Power supply for a computer 350w do-it-yourself repair

In detail: do-it-yourself power supply for a 350w computer repair from a real master for the site my.housecope.com.

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

The figure shows an image of a block diagram typical for switching power supplies of system blocks.

ATX switching power supply device

Designations indicated:

A - network filter unit;
B - low-frequency type rectifier with a smoothing filter;
C - cascade of the auxiliary converter;
D - rectifier;
E - control unit;
F - PWM controller;
G - cascade of the main converter;
H - high-frequency type rectifier, equipped with a smoothing filter;
J - PSU cooling system (fan);
L – output voltage control unit;
K - overload protection.
+5_SB - standby power supply;
P.G. - information signal, sometimes referred to as PWR_OK (required to start the motherboard);
PS_On - a signal that controls the launch of the PSU.

To carry out repairs, we will also need to know the pinout of the main power connector (main power connector), it is shown below.

PSU plugs: A - old-style (20pin), B - new (24pin)

To start the power supply, you need to connect the green wire (PS_ON #) to any black zero. This can be done using a regular jumper. Note that for some devices, the color marking may differ from the standard one, as a rule, unknown manufacturers from China are guilty of this.

It must be warned that turning on switching power supplies without load significantly reduces their service life and can even cause a breakdown. Therefore, we recommend assembling a simple load block, its diagram is shown in the figure.

Video (click to play).

Load block diagram

It is desirable to assemble the circuit on resistors of the PEV-10 brand, their ratings are: R1 - 10 Ohms, R2 and R3 - 3.3 Ohms, R4 and R5 - 1.2 Ohms. Cooling for resistances can be made from an aluminum channel.

It is undesirable to connect the motherboard as a load during diagnostics or, as some "craftsmen" advise, an HDD and CD drive, since a faulty PSU can disable them.

We list the most common malfunctions typical for switching power supplies of system units:

the mains fuse blows;
+5_SB (standby voltage) is absent, as well as more or less than the allowable one;
voltage at the output of the power supply (+12 V, +5 V, 3.3 V) does not correspond to the norm or is absent;
no signal P.G. (PW_OK);
PSU does not turn on remotely;
cooling fan does not rotate.

After the power supply is removed from the system unit and disassembled, first of all, it is necessary to inspect for the detection of damaged elements (darkening, changed color, integrity violation). Note that in most cases, replacing the burnt part will not solve the problem, checking the binding will be required.

Visual inspection allows you to detect "burnt" radio elements

If none are found, proceed to the next algorithm of actions:

If a faulty transistor is found, then before soldering a new one, it is necessary to test its entire piping, consisting of diodes, low-resistance resistances and electrolytic capacitors. We recommend replacing the latter with new ones that have a large capacity. A good result is obtained by shunting electrolytes with ceramic capacitors 0.1 μF;

Checking the output diode assemblies (Schottky diodes) with a multimeter, as practice shows, the most typical malfunction for them is a short circuit;

Diode assemblies marked on the board

checking the output capacitors of the electrolytic type. As a rule, their malfunction can be detected by visual inspection. It manifests itself in the form of a change in the geometry of the body of the radio component, as well as traces of electrolyte leakage.

It is not uncommon for an outwardly normal capacitor to be unusable during testing. Therefore, it is better to test them with a multimeter that has a capacitance measurement function, or use a special device for this.

Video: correct ATX power supply repair. <>

Note that non-working output capacitors are the most common malfunction in computer power supplies. In 80% of cases, after replacing them, the PSU performance is restored;

Capacitors with broken case geometry

resistance is measured between the outputs and zero, for +5, +12, -5 and -12 volts this indicator should be in the range from 100 to 250 ohms, and for +3.3 V in the range of 5-15 ohms.

