply. In the technical documentation for the motherboard, we look for the voltages that are supplied to it and compare them with those that we received. If the voltage does not correspond to the norm, replacement (possibly repair) of the power supply is necessary.
If the power supply is working properly, move on to the next step.
Checking button state
Resetting BIOS settings. It can be done:
- using a jumper(a jumper that allows you to set the operating mode of the device by closing/opening several contacts) Clear CMOS— should be located next to the BIOS battery on the motherboard;
- removing the Bios battery.
Besides check the voltage of the BIOS battery. If the value fluctuates greatly around 3V, buy a new battery.
Computer won't turn on yet? We remove the motherboard from the system unit, clean from dust. We start the computer.
If after all the above steps the computer does not turn on, the problem is more expensive. We remove all components from the motherboard: processor, RAM modules, disconnect the hard drive and other elements. You need to leave the power supply, motherboard, and connected wires from the power/reset buttons. Turn on the computer. What do we see?
- The power supply fan does not rotate (or it starts and turns off after a few seconds of operation - the power supply protection is triggered) – The motherboard is faulty. We buy a new one or take it to a service center for diagnostics and repairs.
- The power supply fan is spinning (constantly). We conclude that the problem most likely does not lie in the motherboard.
Alternately connect components to the motherboard, which we extracted earlier. First we connect the system speaker. Next we connect:
CPU.
We insert the processor into the socket (socket for the processor) and install the processor cooler (do not forget to use thermal paste). After installing the CPU, turn on the PC. What do we see?
- The fans of the power supply and processor cooler are rotating - this means that the processor is working normally. You should also hear beeps from the system speaker (it is advisable to have a table of beeps for your BIOS version in order to recognize them. This article does not list BIOS beeps - so as not to confuse the reader, since different BIOS versions have their own set of beeps).
- fans stop a few seconds after starting, no beeps are heard – The processor causes a short circuit.
- fans stop a few seconds after starting, beeping sounds are heard – thermal protection against CPU overheating is triggered. Most likely you The processor cooler was installed incorrectly. We reinstall the processor cooling system. Does not help? The CPU needs to be replaced.
- Finally, disconnect the cooler from the processor and turn on the computer for a few seconds (up to five). After checking the CPU temperature by touching the processor with your finger. If the percent is cold - it has already served its purpose.
Random access memory (RAM, RAM).
Before installing the RAM, you must clean it from dust. In addition, use a screwdriver (lightly) to move along the contacts of the RAM connectors on the motherboard. Next, install the memory module in the appropriate slot. After installing the RAM, turn on the PC. What do we see?
- fans are spinning- it means that RAM module works fine. You should also hear beeps from the system speaker. We look at the table of BIOS sound signals (which, I hope, we stocked up in advance) - does the sound not indicate any problem? We install the remaining memory modules one by one, if available (the computer must be turned off). Let's check. It is possible that the RAM slot will be inoperative(we check by adding another RAM plate to this slot).
- the computer turns off immediately . You can hear sounds from the system speaker (look at the table of BIOS sound signals - they should indicate a RAM malfunction). Means, RAM module or connector is faulty. Since each motherboard has several RAM slots, it is not difficult to check what is faulty.
Video card
Before starting the test, clean the video card from dust using a special brush or blow it with a vacuum cleaner. We connect the video card to the connector. Turn on the computer. What do we see?
Precautionary measures.
Repairing switching power supplies is a rather dangerous task, especially if the fault concerns the hot part of the power supply. Therefore, we do everything thoughtfully and carefully, without haste, in compliance with safety precautions.
Power capacitors can hold a charge for a long time, so do not touch them with bare hands immediately after turning off the power. Under no circumstances should you touch the board or heatsinks while the power supply is connected to the network.
In order to avoid fireworks and preserve still living elements, you should solder a 100-watt light bulb instead of a fuse. If, when the power supply is turned on, the lamp flashes and goes out, everything is fine, but if, when turned on, the lamp lights up and does not go out, there is a short circuit somewhere.
