How to check an optocoupler in a switching power supply. We repair a switching source, power supply, voltage converter ourselves, with our own hands
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Industrial power supplies often fail, sometimes even high-quality and expensive samples. In this case, an ordinary person most often throws away and acquires a new one, but the cause of the breakdown may be insignificant, and for the radio amateur, such devices are of considerable interest in terms of studying and the possibility of returning to working capacity. Despite the fact that devices that cost a lot of money are often thrown away.
We suggest users to consider a simple repair of a stabilized pulse-type power supply based on a flyback generator with feedback by current and voltage, which, in addition to stabilization, allows for overload protection. The unit is powered from an alternating current with a voltage of 100 to 240 Volts and a frequency of 50/60 Hertz and produces a constant voltage of 12 Volts 2 Amperes.
The malfunction described here is quite common in power supplies of this type and has the following symptoms: the output voltage periodically appears and disappears with a certain frequency, which is visually observed as flashes and extinguishing of the output power indicator LED:
If the indicator LED is not installed, then a similar symptom can be detected with a dial-up voltmeter by connecting it to the output of the power supply. In this case, the voltmeter needle will periodically deviate to a certain value and come back (maybe not completely). This phenomenon is observed due to the operation of the protection of the device, when the voltage or current at certain points exceeds the permissible value.
This can happen both with a short circuit and with an open circuit. A short circuit most often occurs during the breakdown of capacitors or semiconductor radioelements, such as diodes or transistors. A break can be observed both in semiconductors and resistors. In any case, first of all, you should visually inspect the printed circuit board and the radio elements installed on it.
Diagnostics of the power supply before repair
It is best to do visual diagnostics using a magnifying glass:
A burnt-out resistor with position number R18 was found on the board, when it was dialed, it was broken and the contact was broken:
Power supply repair step by step with photo
The resistor could burn out when the rated power dissipation was exceeded for a long time. The burned out resistor was soldered out, and its seat was cleaned:
To replace the resistor, you need to find out its value. For this, a known good power supply unit was disassembled. The specified resistor turned out to be with a resistance of 1 Ohm:
Further along the circuit of this resistor, a punctured capacitor with the position number C6 was found, the continuity of which showed its low resistance, and therefore unsuitability for further use:
It was just the breakdown of this capacitor that could cause the resistor to burn out and further inoperability of the entire device as a whole. This capacitor has also been removed from its place, you can compare how small it is:
The broken capacitor is comparable to a match head, such a small detail caused the breakdown of the power supply. Next to it on the board, parallel to it, there is a second capacitor of the same, which survived. Unfortunately, there was no capacitor for replacement, and all hopes lay on the remaining second capacitor. But in place of the burned out resistor, a resistor with the required resistance of 1 Ohm was selected, but not surface mounting:
This resistor was installed on the seat of the burned-out one, the soldering points were cleaned from the remnants of the flux, and the seat of the punched capacitor was varnished for better insulation and eliminating the possibility of air breakdown of this place:
After a test switch-on, the power supply started up in normal mode and the indicator LED stopped blinking:
Subsequently, the installed resistor was nevertheless replaced with a surface mount resistor and a second layer of varnish was applied in place of the removed capacitor:
Of course, it would be ideal to install a second capacitor, but even without it, the power supply works fine, without extraneous noise and LED flickering:
After plugging the adapter into the network, the output voltage was measured, it turned out to be within the normal range, namely 11.9 Volts:
At this point, the repair of the device can be considered complete, since it returned to working capacity and can continue to be used for its intended purpose. It should be noted that the block is made according to a very good scheme, which, unfortunately, it was not possible to sketch.
At the moment, according to a quick external examination, one can distinguish a good network and output filter, a well-thought-out control circuitry for a power transistor and a good stabilization of the output voltage. The physical design of the device is also at a high level, the installation is rigid and even, the soldering is clean, and precision radioelements are used. All this allows us to obtain a high quality device with precisely specified parameters and characteristics.
