Computer power supply does not work

The computer doesn’t start the power supply is healthy. The processor is down

Even the most careful user is faced with a situation where his computer suddenly stops booting. This can be due to a variety of reasons. hardware, software or due to the combined effect of both. How they can be detected? What are the available ways to fix the damages that prevent the PC from booting?

Strictly speaking, a situation in which the computer does not turn on at all, that is, when there is no reaction to pressing the power button, is rare. It is caused by a countless number of reasons, for example, simply by the fact that the apartment is off.

Many users understand the state when the computer doesn’t turn on at all as the absence of images on the screen, while the system unit is habitually buzzing and the lights on it are lit. There is another interpretation of the problem. the image is, but does not boot Windows. In this sense, the user identifies this state of affairs with the fact that the computer does not turn on at all, since the result is the same: one cannot work on a PC. We will consider several scenarios, taking into account different perspectives of users on the essence of the problem in question.

The situation when the computer at all, as we noted above. quite rare. Most often those or other mechanisms on the system unit still begin to work, but for a variety of reasons further boot PC becomes impossible. The architecture of modern PCs has a mechanism that assumes that in case of such failures the I/O system. BIOS. signals about them through sounds similar to squeaking. They can be heard in the speakers or in a small speaker built into the motherboard. Let’s look at their features.

Computer power supply. How to determine the fault?

The cases of power supply unit failure in the computer are not uncommon. Below are the possible causes of malfunction of computer power supplies and how to check the power supply for performance.

Poor workmanship, especially for cheap power supplies and system units;

Unfortunate design and circuitry solutions;

The use of low-quality components in the manufacture;

Overheating of elements due to bad location of the system unit, contamination of the power supply unit, cooling fan stoppage.

What are the “symptoms” of power supply unit failure in the computer?

Most often it is a complete absence of life signs of the system unit, i.e. nothing is buzzing, indication LEDs are not lit, there are no beeps.

In some cases the motherboard does not start. The fans may be spinning, the LEDs may be on, and the drives and hard drive may be making noises, but nothing appears on the monitor screen.

Sometimes the system unit starts to show signs of life for a few seconds when turned on, and then immediately shuts down due to the overload protection of the power supply.

To finally verify the malfunction of the power supply it is necessary to open the right lid of the system unit, when viewed from the back. Remove the main plug of the main power supply connector, which has 20 or 24 pins, from the socket of the motherboard, and short-circuit the contacts with the green (sometimes gray) and the nearest black wire. If this starts the power supply, then you are most likely blaming the motherboard.

You can tell if the power supply is running by the rotation of the power supply fan if it’s OK and the clicks of the drives, but to be sure it’s better to check the voltages on the connector. Between the black and red wire pins. 5v, between black and yellow. 12v, between black and pink. 3.3v; between black and purple. 5v standby voltage. Minus on the black and plus on the colored. To be sure that the power supply is working, just measure one of the voltages, aside from the 5 volt on the purple wire.

Sometimes users start looking for a fuse. Do not look, there are none outside. There is one inside, but to change it in most cases is not only useless, but also dangerous and harmful, because it can lead to even more problems.

If you find that the power supply is defective, in most cases it is better to replace it, but it can also be repaired if it is economically feasible.

When buying a new power supply, you must first consider the power, which should not be less than the former. You should also pay attention to the output connectors, so that it is possible to connect all the devices of the system unit, although in necessary cases connection problems can be solved with adapters. On how to choose a power supply of the right quality you can read here.

Do I have to repair the power supply myself?? If you do not have at least rudimentary knowledge and skills in electronics, definitely not. First of all you probably can’t do it, and secondly it is dangerous to your life and health if you don’t follow the safety rules.

For those who do decide to do power supply repair, you can read my personal experience and thoughts on the subject here.

The symptoms of a faulty power supply

often than not, it is simply impossible to tell if the power supply is faulty. However, there are several symptoms that suggest a possible problem.

• A strange noise coming from the back of the computer case, where the cord is. Power supply beeping and not turning on.
• Nothing happens when the computer is turned on. Sometimes this can coincide with a blinking LED on the front of the computer or the indicator on the back of the power supply (if available).
• The power supply turns on and immediately turns off. It may also be caused by a problem with the power supply. It can also indicate a problem with the motherboard.
• The computer works for a while, but when you start a game or other program, it shuts down without warning. You may also get a blue screen of death.