In conclusion, we will give some tips for finalizing the PSU, which will make it work more stable:

in many inexpensive units, manufacturers install rectifier diodes for two amperes, they should be replaced with more powerful ones (4-8 amperes);
Schottky diodes on channels +5 and +3.3 volts can also be put more powerful, but at the same time they must have an acceptable voltage, the same or more;
it is advisable to change the output electrolytic capacitors to new ones with a capacity of 2200-3300 microfarads and a rated voltage of at least 25 volts;
it happens that diodes soldered together are installed on the +12 volt channel instead of a diode assembly, it is advisable to replace them with a Schottky diode MBR20100 or similar;
if capacitances of 1 uF are installed in the piping of the key transistors, replace them with 4.7-10 uF, designed for a voltage of 50 volts.

Such a minor refinement will significantly extend the life of the computer power supply.

Very interesting to read:

In today's world, the development and obsolescence of personal computer components is very fast. At the same time, one of the main components of a PC - an ATX form factor power supply - is practically has not changed its design for the last 15 years.

Therefore, the power supply of both the ultra-modern gaming computer and the old office PC work on the same principle, have common troubleshooting techniques.

A typical ATX power supply circuit is shown in the figure. Structurally, it is a classic pulse unit on a TL494 PWM controller, triggered by a PS-ON (Power Switch On) signal from the motherboard. The rest of the time, until the PS-ON pin is pulled up to ground, only the Standby Supply is active with +5 V at the output.

Consider the structure of the ATX power supply in more detail. Its first element is
mains rectifier:

Its task is to convert alternating current from the mains to direct current to power the PWM controller and the standby power supply. Structurally, it consists of the following elements:

Fuse F1 protects the wiring and the power supply itself from overload in the event of a PSU failure, leading to a sharp increase in current consumption and, as a result, to a critical increase in temperature that can lead to a fire.
A protective thermistor is installed in the "neutral" circuit, which reduces the current surge when the PSU is connected to the network.
Next, a noise filter is installed, consisting of several chokes (L1, L2), capacitors (C1, C2, C3, C4) and a choke with counter winding Tr1. The need for such a filter is due to the significant level of interference that the pulse unit transmits to the power supply network - this interference is not only picked up by television and radio receivers, but in some cases can lead to malfunctioning of sensitive equipment.
A diode bridge is installed behind the filter, which converts alternating current into a pulsating direct current. The ripples are smoothed out by a capacitive-inductive filter.

Further, the constant voltage, which is present all the time while the ATX power supply is connected to the outlet, is supplied to the control circuits of the PWM controller and the standby power supply.

Standby power supply - This is a low-power independent pulse converter based on the T11 transistor, which generates pulses, through an isolation transformer and a half-wave rectifier on the D24 diode, feeding a low-power integrated voltage regulator on the 7805 chip. Although this circuit is, as they say, time-tested, its significant drawback is high voltage drop across the 7805 stabilizer, leading to overheating under heavy load. For this reason, damage in circuits powered from a standby source can lead to its failure and subsequent inability to turn on the computer.

The basis of the pulse converter is PWM controller. This abbreviation has already been mentioned several times, but not deciphered. PWM is pulse-width modulation, that is, changing the duration of voltage pulses at their constant amplitude and frequency. The task of the PWM block, based on a specialized TL494 microcircuit or its functional analogues, is to convert a constant voltage into pulses of the appropriate frequency, which, after an isolation transformer, are smoothed out by output filters. Voltage stabilization at the output of the pulse converter is carried out by adjusting the duration of the pulses generated by the PWM controller.

An important advantage of such a voltage conversion circuit is also the ability to work with frequencies much higher than 50 Hz of the mains. The higher the current frequency, the smaller the dimensions of the transformer core and the number of turns of the windings are required. That is why switching power supplies are much more compact and lighter than classic circuits with an input step-down transformer.

The circuit based on the T9 transistor and the stages following it is responsible for turning on the ATX power supply. At the moment the power supply is connected to the network, a voltage of 5V is supplied to the base of the transistor through the current-limiting resistor R58 from the output of the standby power source, at the moment the PS-ON wire is closed to ground, the circuit starts the TL494 PWM controller. In this case, the failure of the standby power source will lead to the uncertainty of the operation of the power supply startup circuit and the probable failure of switching on, as already mentioned.