The power supply should be checked after repairs are made away from flammable materials.
What tool will you need:
Soldering iron, solder, flux. A soldering station with power adjustment or a pair of soldering irons of different power is recommended. A powerful soldering iron is needed for soldering transistors and diode assemblies that are located on radiators, as well as transformers and chokes. Various small things are soldered with a soldering iron of lower power.
Screwdriver.
Side cutters. Used to remove plastic clamps that hold wires together.
Multimeter.
Tweezers.
100W light bulb.
Refined gasoline or alcohol. Used to clean the board from traces of soldering.
BP device.
What we will see when we open the power supply.
Pinout of the 24 pin connector and voltage measurement.
We will need knowledge of the contacts on the ATX connector to diagnose the power supply. Before starting repairs, you should check the voltage of the standby power supply; in the figure, this contact is marked in blue + 5V SB, usually this is a purple wire. If the duty station is in order, then you should check the presence of the POWER GOOD signal (+5V), in the figure this contact is marked in gray, PW-OK. Power good appears only after the power supply is turned on. To start the power supply, we close the green and black wires, as in the picture. If PG is present, then most likely the power supply has already started and the remaining voltages should be checked. Please note that output voltages will vary depending on the load. So, if you see 13 volts on the yellow wire, do not worry, it is likely that under load they will stabilize to the standard 12 volts.
If you have a problem in the hot part and need to measure voltages there, then all measurements must be carried out from the common ground, this is the minus of the diode bridge or power capacitors.
Visual inspection.
The first thing to do is open the power supply and perform a visual inspection.
If the power supply is dusty, clean it. We check whether the fan is spinning; if it is, then this is most likely the reason for the failure of the power supply. In this case, you should look at diode assemblies and DGS. They are most prone to failure due to overheating.
Next, we inspect the power supply unit for burnt elements, PCB darkened by temperature, swollen capacitors, charred DGS insulation, broken tracks and wires.
Primary diagnosis.
Before opening the power supply, you can try to turn on the power supply to be sure of the diagnosis. A correct diagnosis is half the treatment.
Malfunctions:
The power supply does not start, there is no standby voltage;
The power supply does not start, but the standby voltage is present. No PG signal;
BP goes into defense;
The power supply works, but it stinks;
Output voltages are too high or low.
Fuse.
If you find that a fuse has blown, do not rush to change it and turn on the power supply. In 90% of cases, a blown fuse is not the cause of the malfunction, but its consequence. In this case, first of all, you need to check the high-voltage part of the power supply, namely the diode bridge, power transistors and their wiring.
Thermistor.
The purpose of the thermistor is to reduce the inrush current when turned on. When a high-voltage pulse occurs, the thermistor resistance sharply decreases to fractions of an ohm and shunts the load, protecting it and dissipating the absorbed energy in the form of heat. When there is an overvoltage in the network, the thermistor sharply reduces its resistance, and the increased current through it burns out the fuse. The remaining elements of the power supply remain intact.
The thermistor fails due to voltage surges, such as thunderstorms. Thermistors also fail if you mistakenly switched the power supply to 110V operating mode. A failed thermistor is usually not difficult to identify. It usually turns black and cracks, and soot appears on the surrounding elements. The fuse usually blows along with the thermistor. The fuse can be replaced only after replacing the thermistor and checking the remaining elements of the primary circuit.
Diode bridge.
A diode bridge is a diode assembly or 4 diodes standing next to each other. You can check the diode bridge without desoldering by ringing each diode in the forward and reverse directions. In the forward direction, the current drop should be about 500mA, and in the reverse direction it should sound like a break.
Diode assemblies are measured as follows. We place the negative probe of the multimeter on the leg of the assembly with the “+” mark, and use the positive probe to call in the directions indicated in the picture.
Capacitors.
Failed capacitors can be easily identified by convex caps or leaked electrolyte. Capacitors are replaced with similar ones. Replacement with capacitors slightly larger in capacity and voltage is allowed. If the capacitors in the standby power supply circuit fail, the power supply will turn on the nth time or refuse to turn on at all. A power supply with failed output filter capacitors will turn off under load or completely refuse to turn on and will go into protection.