If we are talking about gaming, you should know that modern graphics cards consume a lot of power and amps. So, you should make sure that the power supply is enough to run the equipment inside your computer, especially the graphics card.

The “staple” method

There is a simple method among users, how to check the power supply with a paper clip. Our resource will not stand aside and tell you what this method is, especially since practically the same has been discussed in the section about using a multimeter. This is the easiest, you can say, home method, which can not show the quality of the voltage source, but fairly reliably will give an indication of whether it turns on or off.

• Disconnect PC from the mains.
• Open the case and unplug the connector from the motherboard.
• Using a paper clip make a U-shaped jumper to short circuit the green wire of the plug to the black wire of the power supply.
• Plug the PSU into a 220V outlet.

If the fan starts working the PSU is theoretically in working condition, if not. definitely go for repair.

Warning signs of power supply malfunction

The reason to think about the necessity of BP repair is the situation when the computer does not turn on the first time. Shutting down the PC at the stage of loading the operating system is also a sign of power supply failure. Such a problem indicates overheating of the PSU, which results in a forced shutdown of the computer.

Repair of a computer also is necessary if it switches off for no reason at any time. Another “symptom” of power supply malfunctioning is a strong heating. This “symptom” indicates possible problems with the cooler. Another reason to ask for professional help is the “blue screen of death” or the smell of burning when you start your PC.

Power Supply Trouble

Before we get into power supply problems, be sure to read the two articles that will give you some background information on what a power supply is and how it connects to the motherboard (article. “Connecting a Power Supply”).

Problems with your power supply can easily arise precisely because it. is as much a separate piece of hardware as the other components. With its design and quite a wide range of components inside. The power supply can also fail and malfunction. It also contains electrolytic capacitors, which we are already familiar with (from previous articles). They can also “blow up”, “boil” and otherwise make our lives difficult.

Here, by the way, is a photo of the power supply capacitor that was the cause of the problem with the power supply.

Do you see this “rust” (oxide) on it?? It is. leaked electrolyte. In that case unsuitable capacitors are replaced (soldered over with working capacitors of the corresponding capacity, observing the correct polarity when soldering.

Let’s look at the possible options from what our power supply unit can fail and what consequences this may have for the rest of the “stuffing” of the system unit? Problems with the power supply are often due to the fact that it fails completely when there are surges in the mains or. high frequency interference of the power supply. In this case, often under the “target” are the input circuits of the device (inverter or filter).

But if you have a cheap power supply (made on the word of honor), there are situations when the input voltage surge passes the filter and instantly appears on the output of the power supply and burns out the stabilizers on the power input of the motherboard itself. Here you understand that just replacing the power supply unit is not enough. In such a situation, as a rule, power pulses go through all the motherboard components, some of which can easily fail.

Cheap units often do not contain the necessary number of electrical filters. The filters are replaced by jumpers, which makes the final product cheaper, but creates additional problems with the power supply later on. For example, look at this sample:

What we see here? At the bottom (circled in red) two jumpers are soldered in place of the filter chokes (or. fuses), and above them. empty seat for capacitors of the same filtering scheme. The manufacturer has spared even such a small but important element, as an insulating plastic gasket that protects the high-voltage part of the circuit from accidental contact with the case casing.

Note: the two reactors you can see at the top of the picture are. ferrite rings with coils of copper wire wound on them. The choke has a high AC resistance and a low. constant and serves precisely to filter (suppress) the alternating component of the current in the circuit.

In the photo below notice the darkening inside the PSU which is marked in red. In the upper part of the image we see the burned-out resistors, which serve to equalize (lower) the voltage inside the PSU. Because of their “breakdown” and as a consequence of the. The power supply was overloaded by the increased current and this caused the capacitors (lower area) to burn out and swell.

When operating in overload mode, the power supply may emit a high-frequency “whistle”, which should be a signal for prompt action on our part. If everything is left on its own, then in a short time we can see a black screen and nothing else when turning on the computer.

Various voltage surges can also lead to failure of power supply elements, such as diode assemblies (diode bridge), which performs the function of a voltage rectifier. This is usually four diodes (assembly), located in one housing and serves to rectify (convert) alternating current into a pulsating direct current.

Problems with the power supply can also start because the PSU does not have time to stabilize the electric voltage inside the system unit. The good quality product has electronic control units that work fast enough, and the cheap and low-quality ones, as you know, are all about. reverse.