The main load is borne by the output stages of the converter. First of all, this concerns the switching transistors T2 and T4, which are installed on aluminum radiators. But at a high load, their heating, even with passive cooling, can be critical, so the power supplies are additionally equipped with an exhaust fan. If it fails or is very dusty, the probability of overheating of the output stage increases significantly.

Modern power supplies are increasingly using powerful MOSFET switches instead of bipolar transistors, due to the significantly lower open-state resistance, providing greater converter efficiency and therefore less demanding cooling.

Video about the computer power supply unit, its diagnostics and repair

Initially, ATX standard computer power supplies used a 20-pin connector to connect to the motherboard (ATX 20-pin). Now it can only be found on outdated equipment. Subsequently, the growth in the power of personal computers, and hence their power consumption, led to the use of additional 4-pin connectors (4-pin).Subsequently, the 20-pin and 4-pin connectors were structurally combined into one 24-pin connector, and for many power supplies, the part of the connector with additional contacts could be separated for compatibility with old motherboards.

The pin assignment of the connectors is standardized in the ATX form factor as follows according to the figure (the term “controlled” refers to those pins on which the voltage appears only when the PC is turned on and is stabilized by the PWM controller):

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 a voltage that is outside the permissible range, then this can cause the failure of important and expensive components.

In such a unit, with the help of an inverter, the rectified mains voltage is converted into a high-frequency alternating voltage, from which the low voltage flows necessary for the operation of the computer are formed.

The ATX power supply circuit consists of 2 nodes - a mains voltage rectifier and a voltage converter for a computer.

Mains rectifier is a bridge circuit with a capacitive filter. A constant voltage of 260 to 340 V is formed at the output of the device.

The main elements in the composition voltage converter are:

an inverter that converts direct voltage to alternating;
high-frequency transformer 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 transistor control signal amplifiers, protection and stabilization circuits, and other elements.

The causes of malfunctions in the power supply can be:

surges and fluctuations in the mains voltage;
poor-quality manufacturing of the product;
overheating due to poor fan performance.

Malfunctions usually lead to the fact that the computer's system unit stops starting or turns off after a short period of work. In other cases, despite the operation of other blocks, the motherboard does not start.

Before starting repairs, you must finally make sure that it is the power supply that is faulty. In doing so, you must first check the operation of the network cable and the network switch. After making sure that they are in good condition, you can disconnect the cables and remove the power supply from the system unit case.

Before you turn on the PSU autonomously again, you need to connect the load to it. To do this, you need resistors that are connected to the appropriate terminals.

First you need to check motherboard effect. To do this, 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 matches the GND pin). For a 24-pin connector, these will be pins 16 and 17, respectively.

After removing the cover from the power supply, you must immediately clean all the dust from it with a vacuum cleaner. It is precisely 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 a severe temperature regime. Failed 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 a capacitor does not indicate a malfunction. If, by indirect signs, there is a suspicion of poor performance, then you can check the capacitor with a multimeter. But for this it needs to be removed from the circuit.

A power supply failure may also be due to a low voltage diode failure. To check, it is necessary to measure the resistance of the forward and reverse transitions of the elements using a multimeter. To replace faulty diodes, the same Schottky diodes must be used.

The next fault that can be identified visually is the formation of ring cracks that break the contacts. To detect such defects, it is necessary to carefully examine the printed circuit board. To eliminate such defects, it is necessary to use careful soldering of the cracks (for this you need to know how to properly solder with a soldering iron).

Resistors, fuses, inductors, transformers are inspected in the same way.

In the event that the fuse is blown, it can be replaced with another one or repaired. The power supply uses a special element with solder leads. To repair a faulty fuse, it is unsoldered from the circuit. Then the metal cups are heated and removed from the glass tube. Then choose the wire of the desired diameter.

The required wire diameter for a given current can be found in the tables. For the 5A fuse used in the ATX power supply circuit, 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.