Sometimes, dried out, degraded capacitors fail without any visible damage. In this case, you should first remove the capacitors and check their capacitance and internal resistance. If there is nothing to check the capacitance, we replace all capacitors with ones that are known to work.
Resistors.
The resistor value is determined by color marking. Resistors should only be replaced with similar ones, because A slight difference in resistance ratings can cause the resistor to overheat. And if it is a pull-up resistor, then the voltage in the circuit may go beyond the logic input, and the PWM will not generate a Power Good signal. If the resistor burns to charcoal and you don’t have a second power supply of the same type to check its value, then consider yourself out of luck. This is especially true for cheap power supplies, for which it is almost impossible to get circuit diagrams. Below is a table of resistor color coding:
Diodes and zener diodes.
They are checked by ringing in both directions. If they call in both directions like K.Z. or rupture, then they are not working properly. Burnt-out diodes should be replaced with similar or similar characteristics, paying attention to voltage, current and frequency of operation.
Transistors, diode assemblies.
It is most convenient to solder transistors and diode assemblies that are installed on the radiator together with the radiator. The “primary” contains power transistors, one is responsible for the standby voltage, and the others form the operating voltages of 12V and 3.3V. In the secondary on the radiator there are rectifier diodes for output voltages (Schottky diodes).
Checking the transistors consists of “vertebra” of the pn junctions; you should also check the resistance between the case and the radiator. Transistors should not be shorted to the radiator. Checking the diode bridge: If it is made as a separate assembly, you just need to carefully unsolder it and test the already separated circuit on the printed circuit board. If the rectifier is made of individual diodes, it is quite possible to check it without removing them all from the board. It is enough to test each of them for a short circuit in both directions, and unsolder only those suspected of being faulty. A working diode should have a resistance in the forward direction of about 600 Ohms and in the reverse direction - about 1.3 MOhms.
If all transistors and diode assemblies are in good working order, then do not rush to solder the radiators back, because they make it difficult to access other elements.
If the PWM is not visually damaged and does not heat up, then it is quite difficult to check it without an oscilloscope.
A simple way to check PWM is to check the control contacts and power contacts for breakdown.
To do this, we need a multimeter and a date sewn onto the PWM chip. PWM diagnostics should be carried out by first desoldering it. The test is carried out by ringing the following contacts relative to ground (GND): V3.3, V5, V12, VCC, OPP. If the resistance between one of these contacts and the ground is extremely small, up to tens of ohms, then the PWM should be replaced.
Method for checking the internal stabilizer: The essence of the method is to check the internal stabilizer of the microcircuit. This method is suitable for the tl494 model and its full analogues. When the power supply is disconnected from the network, you need to apply a constant voltage from +9 to +12 volts to the 12th leg of the microcircuit, while connecting the minus to the 7th leg, after which you need to measure the voltage on the 14th leg - it should be equals 5 volts. If the voltage is greatly deviated (±0.5 V), this indicates a malfunction of the internal stabilizer of the chip. It is better to buy this item new.
It is difficult to advise anything specific regarding the repair of the standby power supply - anything can burn out, but this is compensated for by the rather simple design of this part. It will be quite enough to surf the forums on this topic to find the cause of the malfunction and a method for eliminating it.
Emergency nutrition and POWER GOOD.
Now consider another situation: the fuse does not blow, all the elements mentioned above are working, but the device does not start.
Let's move away from the topic a little and remember how an ATX power supply works. In standby mode (this is where the computer is “turned off”), the power supply still works. It provides standby power to the motherboard so you can turn the computer on or off with a button, by a timer, or using any device. “Duty” is 5 volts, which are constantly (as long as the computer is connected to the electrical network) supplied to the motherboard. When you turn on the computer, the motherboard generates the PS_ON signal and starts the power supply. During the system startup process, all supply voltages are checked and the POWER GOOD signal is generated. If for some reason the voltage is very high or low, this signal is not generated and the system does not start. However, as mentioned above, in many NONAME power supplies there is no protection at all, which has a detrimental effect on the entire computer.