- Read more about
Semiconductors and capacitors in high-voltage circuits are especially dangerous, which, in the event of a breakdown, can lead to irreversible consequences for the entire device if it is turned on repeatedly without revealing a complete list of damaged components. With correct and careful diagnostics, in most cases everything ends well and the breakdown can be eliminated by replacing the damaged parts with the same serviceable ones or close in value and parameters.
Video instructions for repairing a switching power supply:
Switching power supplies are the most unreliable component in modern radio devices. This is understandable - huge currents, high voltages. The UPS passes all the power consumed by the device. At the same time, let's not forget that the amount of power supplied by the UPS to the load can change tens of times, which cannot have a beneficial effect on its operation.
Most manufacturers use simple schemes switching power supply, it is understandable. The presence of several levels of protection often only complicates the repair and practically does not affect the reliability, since the increase in reliability due to the additional protection loop is compensated by the unreliability of additional elements, and during repair it takes a long time to understand what these parts are and why they are needed.
Of course, each switching power supply has its own characteristics, which differ in the power supplied to the load, the stability of the output voltages, the operating range mains voltages and other parameters that play a role during repair only when you need to choose to replace a missing part.
It is clear that it is desirable to have a circuit during repairs. Well, if it is not there, simple TVs can be repaired without it. The principle of operation of all switching power supplies is practically the same, the only difference is in circuit solutions and types of parts used.
- How to fix ?
So, step-by-step instruction repair of a switching power supply:
- We turn on the TV, make sure that it does not work, that the standby indicator is off. If it is on, then most likely the matter is not in the power supply. Just in case, you will need to check the line scan supply voltage.
- We turn off the TV, disassemble it.
- We conduct an external examination of the TV board, especially the area where the power supply is located. Sometimes swollen capacitors, burnt resistors, and more can be found. It will be necessary to check them in the future.
- We carefully look at the soldering, especially the transformer, key transistor / microcircuit, chokes.
- We check the power circuit: we ring the power cord, fuse, power switch (if any), chokes in the power circuit, rectifier bridge. Often, when the UPS is faulty, the fuse does not burn out - it simply does not have time. If the key transistor breaks down, the ballast resistance will burn out rather than the fuse. It happens that the fuse burns due to a malfunction of the posistor, which controls the demagnetizing device (demagnetizing loop). Be sure to check the filter capacitor leads for a short circuit. mains supply, without soldering it, since in this way it is often possible to check for breakdown the conclusions of the collector - the emitter of the key transistor or microcircuit if a power switch is built into it. Sometimes power is supplied to the circuit from the filter capacitor through ballast resistors, and in case of breakage, it is necessary to check for breakdown directly on the key electrodes.
- We check the rest of the block details - diodes, transistors, some resistors. First, we check without unsoldering the part, we solder it only when there is a suspicion that the part may be faulty. In most cases, this check is sufficient. Ballast resistances are often cut off. Ballast resistors have a small value (tenths of Ohm, units of Ohm) and are designed to limit impulse currents, as well as for protection as fuses.
- We look for shorts in the secondary power circuits - for this we check for a short circuit the terminals of the capacitors of the corresponding filters at the outputs of the rectifiers.
We include. At this stage, three options are possible:
- The light bulb flashed brightly, then went out, a raster appeared. Or the standby indication came on. In both cases, it is necessary to measure the voltage supplying the horizontal scan - it is different for different TVs, but not more than 125 Volts. Often its value is written on the printed circuit board, sometimes near the rectifier, sometimes near the TDKS. If it is overestimated to 150-160 Volts, and the TV is in standby mode, then put it into working mode. In some TVs, it is allowed to overestimate the voltage at idle (when the line scan does not work). If the voltage is too high in operating mode, check the electrolytic capacitors in the power supply only by replacing it with a known good one. The fact is that often electrolytic capacitors in a UPS lose their frequency properties and at the generation frequency cease to perform their functions, despite the fact that when checked with a tester by the charge-discharge method, the capacitor seems to be working properly. The optocoupler (if any) or the optocoupler control circuit may also be faulty. Check if the output voltage is internally regulated (if any). If it is not regulated, then you must continue to search for faulty parts.
