How to find out if the power supply is burned out. Diagnostics of a computer power supply

A PC may not turn on for many reasons, and one of them is a faulty power supply. In this article we will show you how to diagnose its malfunctions and what solutions exist.
A computer power supply (sometimes we will use its abbreviated name, PSU) is designed to supply device nodes with constant electric shock. The principle of operation of the secondary power supply is to convert the mains voltage to the required value. The power supply also stabilizes and protects the computer from voltage interference.

The following follows from this: the power supply, an intermediate link between the mains voltage and the hardware and software computer, it is very important in its operation, and therefore any malfunction can damage the PC.

Causes and symptoms of power supply failure

1st reason: Frequently repeated surges in voltage in the electrical network, or when it goes beyond the permissible values ​​within which the power supply can operate.

2nd reason: The power supply components are made of low-quality materials (this is especially true for cheap Chinese devices).

The following four symptoms indicate faulty power supplies:

1. If you press the system unit's power button, nothing will happen. You will not hear sound, see lights or rotate cooling fans.
2. The computer periodically turns on, does not turn on, or reboots on its own from time to time.
3. The OS loads, but after a while it turns off, although there is sound and light, and the fans are spinning.
4. A special utility or BIOS settings show that the temperature in the system unit and power supply is increased. This can be determined without opening the case. In this case, the computer often reboots, the OS slows down, and the coolers spin too quickly. An excessive increase in temperature threatens failures of all PC components: video card, motherboard, hard drives, etc.

1. Using this method, we will check the most basic thing - whether voltage is supplied to the power supply.
2. Using this method we will check the output voltage to see if it is within the required range. stable operation range.
3. This method will allow us to visually inspect the power supply and see a malfunction, for example, swollen capacitors, accumulated dust, or a failed fan.

Checking the power supply voltage

Before completing this step and moving on to the next, take pictures on your phone/tablet so that you can properly connect power to the motherboard, optical drive, hard drive and other computer components. And only after that, disconnect everything from the power supply.

Fourth step Find the power connector in the system unit, which consists of 20 or 24 wires, coiled in the form of a bundle. These wires connect the motherboard and power supply of the computer.

Step seven At this stage, the health of the power supply fan is diagnosed. If the power supply is operational, then the voltage will start the fan (you will see the rotation of the coolers).

If they do not rotate, the paperclip that contacts the two connectors (black and green wires) may have moved and is not in place.

This diagnostic, we repeat, is the most unreliable and is not a guarantee of the performance of the power supply. It only makes it possible to find out whether the device turns on. Let's move on...

Checking the correct operation of the power supply

Fifth step To obtain correct output voltage values, they should only be measured when the power supply is under load. PSU supplies hard drives, fans, drives, motherboard, working under load. Otherwise, our diagnosis will be incorrect: it will show a high error in values.

Step six Apply power to the device, first turning on the button if it was turned off when performing the first step of the instructions.

Step Seven Here we measure the output voltage of the power supply on the wires found in the third step using a voltmeter. Pink and black wires have the lowest voltage value - 3.3 volts, red and black - 5V, and yellow and black - 12V.

All listed values ​​may deviate slightly, by 5%, in one direction or another. These are the acceptable limits:

• 3.3 volts - 3.13 - 3.46;
• 5 volts - 4.74 - 5.24;
• 12 volts - 11.3 - 12.5.

Visual inspection of the power supply

If you find all this, do the following:

1. Vacuum the power supply thoroughly and gently.
2. Lubricate or replace the fan.
3. Resolder faulty capacitors.

Since the trend now is to reduce the cost of production as much as possible, low-quality goods quickly reach the repairman’s door. When buying a computer (especially the first one), many choose the “most beautiful of the cheap” case with a built-in power supply - and many do not even know that such a device is there. This is a “hidden device” on which sellers save a lot. But the buyer will pay for the problems.

About the main thing

Today we will touch on the topic of repairing computer power supplies, or rather their initial diagnostics. If there is a problematic or suspicious power supply, then it is advisable to carry out diagnostics separately from the computer (just in case). And this unit will help us with this:

The block consists of loads on lines +3.3, +5, +12, +5vSB (standby power). It is needed to simulate a computer load and measure output voltages. Since without load the power supply can show normal results, but under load many problems can appear.

Preparatory theory

We will load with anything (whatever you find on the farm) - powerful resistors and lamps.