So, the first thing you need to do is check the presence of 5 volts on the +5VSB and PS_ON contacts. If there is no voltage on any of these contacts or it differs greatly from the nominal value, this indicates a malfunction either in the auxiliary converter circuit (if there is no +5 vsb), or a malfunction of the PWM controller or its wiring (PS_ON inoperability).
Group stabilization throttle (GS).
It fails due to overheating (when the fan stops) or due to miscalculations in the design of the power supply itself (example Microlab 420W). Burnt DGS can be easily identified by darkened, flaking, charred insulating varnish. A burnt-out DGS can be replaced with a similar one or a new one can be wound. If you decide to wind a new DGS, you should use a new ferrite ring, because Due to overheating, the old ring could have gone out of parameters.
Transformers.
To check transformers, they must first be desoldered. They are checked for short-circuited turns, broken windings, loss or change in the magnetic properties of the core.
To check a transformer for broken windings, a simple multimeter is enough; other transformer faults are much more difficult to determine and we will not consider them. Sometimes a broken transformer can be identified visually.
Experience shows that transformers rarely fail, so they should be checked last.
Ventilator prevention.
After successful repair, the fan should be prevented. To do this, the fan must be removed, disassembled, cleaned and lubricated.
The repaired power supply should be tested under load for a long time.
After reading this article, you will be able to easily repair the power supply yourself, thereby saving a couple of coins and saving yourself from going to a service center or store.
One of the important components of a modern personal computer is the power supply unit (PSU). If there is no power, the computer will not work.
On the other hand, if the power supply produces voltage beyond the permissible limits, this can cause failure of important and expensive components.
In such a unit, with the help of an inverter, the rectified mains voltage is converted into high-frequency alternating voltage, from which the low voltage flows necessary for computer operation are formed.
The ATX power supply circuit consists of 2 nodes - a mains voltage rectifier and one for the computer.
Mains rectifier is a bridge circuit with a capacitive filter. A constant voltage of 260 to 340 V is generated at the output of the device.
The main elements in the composition voltage converter are:
- an inverter that converts direct voltage into alternating voltage;
- high frequency, operating at a frequency of 60 kHz;
- low-voltage rectifiers with filters;
- control device.
In addition, the converter includes a standby voltage power supply, key control signal amplifiers, protection and stabilization circuits, as well as other elements.
The inverter includes two power transistors operating in switching mode and controlled using signals with a frequency of 60 kHz coming from a control circuit implemented on the TL494 chip.
A pulse transformer is used as the inverter load, from which the voltages +3.3 V, +5 V, +12 V, -5 V, -12 V are removed, rectified and filtered.
Main causes of malfunctions
The causes of malfunctions in the power supply can be:
- surges and fluctuations in supply voltage;
- poor quality manufacturing of the product;
- overheating due to poor fan performance.
Malfunctions usually lead to the fact that the computer system unit stops starting or turns off after a short period of operation. In other cases, despite the operation of other units, the motherboard does not start.
Before starting repairs, you need to finally make sure that it is the power supply that is faulty. In this case, first you need check the functionality of the network cable and power switch. After making sure that they are in good condition, you can disconnect the cables and remove them from the system unit case.
Before you turn on the power supply autonomously again, you need to connect the load to it. To do this, you will need resistors that are connected to the corresponding terminals.
In this case, the value of the resistance of the load resistors must be selected so that currents flow through the circuits, the values of which correspond to the nominal values.
The power dissipation must correspond to the rated voltages and currents.
First you need to check motherboard influence. To do this, you need to close two contacts on the power supply connector. On a 20-pin connector, these will be pin 14 (the wire that carries the Power On signal) and pin 15 (the wire that corresponds to the GND - Ground pin). For a 24-pin connector, these will be pins 16 and 17, respectively.