- The bulb flashed brightly and went out. Neither a raster nor an indication of the standby mode appeared. This indicates that the switching power supply does not start. It is necessary to measure the voltage across the capacitor of the mains filter, it should be 280-300 Volts. If it is not there, sometimes they put a ballast resistance between the bridge of the mains rectifier and the capacitor. Check the supply and rectifier circuits again. If the voltage is too low, one of the diodes of the mains rectifier bridge may be cut off or, more often, the capacitor of the mains supply filter has lost its capacity. If the voltage is normal, then you need to check the rectifiers of the secondary power supplies, as well as the starting circuit. The trigger circuit for simple TVs consists of several resistors in series. When testing a circuit, you need to measure the voltage drop across each of them, measuring the voltage directly at the terminals of each resistor.
- The light is on at full brightness. Switch off the TV immediately. Check all items again. And remember - there are no miracles in radio engineering, it means that you missed something somewhere, did not check everything.
- Step by step
In the modern world, the development and obsolescence of personal computer components occurs very quickly. At the same time, one of the main components of a PC - the ATX form factor - is practically has not changed its design for the last 15 years.
Consequently, the power supply unit of both the ultra-modern gaming computer and the old office PC work on the same principle, have common troubleshooting techniques.
The material presented in this article can be applied to any power supply for personal computers with a minimum of nuance.
A typical ATX power supply circuit is shown in the figure. Structurally, it is a classic pulse unit on the 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 to ground, only the Standby Supply with a voltage of +5 V at the output is active.
Let's consider the structure of the ATX power supply in more detail. Its first element is
:
Its task is to convert AC from the mains to DC 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 overloading in the event of a power supply 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 power supply unit is connected to the network.
- Next, a noise filter is installed, consisting of several chokes ( L1, L2), capacitors ( C1, C2, C3, C4) and a counter-winding choke Tr1... The need for such a filter is due to the significant level of interference that the impulse unit transmits to the power supply network - this interference is not only captured 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 pulsating direct current. The ripple is smoothed out by a capacitive-inductive filter.
Standby power supply Is a low-power independent switching converter based on the T11 transistor, which generates pulses, through an isolation transformer and a half-wave rectifier on the D24 diode, supplying a low-power integrated voltage regulator on the 7805 microcircuit. high voltage drop across the 7805 regulator, which under heavy load leads to overheating. For this reason, damage in the circuits powered from the standby source can lead to its failure and the subsequent impossibility of turning 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, the change in the duration of voltage pulses at their constant amplitude and frequency. The task of the PWM unit, based on the specialized TL494 microcircuit or its functional analogs, is to convert the constant voltage into pulses of the corresponding frequency, which, after the isolation transformer, are smoothed by the 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.
The reason for the failure of the power supply, or why the technique stops working. Recently, I began to notice more and more often that people began to turn, and I myself find myself, for a strange and monotonous repair of equipment. Everything starts in approximately one scenario - the device worked for a year or two and then suddenly it started to turn on slowly, or not at all, or when turned on, it turns off abruptly, or it tries to turn on but does not turn on! In general, we take a tester and measure the voltage on it, more precisely at the output terminals, it is usually within acceptable limits, or, alternatively, it differs by 0.3-0.4 volts downward, for example, for 12 volt power supplies, it is usually 11.4 volts.
But if you check with an oscilloscope, or a simple tester from a speaker, then high-frequency ripples are heard, therefore, without smoothing, this equipment with such a power supply cannot work!
Such capacitors, as a rule, externally noticeably swell on the lid or explode altogether, during testing they may show a noticeable decrease in capacitance - instead of 1000 microfarads, there will be 120-150 microfarads, or even less, or in the tester the capacitor may be defined as another element altogether.
With such a miracle, when the capacitor suddenly becomes a resistor or a diode, the power supply tries to turn on, but the currents become high and in large branded TVs such units go into protection. With a new attempt to turn on everything is repeated in a circle ...
Often, replacing the filter capacitor can be done with an increased capacity, for example, instead of a battery of three capacitors of a rare capacity of 1500 microfarads, you can put it in 4000 microfarads. The main thing is to check then the stability of the device and the level of ripple, so that everything is normal, and so that the capacitor is at the required voltage, or better with a voltage margin, then it will be additionally protected from surges.