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 complicated device, but in some cases you can repair it yourself.

Good day.
Today they brought me this old man.Powerman 350w. From the words of the client: The computer hung on a black screen, decided that the power supply was to blame, climbed to “fix”, switched the power mode from 220v to 110v. I think that it was not difficult to guess further.
We remove the casing and, in principle, you can immediately replace the fuse.In the photo, the fuse is already soldered. We continue with the external examination.A burnt varistor timidly peeks out from behind the capacitor. Removes capacitors. there is a break.Hmm, not weakly rasfigachilo them. We solder them together with the radiator. And we check the only surviving transitor of the duty room.Worker. Judging by the diagrams from similar blocks, there were MJE13009G 400 volts 12 amps. After a bit of climbing through the bins, I found these, but in a different building.We solder this case back, and connect a light bulb to the gap to check the high-voltage part of the unit. We turn on the unit, the light blinks, which means the high-voltage circuit is in order. We check the standby voltage.We solder the light bulb, try to turn on the unit. And it starts, all the voltage is normal. It remains to test the load. I'm hooking up to a test computer. I turn on the AIDA, load the computer and leave it for a couple of hours, simultaneously controlling the voltage of 5 and 12 volts.P.S. I don't work at a service center. It's my hobby to repair appliances.It seems to me that this, if repaired, is clean for fun, for myself or as a friend.And even then, if something is not critical (solder the conduits)It is easier to replace it with FSP which new one to take for 1000r. power man used to be a fucking brand. the standard of reliability. like delta or fsp. really it was a long time ago. and there are no new pavermen for sale.Won, the link to Yandexmarket is below 350 watt fsp for 1100But okay, here's the real fsp for 1133))it does not have pfc (power factor corrector) - because of this, low efficiency (70%), I generally keep quiet about conveniences like turning off the fan at low heat or regulating fan speed.to put such a thing in a new computer (even an office one) - do not respect your earsSo this PowerMan of the same class)And exactly the same.I agree. only the old power supply has been changed, and this one is sold even now, although the design of the power supply has improved.Repair power supply 350wTS is probably visiting for his birthday?as far as I know, old PSUs have low efficiency90% of cheap power supplies are made according to the same scheme with minor variations. Now fashionable things like PFC, etc. have been added. and, in fact, everything. even PWM controllers are the same TL494, UC3842 and their relabeled counterpartsBROTHER! I have had exactly the same powerhouse for 12 years now, and not a hint of problems!Switch the power mode from 220v to 110v.I once switched during work. fucked up a lot, i liked it =)Against the background of the carpet, everything should work 😀 (9 photos)Tell me, what city are you from? do you repair for money? =)Does it make sense to restore it, given the price?I have a couple of boxes lying around, for donors, because in a power supply unit that has plowed a broken trunk for a couple of years, it’s not enough to replace it, and it’s also going to be fat for him to change conduits with a fan.So for repairs I take more or less expensive power supplies from 500W and above - it makes sense to restore them.My first system had one like this. Even despite the then zero knowledge about the care of equipment, he worked for a long time. Until the pulse transformer burned out. Image - Power supply for a computer 350w do-it-yourself repair

Despite its apparent power, a personal computer is a fragile thing. To disable any part, simply careless handling of it is enough. For example, do not clean the system unit and its components. As a result, a lot of dust is formed on the parts, which negatively affects the operation of the device as a whole.

One of the most important components of a PC is the power supply. It is he who distributes electricity throughout the system unit and controls the voltage level. Therefore, the breakdown of this device can be attributed to one of the most unpleasant. Nevertheless, everyone can do repairs and fix the problem with their own hands.

The most critical situation is when the computer does not respond to power button. This means that important points were missed that could indicate an imminent breakdown. For example, an unnatural sound during operation, a long turn on of the computer, an independent shutdown, etc. Or maybe such malfunctions were noticed, but it was decided not to resort to repairs.