The serviceability of the power supply can be assessed by the rotation of its fan. If the fan rotates, the power supply is working.
Next you need to check voltage correspondence at the unit connector their nominal values. It should be taken into account that, in accordance with the documentation for the ATX power supply, the deviation of voltage values for the -12V power circuit is allowed within ± 10%, and for other power circuits ± 5%. If these conditions are not met, you must proceed to repair the power supply.
ATX computer power supply repair
After removing the cover from the power supply, you must immediately clean all dust from it using a vacuum cleaner. It is because of dust that radio components often fail, since dust, covering the part with a thick layer, causes overheating of such parts.
The next step in troubleshooting is a thorough inspection of all elements. Particular attention should be paid to electrolytic capacitors. The reason for their breakdown may be severe temperature conditions. Faulty capacitors usually swell and leak electrolyte.
Such parts must be replaced with new ones with the same ratings and operating voltages. Sometimes the appearance of the capacitor does not indicate its malfunction. If, based on indirect signs, there is a suspicion of poor performance, then it is possible. But for this it needs to be removed from the circuit.
Deterioration in thermal conditions inside the unit may be due to poor performance of the cooler. To improve performance, it must be cleaned of dust and the bearings lubricated with machine oil.
A faulty power supply can also be caused by faulty low-voltage diodes. To check, you need to measure the resistance of the forward and reverse transitions of the elements using a multimeter. To replace faulty diodes, you must use the same Schottky diodes.
The next malfunction that can be determined visually is the formation of ring cracks that break the contacts. To detect such defects, you need to carefully examine the printed circuit board. To eliminate such defects, it is necessary to carefully solder the places where cracks form (for this you need to know).
Resistors, fuses, inductors, and transformers are inspected in the same way.
If a fuse is blown, it can be replaced with another one or repaired. The power supply uses a special element that has leads for soldering. To repair a faulty fuse, it is removed from the circuit. Then the metal cups are heated and removed from the glass tube. Then select a wire of the desired diameter.
The wire diameter required for a given current can be found in the tables. For the 5A ATX fuse used in the circuit of the ATX power supply, the diameter of the copper wire will be 0.175 mm. Then the wire is inserted into the holes of the fuse cups and fixed by soldering. The repaired fuse can be soldered into the circuit.
The most common malfunctions of a computer power supply are discussed above.
Detecting and repairing more complex faults requires good technical training and more sophisticated measuring instruments, such as an oscilloscope.
In addition, elements that need to be replaced are often in short supply and are quite expensive. Therefore, in case of a complex malfunction, you should always compare the costs of repairs and the costs of purchasing a new power supply. It often happens that it is more profitable to purchase a new one.
conclusions:
- One of the most important elements of a PC is the power supply; if it fails, the computer stops working.
- The computer power supply is a rather complex device, but in some cases you can repair it yourself.
Problems with the power supply can easily arise precisely because it is a separate device, like other components. With its own design and a fairly extensive set of components inside. The power supply can also fail and malfunction. It also contains those already familiar to us (from previous articles). They can “swell”, “boil” and otherwise complicate our lives in exactly the same way.
Here, by the way, is a photo of the power system capacitor, which was the cause of the problem with the power supply.
Do you see this “rust” (oxide) on it? This is leaked electrolyte. In this case, the unsuitable capacitors are replaced (resoldered with working ones of the appropriate capacity, while maintaining the correct capacitors).
Let's look at the possible options for what could cause our power supply to fail and what could be the consequences for the rest of the “stuffing” of the system unit? Problems with the power supply are often associated with the fact that it completely fails due to voltage surges in the electrical network or high-frequency power supply noise. In this case, the input circuits of the device (inverter or filter) are often “under the gun.”
But if you have a cheap power supply (made on the honest Chinese word), there are situations when the input voltage surge passes through the filter and instantly ends up at the output of the power supply and burns out the stabilizers at the power input of the motherboard itself. Here, as you understand, the matter will no longer be limited to simply replacing the power supply unit. In such a situation, as a rule, power impulses pass through all components of the motherboard, some of which can easily fail.