Problems and defects in power supplies can be completely different - from complete non-operability to permanent or temporary failures. As soon as you start repairing the power supply, make sure that all contacts and radio elements are visually in order, the power cords are not damaged, the fuse and switch are working, there are no short circuits to ground. Of course, the power supplies of modern equipment, although they have general principles of operation, are quite different in circuitry. Try to find a diagram for the power supply, this will greatly simplify and speed up the repair, remember that many power supply diagrams with a list of typical faults can be found in the service manual for this equipment.
When starting a repair, you must be able to use a multimeter, and preferably an oscilloscope, and, of course, have tin and rosin.
The problematic power supply becomes the cause of the unstable operation of the device, manifesting itself either as periodic errors in operation, or spontaneous glitches, or even the output of one or another node in the equipment.
At the first signs of unstable operation of the power supply, it is necessary to start repairing and diagnosing the power supply as soon as possible. And the first action that you must take immediately after opening the device case is to vacuum the power supply, and then carefully inspect all radio components and their connections.
Inspect all electrolytic capacitors carefully for swollen capacitors. And the best thing is if you check each of them. Even if the capacitor looks great, this does not mean that it has not lost capacity or its ESR has not dramatically increased. There are small attachments for multimeters and ready-made ones that will help even without soldering it out of the circuit. If you wish, you can assemble such a device yourself.
Another problem that may arise and require repair of the power supply is unstable operation and ripple of the supply voltage caused by poor filtering. They are easy to see on the oscilloscope screen. Small pulsations can be ignored, and with strong noises, repairs will be required. But the issue of ripple is acute only in switching power supplies used in TVs, monitors, computers and is not at all relevant for any simple devices.
Let's consider the different types of power supplies and the problems that arise in them in more detail.
Switching power supplies are the most unreliable element in modern household appliances and devices. This is also logical - high currents, high voltages - after all, all the power that the circuit consumes passes through the pulsed power supply unit. At the same time, keep in mind that the power supplied by the power supply to the load can change dozens of times during operation, which is not very good in itself.
Most firms use simple switching power supply circuits. It is understandable, firstly, it is cheaper, and secondly, there is a high probability that your device will fail after several years of operation.
When repairing a switching power supply, it is advisable to have a circuit. Well, if it is not there, simple TVs can be repaired without it. The principle of operation of all pulse generators is practically the same, the only difference is in circuit solutions and types of parts used. Huge monitors and video equipment you can download from us.
Getting started repairing the power supply using the example of a UPS from a TV.
Turn on the TV, make sure that it does not turn on, that the standby LED is off. If it is on, then the problem is most likely not in the PSU.
Turn off the TV, disassemble it
Visual inspection of the board, especially the place where the impulse power supply is located
Carefully inspect the soldering points, especially at the transformer
Ring the power cord, fuse, power switch, chokes and rectifier bridge. Then, diodes and zener diodes and, if possible, microcircuits. First, carry out the check without unsoldering the radio component from the circuit, unsolder only when you suspect it.
Often, when a pulsed power supply unit breaks down, the fuse does not have time to burn out. In the case of a burnt out key transistor, check the ballast resistance as well. Fuse due, which is used in CRT TVs to control the demagnetizing device. Be sure to ring the terminals of the mains power filter capacitor for a short circuit with a multimeter, but do not unsolder it from the circuit, since you can also check a key transistor or a microcircuit with a built-in power switch for a breakdown.
Ballast resistances are often cut off. Since they have very low resistance (tenths of Ohm, units of Ohm) and are used to limit impulse currents, as well as for protection
It is necessary to see if there are any short circuits in the secondary power circuits - for this we check for a short circuit the terminals of the capacitors of the corresponding filters at the outputs of the rectifiers
After completing all these points and replacing defective parts, you can carry out a live test. But before mixing the mains fuse, install a 150-200 Watt bulb (or series-connected bulbs). The load will protect your switching power supply if the problem persists.
There are three options:
The light bulb lights up brightly, and then goes out, a raster appears. Or the standby LED comes on. It is necessary to measure the voltage of the drain sweep. If it is too high, check the electrolytic capacitors, but only by replacing them with an exactly serviceable one. Also, optocouplers (if they are present in the circuit) or its control circuit may not work. can be read here.