In addition to the most critical moments, there are several signs that help identify problems in the operation of a computer power supply:

The occurrence of various errors when turning on the PC.
Sudden computer restarts.
Increasing the volume of coolers (small fans).
Various errors when the PC is turned on.
Termination of the hard drive or some coolers.
Loud beeping from the system unit (indicates overheating).
Electric shock when touching the case.

Such signs indicate the need for an early repair, which can be done by hand. However, there are also more serious problemsclearly indicating a serious problem. For instance:

"Screen of death" (blue screen when the device is turned on or working).
The appearance of smoke.
No reaction to turn on.

Most people in the event of such problems turn to the master for repairs. As a rule, a computer specialist advises to purchase a new power supply, and then install it in place of the old one. Nevertheless, with the help of repair, you can “reanimate” a non-working device with your own hands.

To completely solve the problem, you need to understand why it could appear. The most common computer power supply fails for three reasons:

Voltage fluctuations.
Poor quality of the product itself.
Inefficient operation of the ventilation system, leading to overheating.

In most cases, such malfunctions lead to the fact that the power supply does not turn on or stops working after a short time. In addition, the above problems may adversely affect the motherboard. If this happens, then do-it-yourself repairs are not enough here - it will be necessary to change the part to a new one.

Less commonly, malfunctions in the computer's power supply occur due to the following reasons:

Low-quality software (poor OS optimization has a bad effect on the operation of all components).
Lack of component cleaning (large amounts of dust make coolers run faster).
A lot of extra files and "garbage" in the system itself.

As mentioned above, the power supply is a rather fragile thing. Nevertheless, it is very important for the computer as a whole, so you should not deprive this component of attention. Otherwise, repair is inevitable.

The power supply in the computer is responsible for the distribution and conversion of electric current. The fact is that each element in a PC needs its own voltage level. In addition, AC power is used in electrical networks, while computer components operate on DC. Therefore, the device of the power supply is quite specific and you need to know it for do-it-yourself repairs.

In every BP There are 9 important components:

Without having at least an approximate idea of \u200b\u200bthe device of the power supply, it is impossible to fully carry out independent repairs.

Before you start solving a problem on a computer with your own hands, you need to think about your own safety. Repairing such a device is a dangerous occupation. Therefore, first of all, you need to work thoughtfully and without haste.

For greater security, remember a few important rules:

Work only with the power supply turned off. Despite the banality of the advice, this is a very important point. No one is immune from the “fool syndrome”, so it’s better to check once again that everything is turned off, and only then start repairing.
In order to preserve the components, as well as to avoid "fireworks", it is recommended to install a 100 watt light bulb instead of a fuse. If the light remains on when the power supply is turned on, then the network is closed somewhere. If it lights up and immediately goes out, then everything is in order.
Power capacitors are energized for a particularly long time. Therefore, even after disconnecting the PSU from the network, you should not immediately get to work.
It is better to check the operation of the device away from flammable substances, since there is a risk of a short circuit and "fireworks" of sparks.

To make the repair of the power supply simple but effective, each home master will need certain tools for work. All these products can be easily found at home, asked from neighbors / friends or purchased at the store. Fortunately, they are inexpensive.

So to repair you will need the following tools:

Soldering station with built-in power control or several soldering irons, each of which is designed for a certain power.
Solder and flux for soldering components.
To remove solder - braid or suction.
Several screwdrivers with different tips.
Multimeter.
Side cutters (devices for cutting plastic "clamps" that fasten wires).
Light bulb 100 watts.
Tweezers (for removing small components).
Alcohol or refined gasoline.
You may need an oscilloscope (if the cause of the problem is not determined).

First you need disassemble the power supply. To do this, you only need a screwdriver and accuracy. When unscrewing the bolts, you do not need to shake the PSU in order to quickly fix the problem. Careless handling of it can lead to the fact that do-it-yourself repairs will be simply useless.