Cheap units often do not contain the required number of electrical filters in their design. Filters are replaced with jumpers, which reduces the cost of production of the final product, but creates additional problems with the power supply later. For example, look at this example:
What do we see here? At the bottom (circled in red) two jumpers are soldered in place of filter chokes (or fuses), and above them there is an empty seat for capacitors of the same filtering circuit. The manufacturer saved even on such a cheap but important element as an insulating plastic gasket that protects the high-voltage part of the electrical circuit from accidental contact with the housing casing.
Note: You can see two chokes at the top of the photo; these are ferrite rings with turns of copper wire wound on them. The inductor has a high resistance to alternating current and a low resistance to direct current and serves specifically to filter (suppress) the alternating current component in an electrical circuit.
In the photo below, pay attention to the darkening inside the power supply, marked in red. In the upper part of the image we see burnt-out resistance resistors, which serve to equalize (lower) the voltage inside the power supply. Due to their “breakdown” and, as a consequence, the increased current strength, the device began to operate in overload mode, which, in turn, led to the burnout of the area under the capacitors (lower area) and their swelling.
When operating in overload mode, the power supply may emit a high-frequency “whistle,” which should serve as a signal for prompt action on our part. If we leave everything to chance, then soon we may see nothing more when we turn on the computer.
Various voltage surges can also lead to failure of elements of the power supply such as diode assemblies (diode bridge), which acts as a voltage rectifier. Typically these are four diodes (assembly), located in one housing and used for rectification (conversion) into a pulsating constant.
Problems with the power supply can also begin due to the fact that the power supply does not have time to stabilize the electrical voltage inside the system unit. In a high-quality product, electronic stabilization units operate quite quickly, but in cheap and low-quality products, as you understand, with this everything is the opposite.
In the photo above there is a “broken” PWM controller ( PWM- pulse-width modulator or in English: pulse-width modulation - PWM), which performs the functions of a regulator and voltage stabilizer in the power supply. A similar controller also controls the computer's motherboard. PWM also provides protection against exceeding the positive and negative output voltages of the power supply unit and generates the “ ” signal.
Pay attention to the photo below:
Do you see how the cap was blown off the capacitor? :) At the same time, the liquid electrolyte filling it splashed all over the power supply and, while I took the computer for repairs, the electrolyte managed to stink the whole room :)
A similar problem with the power supply occurred as a result of a strong voltage surge in the electrical network, as a result of which, in fact, the power supply itself, the transformer of the active speaker system, and the motherboard of the printer connected to this computer failed. Moreover, on the board itself the varistor on 600 ! Volt.
There is also this problem: the power supply turns on itself after connecting the power cable. All the fans in the system unit spin, but the computer does not turn on. The cause of such a breakdown, in most cases, is a malfunction of the standby voltage stabilizer of the power supply, which forms the “standby voltage” (standby voltage +5V). Without receiving it at startup, the system simply cannot correctly pass the initial stage of self-testing, which is why the main voltages are not supplied to the computer components and it does not start.
On my tester's display it looks like this:
Moreover, the tester emits a warning signal, and the values of the VSB (standby voltage) indicator dynamically change from 3.9 to 4.8V.
We looked at how to check the power supply yourself on our website.
Let's continue! Voltage stabilization problems are especially noticeable in a situation where the power consumed by one or another computer component (often a processor) can change abruptly (with a frequency of up to a megahertz). If the power supply does not have time to “catch up” with the sharply falling voltage, then interference occurs that can distort the data being transmitted inside the computer at that moment. Naturally, the computer begins to “glitch”, various unpleasant things happen, in the form of spontaneous reboots, the appearance of “blue screens” (BSOD), the appearance of bad blocks on the hard drive, etc.
And this is the other side of when they try to equip the power supply to the maximum:
Due to such a high density of components in a limited space, we are faced with another problem of the power supply - its overheating. Overheating for this computer node is just as dangerous as, for example, .