If the light bulb flashed brightly and went out. Raster, no indication. This means that the pulsed power supply unit does not start. It is necessary to measure the voltage on the capacitor of the mains filter and make sure that it is about 280-300 Volts. If not, ring the power circuit and rectifier again. If it is lower, check the diode bridge or there has been a loss of capacity in the filter capacitor. If the voltage corresponds to 280-300 volts, check the rectifiers of the secondary power supplies, as well as their starting circuits.
The light is very bright. Unplug the TV immediately. Check everything again
Usually, defects that arise in switching power supplies fall into this troubleshooting algorithm, but sometimes more complex problems are encountered. There is no method for such cases, just turn on your brains.
Let's estimate the possible options for why the power supply can burn out and what problems can there be for the rest of the electronics of the system unit? Very often, the blocks burn with voltage surges, in this case, first of all, you need to ring the input circuits of the inverter or filter, sometimes damaged elements can be recognized just by visual inspection.
If the ATX power supply in a personal computer does not show signs of operability: the fans do not spin, the motherboard does not start, turn off and remove it from the system unit for repair.
So, before you start repairing the power supply, you need to understand exactly that the computer does not work only because of it. Only then can you start removing the power supply from the case. For those who do it for the first time, I recommend taking a picture of their connection before disconnecting the cables from the motherboard.
In order to be able to turn on the computer power supply for repair purposes you need to connect a load to it according to the diagram:
In the absence of traces of burning and other noticeable malfunctions. We start repairs from fuse checks... If it is burned out, connect an incandescent lamp of 100 watts to it, as in the case of repairing a pulsed TV power supply. If there is a short circuit, it will flash brightly, and thereby signal us about the breakdown of the diode bridge or capacitors.
Now you need to check all the output voltages of the PSU.
To test the +/- 5 V and +/- 12 V circuits, measure their resistance with the power supply turned off (+5 V is red, and +12 is yellow, black is ground). If the resistance is less than 100 Ohm, most likely, there has been a breakdown of the diodes in the rectifier bridge. Breakdown of rectifier diodes is most often manifested by a quiet buzzing. Check the -5 V / -12 V lines in the same way.
More difficult make sure that the PWM controller is working on the TL493 chip, TL494, TL495. Their data and pinout are available in. Start by measuring the supply voltage of the IC. If this voltage is absent, check the external circuits and, provided that they are in order, replace the microcircuit.
Use a multimeter to measure the reference voltage on the microcircuit, it should be +5 V. If the voltage does not match, check the resistor dividers connected to this circuit.
On pin 5 of TL493, TL494, TL495 there should be a sawtooth voltage ripple with an amplitude of about 3 V and a frequency of 1 to 50 kHz, which can be viewed with an oscilloscope. If they are not there, check the capacitor at the 5th leg, and the resistor 6. If they are serviceable, change the microcircuit.
It remains to check the signals at the output of the PWM controller. If there are pulses with clear edges and an amplitude of the order of 2-3 V, the microcircuit is in good order. Otherwise, transistors in the high-voltage switch circuit are broken.
Also, it will not be superfluous to check the transformer windings.
There is also such a typical defect: The computer power supply turns on by itself. The fans are running and the computer won't turn on. The cause of the defect, in most cases, is the breakdown of the standby voltage regulator of the power supply, which forms the standby voltage of + 5V. Without seeing it at startup, the system is simply not able to pass the initial stage of self-testing.
If you broke in to assemble the load circuit, then you can simply close the PS-ON and COM contacts. The figure below shows two versions of the pin locations on the ribbon computer unit nutrition.
But before you close the PS-ON and COM contacts with each other, you need to check for the presence of a “standby” voltage of + 5V on the “+ 5VSB” contact, which is usually purple. To do this, you need to turn on the power supply unit to the 220 volt network, take a multimeter, switch it to the "voltmeter" mode, then connect the negative probe to one of the COM contacts, and connect the positive probe to + 5VSB. The multimeter should show the presence of + 5V. If there is no voltage, then it is necessary to disassemble the power supply unit and check the circuit for this power supply.