I had 2 car lamps 12V 55W/50W lying around - two spirals (high/low beam). One spiral is damaged - we will use the second one. There is no need to buy them - ask your fellow motorists.

Of course, incandescent lamps have very low resistance when cold - and will create heavy load on short time- and the cheap Chinese may not be able to withstand this and not start. But the advantage of lamps is accessibility. If I can get powerful resistors, I’ll install them instead of lamps.

Resistors can be looked for in old devices (tube TVs, radios) with resistance (1-15 Ohms).

You can also use a nichrome spiral. Use a multimeter to select the length with the required resistance.

We will not load it to full capacity, otherwise we will end up with 450W in the air as a heater. But 150 watts will be fine. If practice shows that more is needed, we’ll add it. By the way, this is the approximate consumption of an office PC. And the extra watts are calculated along the +3.3 and +5 volt lines - which are little used - approximately 5 amperes each. And the label boldly says 30A, which is 200 watts that the PC cannot use. And the +12 line is often not enough.

For the load I have in stock:

3pcs resistors 8.2ohm 7.5w

3pcs resistors 5.1ohm 7.5w

Resistor 8.2ohm 5w

12v lamps: 55w, 55w, 45w, 21w

For calculations we will use formulas in a very convenient form (I have it hanging on the wall - I recommend it to everyone)

So let's choose the load:

Line +3.3V– used mainly for food RAM– approximately 5 watts per bar. We will load at ~10 watts. We calculate required resistance resistor

R=V 2 /P=3.3 2 /10=1.1 Ohm we don’t have these, the minimum is 5.1 ohm. We calculate how much it will consume P=V 2 /R=3.3 2 /5.1=2.1W - not enough, you can put 3 in parallel - but we get only 6W for three - not the best good use such powerful resistors (by 25%) - and they will take up a lot of space. I’m not installing anything yet - I’ll look for 1-2 Ohms.

Line +5V– little used these days. I looked at the tests - on average he eats 5A.

We will load at ~20 watts. R=V 2 /P=5 2 /20=1.25 Ohm - also a low resistance, BUT we already have 5 volts - and even squared - we get a much larger load on the same 5 ohm resistors. P=V 2 /R=5 2 /5.1=4.9W – put 3 and we will have 15 W. You can add 2-3 on the 8th (they will consume 3W), or you can leave it like that.

Line +12V- the most popular. There is a processor, a video card, and some little gadgets (coolers, drives, DVDs).

We will load at as much as 155 watts. But separately: 55 per power connector motherboard, and 55 (+45 via a switch) to the processor power connector. We will use car lamps.

Line +5 VSB- emergency meals.

We will load at ~5 watts. There is an 8.2 ohm 5w resistor, let's try it.

Calculate powerP=V 2 /R=5 2 /8.2= 3 W Well, that's enough.

Line -12V– here we connect the fan.

Chips

We will also add a small-sized 220V 60W lamp to the housing in the 220V network break. During repairs, it is often used to identify short circuits (after replacing some parts).

Assembling the device

Ironically, we will also use the case from a computer power supply (non-working).

We unsolder the sockets for the power connector of the motherboard and processor from the faulty motherboard. We solder the cables to them. It is advisable to choose colors as for the connectors from the power supply.

We are preparing resistors, lamps, ice indicators, switches and a connector for measurements.

We connect everything according to the scheme... more precisely, according to the VIP scheme :)

We twist, drill, solder - and you're done:

Everything should be clear by appearance.

Bonus

Initially I didn’t plan it, but for convenience I decided to add a voltmeter. This will make the device more autonomous - although during repairs the multimeter is still somewhere nearby. I looked at cheap 2-wire ones (which are powered by the measured voltage) - 3-30 V - just the right range. Simply by connecting to the measurement connector. But I had 4.5-30 V and I decided to install a 3-wire 0-100 V - and power it from charging mobile phone(also added to the case). So it will be independent and show voltages from zero.

This voltmeter can also be used to measure external sources(battery or something else...) – by connecting it to the measuring connector (if the multimeter has disappeared somewhere).

A few words about switches.

S1 – select the connection method: through a 220V lamp (Off) or directly (On). At the first start and after each soldering, we check it through a lamp.

S2 – 220V power is supplied to the power supply. The standby power should start working and the LED +5VSB should light up.

S3 – PS-ON is shorted to ground, the power supply should start.