In the photo above. A “punctured” shim controller (PWM. pulse-width modulator, or in English: pulse-width modulation. PWM), which acts as a regulator and voltage regulator in the power supply. Similar controller also controls the power phases on your computer‘s motherboard. PWM also provides protection against exceeding the positive and negative output voltages of the PSU and generates a “Power Good” signal.

See how the capacitor blew its “roof”? 🙂 The liquid electrolyte that filled it splashed all over the power supply and by the time I had taken the computer for repair, the electrolyte had managed to stink up the whole room 🙂

Such a problem with the power supply unit has occurred as a result of a strong surge in the mains voltage, as a result of which the power supply itself, the transformer of the active speaker system, and the motherboard of the printer connected to this computer have all failed. And on the board itself is soaked and burnt varistor to 600 ! Volt.

There is also the following problem: The power supply turns on by itself after connecting the power cable. All the fans in the system unit at the same time spinning, but the computer does not turn on. The cause of such failure, in most cases, is a failure of the standby voltage regulator of the power supply, which forms the “standby” (standby voltage 5V). Without getting it at startup, the system simply can’t complete the initial self-test correctly, which is why. The mains voltage is not supplied to the computer components and the computer does not start.

Load equivalent

The power supply, when started “by wire”, started. Do not rush to install it in the computer. Let’s try to test the PSU with a load equivalent. Such resistors are taken:

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

The main thing here is to make a circuit 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 “12V” line for trimmer, 3-ohm. to “5V”. To connect to the PSU, use a Molex connector (yellow wire is 12V):

Note: when creating an “equivalent”, consider the power that falls on each resistor (it must not exceed the value for which it is designed). Knowing the voltage across the resistor, the power is found by the law: Voltage squared / resistance. Example: 4 20 ohm resistors. “in parallel”, each with 7.5 watts of power (to test the “12 volt” line). You can use even halogen bulbs for 12V (let’s say: two 10 Watt bulbs in parallel). So, after we have connected the equivalent of the load to the Molex socket, we try to switch on the power supply unit (“light green”/”black”, ATX socket). 220 V power cord, also must be “normal”. If this happens, wait for 10 seconds. Doesn’t the unit go to protection? The fan should rotate and all voltages should be in the proper range (no more than 5-6% deviation is allowed). Basically, in this “sparing” for him mode, any PSU should work as long as you like. You can make a more powerful “equivalent”. That is, resistance in ohms is even lower. The main thing is not to “overdo it” (for each PSU, the maximum amperage is specified):

The current through the load is equal to the voltage divided by its resistance (in ohms). Well, this. you already know When testing, the “load” will be included only in two lines (“plus 5”, “plus 12”). This is, in general, enough. The other voltages (“minuses”), can be measured with a voltmeter (on a 24-pin plug). Note: If you want to “test” the trimmer line “12” with a current strength greater than 6A. do not use Molex connectors! A 4 pin 12 volt CPU power connector can hold up to 10 amps. If necessary, the load is “split” between the two connectors (CPU, “molex”). Note 2: When making any connections, use wire of sufficient cross-section (at 1mm²) 10A). The equivalent of the load, will produce heat (thermal power equal to electrical power). Take care of cooling (air supply). During testing, for the first 2-3 minutes, it is better to watch whether one of the resistors overheats.

Why a computer power supply may not work?

• Unstable mains voltage
• Sudden power ups and downs
• Wear and tear and degradation with age
• Poor workmanship or manufacturing defects
• Dust accumulation inside the case with cooling deterioration
• Electrical conduction of dust due to increased humidity
• Attempts to reduce the noise of the PSU cooler (muffle, lower the voltage)
• Connecting powerful equipment with PSU overload

With each surge it becomes more and more painful to endure abnormal situations. Over time the PSU will overheat and go into “protection. Someday it will stop failing and take some of the PC components out of service.

Plan the timely replacement of the computer power supply unit, when you upgrade to a more powerful device or when the general computing load increases. avoid the risk of increased wear and tear of such an important component of the system.

Stable power supply and connection at least through the filter will guarantee long life of the power supply and absence of reasons why it can not work and break your computer. When managing the IT-infrastructure of the office always consider this point and include uninterruptible power supplies in the estimates on time.

Do not save on a computer power supply and equipment to connect to the mains. You will win on the cost of service and provide a minimum guarantee of stable operation of the enterprise.

ZEL-Services Company

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