For the correct statement of the "diagnosis" it is necessary to carry out primary diagnostics, as well as a visual inspection of the device. Therefore, first of all, you need to pay attention to the power supply fan. If the cooler cannot spin freely and gets stuck in a certain place, then this is clearly the problem.

In addition to the fan of the product, you should also inspect the device as a whole. After a long service life, a lot of dust accumulates in it, which has a negative effect and makes it difficult for the PSU to work normally. Therefore, it is imperative to clean the product from dust accumulation.

Also, some products are out of order. due to voltage fluctuations. Therefore, it is necessary to conduct a visual inspection for burnt parts. This sign is easy to identify by swelling of the capacitors, darkening of the textolite, charring of the insulation or broken wires.

Finally, it’s worth moving on to the most important point - do-it-yourself PSU repair. For convenience, the entire process will be presented in the form of a list. Therefore, it is recommended not to "jump" from one point to another, but act in the following order:

It happens that outwardly everything is in order: the components are not melted, there are no cracks or broken contacts. What is the problem then? It is best to carefully examine all the details again. It is possible that some kind of malfunction was overlooked due to inattention. If no problems were found during the secondary inspection, then in 90% of cases the malfunction lies in the standby power supply or in the PWM controllerusing wide pulse modulation.

To fix the standby voltage problem, you need to know the basics of how the power supply works. This PC component works almost always. Even when the computer itself is turned off (not disconnected from the network), the unit operates in standby mode. This means that the PSU sends “standby signals” of 5 volts to the motherboard so that when the PC is turned on, it can start the unit itself and other components.

When starting the system, the motherboard checks the voltage for all elements. If everything is in order, it is formed response signal "Power good" and the system starts up. If there is a shortage or excess voltage, the system start is canceled.

This means that first of all on the board you need to check the presence of 5 V on the PS_ON and + 5VSB contacts. When checking, the absence of voltage or its deviation from the nominal value is usually detected. If the problem is observed in PS_ON, the reason is in the PWM controller. If the fault is with the + 5VSB contact, then the problem lies in the electric current conversion device.

It would also be useful to check the PWM itself. True, for this you need an oscilloscope. To check, you need to unsolder the PWM and use an oscilloscope to check the contacts by ringing (OPP, VCC, V12, V5, V3.3). For better ringing, the test must be carried out relative to the ground. If the resistance between the ground and any of the contacts (of the order of several tens of ohms), then the PWM must be replaced.

Self-repair of the power supply is a rather complicated process, which will require the necessary tools, basic knowledge about the operation of the PSUas well as accuracy and attention to detail. Nevertheless, each person, with the proper approach, can repair the unit, despite its complex structure. Therefore, you should remember that everything is in your hands.

So, the Chinese combined the ventilation of the case with the airflow of the block.
And the fan on the process. also for breakdown.
And powerful generator lamps. also for breakdown.It's all about overpressure.This is so that no one has any questions, they came up with such blocks a long time ago, where not just for injection, but directly a wind tunnel,
frankly, it really blows like a vacuum cleaner, and then at half power, but it was not possible to disperse more Image - Power supply for a computer 350w do-it-yourself repair

P.S Boasting is not a good thing

I just restored more than a dozen blocks and not ONE. didn’t fail due to overheating, one wheelbarrow rumbled for how long with a jammed fan, the plate turned blue, everything works to this day
It can be seen that this alteration dates back to the time of AT blocks, where indeed the air inlets were much smaller, they managed to bend 90 degrees with pliers - they added air flow

Added (08.11.2014, 13:48)
———————————————
1 swollen conder changed the second piece of sticker 100uF

I usually just disassemble such power supplies into parts right away, their repair does not make sense.
We had them with a different sticker (LC-300ATX, DR-300), but inside everything is the same, right down to the location of the parts, and the same problems. Repaired them several times, but they do not last long.And the worst thing is that they can easily kill the motherboard (and everything else too!).

In your photo, I see at least three dead capacitors, you said that you only changed two.
My advice to you is don't waste your time on it. At best, even already repaired, it will be given to you in a month. half a year the maximum will burn nafik a materinka.