S4 – 50W addition on the processor line. (50 is already there, there will be a 100W load)

SW1 – Use the switch to select the power line and check one by one if all voltages are normal.

Since our measurements are shown by a built-in voltmeter, you can connect an oscilloscope to the connectors for a more in-depth analysis.

By the way

A couple of months ago I bought about 25 PSUs (from a PC repair company that was closing). Half working, 250-450 watts. I bought them as guinea pigs for studying and attempting repairs. The load block is just for them.

That's it. I hope it was interesting and useful. I went to test my power supplies and wish you good luck!

Today it is not uncommon to see people throwing away computer power supplies. Well, or the power supply units are just lying around idle, collecting dust.

But they can be used on the farm! In this article I will tell you what voltages can be obtained at the output of a conventional computer unit nutrition.

A small educational program about voltages and currents of a computer power supply

Firstly, do not neglect safety precautions.

If at the output of the power supply we are dealing with voltages that are safe for health, then at the input and inside it there are 220 and 110 Volts! Therefore, follow safety precautions. And make sure no one else gets hurt by the experiments!

Secondly, we need a Voltmeter or Multimeter. Using it, you can measure voltages and determine the polarity of the voltage (find plus and minus).

Thirdly, on the power supply you can find a sticker that will indicate the maximum current for which the power supply is designed for each voltage.

Just in case, subtract 10% from the written figure. This way you will get the most accurate value (manufacturers often lie).

Fourthly, the ATX type PC power supply is designed to generate constant supply voltages +3.3V, +5V, +12V, -5V, -12V. Therefore, do not try to get an alternating voltage at the output. We will expand the set of voltages by combining nominal ones.

Well, did you get it? Then let's continue. It's time to decide on the connectors and the voltages at their contacts.

Computer power supply connectors and voltages

Color coding of computer power supply voltages

As you may have noticed, the wires coming out of the power supply have their own color. It's not just like that. Each color represents voltage. Most manufacturers try to adhere to one standard, but there are some completely Chinese blocks power supply and color may not match (that’s why a multimeter can help).

In normal power supplies, the wire color markings are as follows:

• Black - common wire, ground, GND
• White - minus 5V
• Blue - minus 12V
• Yellow - plus 12V
• Red - plus 5V
• Orange - plus 3.3V
• Green - power on (PS-ON)
• Gray - POWER-OK (POWERGOOD)
• Purple - 5VSB (standby power).

Pinout of AT and ATX power supply connectors

For your convenience, I have selected a number of pictures with pinouts of all types of power supply connectors today.

First, let's study types and types of connectors(connectors) of a standard power supply.

To “power” the motherboard, an ATX connector with 24 pins or an AT connector with 20 pins is used. It is also used to turn on the power supply.

For hard drives, CDROMS, card readers and other things, MOLEX is used.

A connector for flopy drives is a rarity today. But you can find it on old power supplies.

The 4-pin CPU connector is used to power the processor. There are two of them or even double, that is, 8-pin, for powerful processors.

SATA connector - replaced the MOLEX connector. Used for the same purposes as MOLEX, but on newer devices.

PCI connectors are most often used to supply additional food for various kinds PCI express devices (most common for video cards).

Let's move on directly to pinouts and markings. Where are our cherished tensions? And here they are!

Another picture with pinouts and color codes for voltages on the power supply connectors.

Below is the pinout of the AT type power supply.

Here you go. We've sorted out the pinout of computer power supplies! It's time to move on to how to get the necessary voltages from the power supply.

Obtaining voltages from computer power supply connectors

Now that we know where to get the voltages, let's use the table I provided below. It should be used as follows: positive voltage + zero = total.

It is important to remember that the final voltage current will be determined by the minimum value based on the ratings used to obtain it.

Also do not forget that for high currents it is advisable to use a thick wire.

The most important!!! The power supply is started by shorting the wires GND And PWR SW. It works as long as these circuits are closed!

REMEMBER! Any experiments with electricity must be carried out with strict adherence to electrical safety rules!!!

Addition on connectors. Clarification of pinouts of PCIe and EPS connectors.

If the device malfunctions, the current source is first checked, and then everything else. For this purpose, a power supply tester, an oscilloscope, and voltage, current, resistance, and frequency meters are used. A regular multimeter can also be used as a tester for the power supply of a computer or other device. It can measure both current and load resistance.