In the photo above we can see that due to lack of space, the filter winding was taken out separately (in the photo on the right) and attached from the inside to the power supply cover. There was also not enough space for the fan speed control board, which was screwed directly to one of the radiators. As a result, the entire structure heats up terribly and is unlikely to last long in such operating conditions.
Problems with the power supply can also arise as a result of its natural “aging”, which is much more intense than all other computer components. After a year of operation, many power supplies lose 10-20% of their initial power. In case of operation in extreme conditions (prolonged overheating, maximum load), this figure can reach up to 50%.
They especially suffer from unstable or low voltage. To spin the spindle and maintain speed, the controller must supply constant power to its motor. If the voltage drops or fluctuates, then solving such a problem becomes problematic and hence additional problems.
In my practice, there was a case when, after turning on the computer’s power button, I heard a loud bang and a burning smell (I thought: “the power supply has failed, needs to be replaced”), but even after replacing it with a known good one, the computer did not turn on. As a result of subsequent testing, it turned out that the power supply protection circuit did not work and almost everything inside burned out (even the keyboard connected to the PC at that time failed!). Only the external one and the mouse remained “alive”; all the other “stuffing” had to be simply thrown away!
If there is a sudden surge in voltage in the electrical network, the fuse located inside the power supply may fail. Moreover, the unit itself may be fully operational and the problem lies precisely in the failed fuse, which is intended to protect the expensive elements located behind it. Always keep this moment in your head!
To check this, simply switch to the test mode and touch the fuse probes on both sides (the location of the probes does not matter). The tester should emit a beep; if there is no signal, carefully inspect the element visually (most likely, the wire running inside it is broken).
Typically, power supplies are equipped with fuses rated up to five amperes (5A). The markings can be seen on the element body itself. It is also often written on the printed circuit board of the power supply near the fuse installation location or on its back side. So repairing the power supply, with some luck, can come down to a banal replacement of a small part!
We just go to the nearest specialized store (or radio market) and buy a fuse of the required rating. Using a soldering iron, the faulty element (first completely remove the power supply board by unscrewing the four screws) and install a new one in its place. If nothing else has burned out, then the whole “repair” may end there. Agree, it’s worth spending a little time than paying a technician (even worse, throwing away) a fully working computer unit :)
What can be recommended to avoid problems with the computer power supply? In fact, the only worthwhile recommendation here is to use only high-quality power supplies from reputable well-known manufacturers. Of course, such a unit will cost more, but this is your payment for the safety and reliability of the entire system. Don't neglect this!
To the trustworthy" branded"computer power supply manufacturers relate: Delta, FSP, Hiper, 3R, Topower, Chieftec, HEC, Thermaltake, ASUS, PowerMan Pro, AcBel, ZIPPY (Emacs), Enermax, Zalman, Enlight, Epsilon. It is highly advisable to take a power supply with at least 20-30% excess power reserve. You don't plan to operate it under maximum load, do you?
A general recommendation for preventing power supply failures may be advice not to keep the system unit on the floor. Practice shows: the lower it is located, the more dust gets into it, and conductive dust accumulating on electrical contacts is the enemy of any electronics.
It is also highly advisable to use (UPS) or at least a high-quality surge protector. For example, the “Most Tandem THV” surge protector:
Such filters have built-in protection circuits against high-frequency interference, as well as against overvoltage in the electrical network. For example, when instead of the required 220 V, our utility workers supply 260 V or more to your outlet. This filter, upon reaching a threshold of 252 V, simply turns off, saving the expensive equipment located behind it.
So, what signs can be identified regarding power supply problems? First and the main one, which brings to mind primarily the power supply - the computer simply does not turn on. After pressing the start button, literally nothing happens (fans don't spin, lights don't light up). Another sign- not so clearly indicating that the problem is in the power supply: the system spontaneously reboots or freezes.
How can we make sure that our problems are with the power supply? First of all, replace it with one that is known to work. If after this the computer works stably, then the problem is localized correctly :)
There is one little trick that will help you start the power supply without connecting it to the motherboard. Literally, to start it, you only need the unit itself, a 220-volt cable and a paper clip.