For a more accessible explanation of this material, I strongly recommend reading the article on the basics of repairing computer power supplies.

So, they gave a 350-watt Power Man power supply for repair

What do we do first? Well, how what? External and internal inspection. We look at the "offal". Are there any burnt radioelements? Maybe somewhere the board is charred or the capacitor exploded, or it smells like burnt silicon? All this is taken into account during the inspection. Be sure to look at the fuse. If it burned out, then we put a temporary jumper in its place for about the same number of amperes, and then we measure the input resistance through two network wires. This can be done on the power supply plug with the "ON" button turned on. It should NOT be too small, otherwise, when the power supply is turned on, the network wires will be shorted again.

If everything is OK, we turn on our power supply to the network using the network cable that comes with the power supply, and do not forget about the power button if you had it in the off state.

Next, measure the voltage on the purple wire

My patient showed 0 volts on the purple wire. Hmm, and really not furychit. I take a multimeter and ring the purple wire to ground. Ground is black wires labeled COM. COM is short for "common", which means "general". There are also some types of, so to speak, "lands":

As soon as I touched the ground and the purple wire, my cartoon made a meticulous “ppeeeeeeeeeeep” signal and showed zeros on the display. Short circuit for sure.

Well, let's look for a circuit for this power supply. Googling the expanses of Runet, I finally found the scheme. But I found only on Power Man 300 Watts, but they will still be similar. The differences in the circuit were only in the serial numbers of the radio components on the board. If you can analyze the printed circuit board for circuit compliance, then this does not become a big problem.

And here is the schematic for Power Man 300W. Click on it to enlarge it in full size.

As we can see in the diagram, the standby power, hereinafter referred to as the duty room, is denoted as + 5VSB:

Directly from it comes a zener diode with a nominal value of 6.3 volts to the ground. And as you remember, a zener diode is the same diode, but it is connected in reverse circuits. The zener diode uses the reverse branch of the current-voltage characteristic. If the zener diode were alive, then our + 5VSB wire would not short to ground. Most likely, the zener diode burned out and the P-N junction was destroyed.

What happens during the combustion of various radio components from a physical point of view? First, their resistance changes. For resistors, it becomes infinite, or in other words, it goes into a break. With capacitors, it sometimes becomes very small, or in other words, goes into a short circuit. With semiconductors, both of these options are possible, both a short circuit and an open circuit.

In our case, we can only check this in one way, by removing one or both legs of the zener diode at once, as the most likely culprit in the short circuit. Next, we will check whether the short circuit between the duty room and the ground has disappeared or not. Why is this happening?

Here are some simple tips:

1) When connected in series, the rule more than more works, in other words, the total resistance of the circuit is greater than the resistance of the largest of the resistors.

2) With a parallel connection, the opposite rule works, less than the smaller one, in other words, the final resistance will be less than the resistance of the resistor of the smaller rating.

You can take arbitrary values of the resistances of the resistors, calculate it yourself and see for yourself.Let's try to think logically, if we have one of the resistances of parallel connected radio components equal to zero, what readings will we see on the multimeter screen? That's right, also equal to zero ...

And until we eliminate this short circuit by soldering one of the legs of the part that we consider problematic, we will not be able to determine in which part we have a short circuit. The thing is that with a sound continuity, ALL parts connected in parallel with a part that is in a short circuit will ring shortly with a common wire!

We are trying to solder the zener diode. As soon as I touched it, it fell apart. No comment…

We check whether the short circuit in the duty room and mass circuits has been eliminated, or not. Indeed, the short circuit is gone. I went to the radio store for a new zener diode and soldered it. I turn on the power supply, and ... I see how my new, just bought zener diode emits magic smoke) ...

And then I immediately remembered one of the main rules of the repairman:

If something burned out, first find the cause of this, and only then change the part to a new one or you risk getting another burned part.

Swearing obscenities to myself, I bite the burned-out zener diode with side cutters, and turn on the power supply again.