Power supply device

To identify a malfunction, you need to have a general understanding of the purpose and design of the electric current source.

Currently, two types of power supplies are used: transformer and switching. The former, using a step-down transformer, convert AC 220 volts 50 hertz to the required voltage. Then it is rectified through a diode bridge, and capacitors and transistors convert it into D.C..

The second, with the help of high-voltage diodes, alternating 220 volts are first rectified, passed through a filter and converted into a pulse current with a frequency of (30-200) thousand hertz. After this, the high-frequency voltage is supplied to the transformer, and the required potential emerges from the secondary windings. Then the transformation proceeds as in transformer block nutrition.

Pulse current sources have become widespread due to their smaller dimensions and the same power.

Transformers are needed for the safety of people and to protect batteries from high voltage.

Current measurement

Having a general understanding of the operation of the current source, you can begin to check it. If we are talking about power supplies for phones, cameras and other low-power equipment with small blocks, then the current in them can be measured.

How to measure current strength is a question in a school textbook. A multimeter or ammeter is connected to the open circuit. Please pay attention to the limit value of the scale. If the multimeter allows you to measure a maximum of 10 A, then you can check a unit designed for a maximum of this current, and no more. Our current will be constant, since it has already passed through the block.

To connect the power supply, you must either cut one of the wires or disassemble the case. The circuit must be closed to the tester. Measurements are carried out quickly, within 2 seconds, so that the contacts do not have time to heat up too much.

Preparing to measure voltage

In some cases, the voltage is checked. For example, consider a computer power supply. Remove the side cover of the system box. Then disconnect all the cables going to the power source.

The bundles are assembled from conductors of different colors, each of them corresponds to a certain voltage. Contacts with black wires correspond to common (ground). The yellow conductor supplies +12 volts, red +5 volts, orange +3.3 volts. Blue corresponds to -12 V, white -5 V, purple +5VSB (standby power), gray PW-OK (Power good), green PS-ON. When the switch is on, there should be +5 V on the PS-ON and PW-OK contacts.

There is voltage on the purple wire as long as the power switch is on. back cover The computer is turned on and connected to the network. This allows you to start your computer remotely.

White is rarely used, intended for expansion cards installed in the ISA slot.

The blue wire is required for RS232, FireWire and some PCI boards extensions.

Voltage measurement

Now you can proceed directly to measurements. Checking the power supply using a multimeter is carried out in the following sequence.

In a twenty-pin connector, connectors with a green and one black wire are connected by a jumper. When they are shorted, the power supply starts up.

By turning the tester switch, the measurement mode is selected DC voltage, the range is set to 20 volts. The black test lead is connected to the common wire. Red checks the voltage at the remaining terminals. The readings must be within:

• for +5 V 4.75…5.25 V;
• for +12 V 11.4…12.6 V;
• for +3.3 V 3.14…3.47 V;
• for -12 V -10.8…-13.2 V.

If the output voltages correspond to the norm, then there should be +5 volts at the Power good terminal. This signal goes to the motherboard and allows the processor to start.

In addition to the main harness, several additional ones with four-pin connectors come out of the computer power supply. They are designed to supply voltage to rigid and optical disks. There is also color coding of signals here. Measurements are made as on the main connector.

If the readings at the terminals are within the acceptable range, then the power supply is working. This means that the failure is on the motherboard.

Finding the cause of the malfunction

If there is no voltage or the values ​​are outside the tolerance limits, you need to look for the reason for this in the power supply. To do this, you need to remove it from the system box. On the back cover, the screws holding the power source housing are unscrewed, and it is removed. Then you need to remove the protective cover of the power supply. After this, visual inspection is carried out, the presence of carbon deposits and swelling of the capacitors is checked. Batteries with such symptoms must be replaced. Further testing begins with a continuity test of the circuit in which there is no voltage.

The multimeter switches to the resistance measurement position. In this mode, the network cable must be disconnected from the power supply. One probe is connected to the contact of the connector with no potential, the second to the point where the wire is connected to the board and a measurement is made. The device should show 0 Ohm. This means that the conductor is intact. If the values ​​are non-zero, then it needs to be replaced.