Let's get started. We remove it from the case, place it on the table and, using a bent paper clip, close the 14th and 16th contacts on its connector. As shown in the photo below.
The green and black wires must be shorted. But don’t worry, even if you accidentally close the wrong contacts, nothing bad will happen (the power supply will not burn out, it just won’t start). After we have fixed the paperclip in this position, we connect the power cable to the device and plug it into the outlet. If everything is done correctly, the fan on the unit will begin to rotate.
It is clear that in this way you can only successfully test the power supply for “works” - “doesn’t work”, but if the problems are caused, for example, by swollen capacitors inside, then such a test will not show us how stable the device functions, even here without an oscilloscope (for detecting voltage “ripples”) in the power supply is no longer necessary.
Problems with the power supply can manifest themselves in different ways. For example: the company bought us a good computer (high-quality components, a 400-watt power supply from Chieftec). Literally a month later it comes to us for repairs. Diagnosis - not included.
We disassembled the power supply and see that one of the power elements has slightly deviated to the side and is touching the inside of the protective casing. The result is a short circuit to the housing and failure of the entire device.
Another example from practice. Although it is not directly related to power supply problems, it will show you another nuance of computer diagnostics.
Another case in our IT department: they brought us a computer that would not start. Standard scheme - change the power supply. No changes. We substitute other (obviously working) components - the same situation. We reset the BIOS and do some of the things we described in the previous article "". To no avail!
We start thinking about a non-working motherboard. And then someone comes up with the idea to check if everything is ok with the power button of the computer itself? We remove the front panel of the computer case and see that one of the two contact wires leading to the connector on the motherboard has come off at the base of the button itself.
Naturally, we soldered the wire in place, but firstly: it will be useful for you to know that the cause of the apparent problem with the power supply may be precisely this. And secondly: there is another way to start the motherboard without using the start button on the front panel.
To do this, we need to find two pins on the motherboard that are responsible for starting the computer (they are usually labeled “PWR”, “POWER”, “POWER ON” or “POWER SW”) and short them directly using a flat-head screwdriver.
Hold the screwdriver like this for a few seconds. The computer should start (if it is working). Don't be afraid if you short out the wrong pins. You can (in the absence of clear labeling) try them all. The motherboard will not burn out and nothing bad will happen. I just want you to know about this opportunity and apply this knowledge at the right time and in the right situation.
To summarize all of the above: problems with the power supply can be solved in two ways:
- 1 - replacing components in it itself
- 2 - buying a new one
Here, by the way, is how people get out of the situation if they have problems with the power supply if they have a “desktop” type case (narrow horizontal).
As you can see, the original power supply burned out, and the standard ATX simply did not fit, but our Slavic ingenuity and wide adhesive tape came to the rescue! :)
Therefore, always be careful when testing, do not make hasty conclusions. Remember what one well-known character said about this: “Only cats will be born quickly!” And finally: do not forget that problems with the power supply can begin from the lack of regular cleaning of it (and the entire system unit inside) from dust. Dust accumulated on the power supply fan can eventually lead to it jamming and stopping completely, and this is a direct road to overheating of the device, “with all that it entails.”
Let's expand our article a little more with photographs kindly provided by one of our website visitors. Special thanks to him for this! :) The photo below will depict the extreme stage of what can (God forbid) happen to your computer if you do not periodically do preventive maintenance and do not remove the dust accumulated in it.
So - a parade of our photos! Photo one: Power supply from the back.
Cleaning can be carried out using an old Soviet-style vacuum cleaner set to for blowing or - using a can of compressed air. Of course, in such “clinical” cases of clogging, it will be necessary to resort to other, non-standard means. After wiping with alcohol, be sure to let the computer dry thoroughly. Good luck to you! :)
To learn how to repair this computer unit yourself if there are problems with the power supply, watch the video below. The entire process is clearly shown: from diagnosing a breakdown to replacing faulty power supply components.
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