So it is, the duty room is too high: 8.5 volts. The main question is spinning in my head: “Is the PWM controller still alive, or have I already burned it safely?”. I download the datasheet for the microcircuit and see the maximum supply voltage for the PWM controller, equal to 16 Volts. Uff, it seems like it should carry ...

I start to google on my problem on special sites dedicated to the repair of ATX power supplies. And of course, the problem of the overvoltage of the duty room turns out to be a banal increase in the ESR of electrolytic capacitors in the duty room circuits. We are looking for these conders on the diagram and check them.

I remember my assembled ESR meter

It's time to test what he can do.

I check the first capacitor in the duty circuit.

I'm waiting for a value to appear on the multimeter screen, but nothing has changed.

I understand that the culprit, or at least one of the culprits of the problem, has been found. I solder the capacitor to exactly the same one, at face value and operating voltage, taken from the donor board of the power supply. I want to go into more detail here:

If you decide to put an electrolytic capacitor in the ATX power supply not from a donor, but a new one from the store, be sure to buy LOW ESR capacitors, not ordinary ones. Ordinary capacitors do not work well in high-frequency circuits, but in the power supply, just such circuits.

So, I turn on the power supply and again measure the voltage at the duty room. Taught by bitter experience, I am no longer in a hurry to install a new protective zener diode and measure the voltage on the duty room, relative to the ground. The voltage is 12 volts and a high-frequency whistle is heard.

Again I sit down to google on the problem of overvoltage at the duty room, and on the site rom.by, dedicated to both the repair of ATX PSUs and motherboards, and in general all computer hardware, I find my malfunction by searching for typical malfunctions of this power supply. It is recommended to replace the 10uF capacitor.

I measure the ESR on the Conder .... Ass.

The result, as in the first case: the device goes off scale. Some say, they say, why collect some devices, such as swollen non-working capacitors, so you can see - they are swollen, or opened with a rose

Yes, I agree with this. But this only applies to large capacitors. Capacitors of relatively small denominations do not swell. In their upper part there are no notches on which they could open up. Therefore, it is simply impossible to determine their performance visually. It remains only to change them to known working ones.

So, having gone through my boards, I also found the second capacitor I needed on one of the donor boards. Just in case, his ESR was measured. It turned out to be normal.After soldering the second capacitor into the board, I turn on the power supply with a key switch and measure the standby voltage. What was required, 5.02 volts ... Hooray!

I measure all other voltages at the power supply connector. All are within the norm. Operating voltage deviations less than 5%. It remains to solder the stub at 6.3 Volts. I thought for a long time why the zener diode is exactly 6.3 Volts when the duty voltage is +5 Volts? It would be more logical to put it on 5.5 volts or similar if it stood to stabilize the voltage on the duty room. Most likely, this zener diode is here as a protective one, so that if the voltage on the duty room rises above 6.3 Volts, it burns out and short circuits the duty room, thereby turning off the power supply and saving our motherboard from burning when it enters her overvoltage through the duty room.

The second function of this zener diode, apparently, is to protect the PWM controller from overvoltage. Since the duty room is connected to the power supply of the microcircuit through a fairly low-resistance resistor, therefore, almost the same voltage is supplied to the 20th leg of the power supply of the PWM microcircuit as is present in our duty room.

So, what conclusions can be drawn from this repair:

1) All parts connected in parallel influence each other during the measurement. Their values of active resistances are calculated according to the rule of parallel connection of resistors. In the event of a short circuit on one of the radio components connected in parallel, the same short circuit will be on all other components that are connected in parallel with this one.

2) To identify faulty capacitors, one visual inspection is not enough and it is necessary either to change all faulty electrolytic capacitors in the circuits of the problematic unit of the device to obviously working ones, or to reject them by measuring with an ESR meter.

Video (click to play).

3) Having found any burned-out part, we are not in a hurry to change it to a new one, but we are looking for the reason that led to its combustion, otherwise we risk getting another burned-out part.

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