Checking the entire circuit

After replacing the faulty elements, alternating current is connected to the power supply and everything is measured again with the tester. If there is no signal, then its presence is checked along the entire circuit from the connector to the output stage of the transistor that produces this voltage. This can be seen in the lamellas (strips of copper on the board). If there is no voltage on the transistor, its presence is checked on the zener diode and capacitor. If it is missing there too, then the condition of the pulse transformer is checked. The power supply is disconnected from the network, and the resistance of its windings is measured using a multimeter.

If there is no voltage at all contacts of the output connectors, then the test must begin from the point of connection network cable. The tester switches to mode AC voltage 750 volts. Then the presence of 220 volts is checked at the output of the network cable, then at the input of the diode bridge. Since the output voltage will be rectified, the tester must be switched to direct current. This way you can identify the problem and then fix it. This completes the check of the computer power supply. Current sources in most other devices are designed in the same way as the power supply discussed above. The difference may be in the output voltage ratings. If a person disassembles and checks it with his own hands computer source current, then it won’t be difficult for him to deal with the rest.

The health of any living organism depends on how and what it eats. The same can be said about a computer - with good and proper operation power supply electronic devices function “like a clock.” And vice versa: if the feeder malfunctions, working on a PC turns into torture or becomes completely impossible.

Problems with a computer power supply manifest themselves in different ways - from a lack of response to an attempt to turn it on to occasional “glitches”. Let's talk about what symptoms indicate a failure of the computer's power supply and how to check its functionality and serviceability without exposing yourself to danger.

Complete failure and malfunction of the power supply most often occur due to:

• Voltage surges in the electrical network.
• Low quality of the PSU itself.
• Inconsistencies between power supply capabilities and load consumption (computer devices).

The consequences of a malfunctioning power supply, especially in combination with poor manufacturing quality, can be not only breakdowns of the PC electronics, but also electric shock to the user.

How computer power supply problems manifest themselves

Symptoms of a malfunctioning feeder are very varied. Among them:

• PC does not turn on when pressed power buttons or turning on after repeated presses.
• Squeaking, crackling, clicking, smoke, burning smell from the power supply.
• The mains fuse on the distribution board blows when the computer is turned on.
• Discharges of static electricity from the case and connectors of the system unit.
• Spontaneous shutdowns and restarts of the PC at any time, but more often under high loads.
• Brakes and freezing (until reboot).
• Memory errors, BSoD (blue screens of death).
• Loss of devices from the system (drives, keyboards, mice, other peripheral equipment).
• Stopping the fans.
• Overheating of devices due to ineffective operation or stopping of fans.

Operating principle of the power supply

To figure out whether the power supply is working or not, you need to understand basic principles his work. In a simplified way, its function can be described as follows: converting the input AC voltage of a household electrical network into a DC output of several levels: 12 V, 5 V 5 V SB (standby voltage), 3.3 V and -12 V.

The following devices receive power from a 12-volt source:

• drives connected via SATA interface;
• optical drives;
• cooling system fans;
• processors;
• video cards.

The 12 V line wires are yellow.

Powered from 5 V and 3.3 V:

• sound, network controller and the bulk of the motherboard chips;
• RAM;
• expansion boards;
• peripheral devices connected to USB ports.

According to the ATX standard, the 5 V line is indicated by red wires, 5 V SB by purple, and 3.3 V by orange.

The computer startup circuit on the motherboard receives power from a 5 V SB (standby) source. The -12 V source is designed to power COM ports, which today can only be found on very old motherboards and specialized devices (for example, cash registers).

The above voltages are produced by all ATX standard power supplies, regardless of power. The only differences are in the level of currents on each line: the more powerful the feeder, the more current it delivers to consumer devices.

Information about the currents and voltages of individual lines can be obtained from the power supply passport, which is pasted in the form of a label on one of the sides of the device. However, nominal indicators almost always differ from real ones. This does not mean anything bad: fluctuations in values ​​within 5% are considered normal. Such minor deviations do not affect the operation of computer devices.

Among other things, a working power supply produces a Power Good or Power OK signal, which notifies the motherboard that it is working as it should and the board can start other devices. Normally, this signal has a level of 3-5.5 V and rises only when all supply voltages have reached the specified values. If the power supply does not produce Power Good, the computer will not start. If it produces too early, which is also not good, the device may turn on and turn off immediately, freeze during boot, or throw a critical error - blue screen death.

The Power Good signal is transmitted to the motherboard via the gray wire.

ATX main power supply connector pins

WITH color coded wires 12 V, 5 V, 5 V SB, 3.3 V and 3-5.5 V Power Good, we figured it out. The remaining contacts have the following voltages:

• White:-5 V. Left for compatibility with older devices.
• Blue:-12 V.
• Black: 0 V. Common wire or ground.
• Green: 3-5 V. Power On. Closing this contact to ground is equivalent to pressing the power button on the computer case. Starts the power supply. At the moment of pressing, the voltage at the button contacts should drop to 0 V.

The same voltages are present on other connectors that terminate the power supply cables. That is, in the yellow wire projection there should always be 12 V, in the red wire projection - 5 V, in the orange wire projection - 3.3 V, etc.

How to Test a Power Supply Using a Multimeter

The compliance of all voltages that the feeder produces with the specified levels and the preservation of their values ​​under any load (if they do not exceed the capabilities of the power supply) indicate that the device is operational and, most likely, in good working order. And to determine them, you will need a multimeter - an inexpensive compact device that can be purchased at almost any electrical goods store.

Multimeters (testers), of course, are different. Among them there are expensive high-precision models with mass additional functions, but for our purposes a simple one is sufficient. To check the power supply, we don’t need measurements down to thousandths of a volt; tenths and sometimes hundredths are enough.

Conditions for taking measurements

Measurements of voltages at the power supply outputs should be made under conditions where failure occurs. If the problem appears in the first seconds and minutes of PC operation, the device readings should be taken immediately after turning on. If you are working intensively, to obtain reliable results, the computer should be loaded, for example, with a heavy game or a program designed for this (for example, the OCCT utility, Power Supply test).

To track changes in supply voltages during PC operation, measurements are best taken continuously over several minutes or tens of minutes. If for some reason this is difficult, you can take one-time measurements at certain time intervals.

The result of a single measurement during a floating fault is often not an indicator, since in the case unstable work feeder voltage values ​​(or one of them) can constantly change.

The procedure for taking measurements

• Turn on the computer and bring it into the state where the problem occurs.
• Switch the multimeter to DC voltage measurement mode (the icon on the instrument panel is surrounded by a yellow frame). Set the upper scale limit to 20 V.
• Connect the black probe to any metal pad on the motherboard where the voltage is 0 V (for example, near a mounting hole), or to a pin in the connector that the black wire goes to.
• Place the red probe in the measurement area (in the connector opposite the corresponding wire). The number that you see on the tester display is the voltage indicator in Volts.

How to check the functionality of the feeder if the computer does not turn on

One of common reasons the computer’s lack of response to pressing the power button is precisely the failure of the power supply. To confirm or refute this version, all we need is a metal clip or tweezers, with which we can simulate pressing a button. Remember, a little earlier we found out that for this you need to short-circuit the green and black wires on the 24-pin connector of the power supply unit, which is connected to the motherboard? Just before that it needs to be disconnected from it.

• Connect a certain load—an energy consumer—to the power supply, which is disconnected from the motherboard and computer devices. For example, an unused optical drive or light bulb. Please be aware that if the power supply is faulty, the connected device may be damaged. Therefore, use what you don't mind.
• Plug in the power supply.
• Use a paper clip to connect the 2 pins opposite the green and black wires. If the feeder shows signs of life - it starts the fan inside and turns on the connected load, then it is operational. However, performance does not mean serviceability, that is, this diagnostic method only allows you to differentiate a working device from a completely non-working one.

What diagnostic methods for computer power supplies still exist?

Checking the power supply with a multimeter and a paper clip is enough to identify its malfunction in about 70-80% of cases. If you do not plan to repair it in the future, then you can limit yourself to this. In professional diagnostics of power supplies, not only these, but also other methods are used to localize the defect. Including:

• Checking the output voltage ripple using an oscilloscope. This is a rather expensive device, so it is unlikely that anyone will decide to buy it for a one-time job.
• Disassembly, inspection, checking voltages and resistances of elements printed circuit board for compliance with standards. It is dangerous to do this without special training, since power supplies accumulate household voltage in some parts. Accidentally touching any live part may result in electric shock.
• Current measurement. This is done using an ammeter built into the tester, which is connected to the break in the line being tested. To create a gap, board elements are usually desoldered.
• Testing on stands with specially selected equipment in various operating modes.

In short, there are quite a few methods for diagnosing power supplies, but not all of them are applicable or advisable at home. Except for research purposes, if, of course, the owner is interested in this.