If there is a "standby" voltage, then you can safely bridge the PS-ON and COM contacts, and after applying 220V power, proceed to check the remaining available voltages.
If the absence of one or more of them is revealed, then you can start disassembling the supply source.
After disassembling, first of all, clean the PSU from dust. After cleaning, visually inspect the board, especially the capacitors, they love to swell up there. It looks like this:
If you find such capacitors with swollen tops, feel free to change them. This malfunction is the most common, and almost everyone who knows how to hold a soldering iron with their hands, and not their branches from one place, can eliminate such a minor nuisance. Most importantly, do not forget that all electrolytic capacitors have polarity, so do not confuse their outputs.
Repair of power supplies - Zalman ZM500-GS with a malfunction does not turn on.
Having connected the power supply unit to the network and checked it with a tester for computer power supply units, I was convinced of its complete inoperability. The mains fuse is blown. By connecting a 100 watt incandescent lamp instead. In working condition under load, it should light up (at the time of charging the network capacities), and then dim a little. In standby mode, when the power supply consumption is low, the lamp may glow for a short time, after which it goes out. This behavior should be repeated cyclically.
After turning on the power, the lamp lit up brightly, indicating a short circuit or a large current consumption in the primary circuits. Having connected the tester, I made sure that all the output voltages were present at the ATX connector. This is already buzzing, tearing off the thermal insulation from a radio element similar to a capacitor, I saw burnt under it. Replacing it with a new power supply unit began to work correctly.
They gave me a Chinese transformer power supply, model HKA-12100EC-230, but it turned out to be not working. If you believe the designation on it, it gives out a current of up to 1 A. This is exactly what I need, so I decided to disassemble and try to repair this Chinese.
An educational film in Russian, revealing the technology of repairing a computer ATX power supply
Very often my clients contact me with a problem that the power supply unit on any device does not work. Power supplies I divide it into two categories: "simple" and "complex". To "simple" I include antennas, power supplies from any game consoles, from portable TVs and others like that, which are directly plugged into the outlet. In a word - remote, i.e. separate from the main unit. The “complex” ones in my distribution scheme are the power supplies that are in the device itself. Well, we will leave “complicated” alone for now, but let's talk about “simple” ones.
There are not many reasons for remote control failure. power supplies... I will list them all:
Open circuit in the transformer windings (primary and secondary);
Short circuit in the transformer windings;
Failure of the voltage rectifier (diode bridge, capacitor, stabilizer and associated radio elements).
If, when the unit breaks down, there are no voltages at its output at all, then most likely the reason is in the transformer. If there is an underestimated voltage at the output, then the matter is in the rectifiers. You can check the transformer by measuring the resistance on its windings. On the primary winding, the resistance should be more than 1 kOhm, on the secondary or secondary - less than 1 kOhm. In some power supplies, on the primary winding, under the wrapping, which the winding itself wraps around, a fuse is placed. To get to it, you need to break the wrapper on this winding. Most often, such a protection mechanism is present in Chinese-made transformers. So if the primary winding does not ring out, then check if a fuse may be installed on it.
With the transformer sorted out. Now let's move on to checking the voltage rectifier and its components. The most common failure in power supplies is the failure of one or more elements, of which the voltage rectifier actually consists. These are the reasons we will discuss with you in this article. We will produce dIY power supply repair.
Consider this using the example of an antenna power supply with output voltage 12 in.
On this power supply unit, the output voltage is too low: instead of the prescribed 12 Volts, it outputs 10 Volt... So let's get down to fixing this problem. First, of course, you need to disassemble the block itself. After we make sure that the transformer in this device is intact, we proceed to check the rectifier elements.
First of all, we check the diode bridge - these are four diodes to which the contacts from the secondary winding of the transformer go. I told how to check diodes in the video that you will find at the end of this article. In our block, the diode bridge is intact. Now we look at a capacitor: it happens that capacitors "swell". Our capacitor is not "swollen". If the diode bridge and capacitors are intact, we inspect the rectifier board for blackening or burning of the elements on the board.
If everything is visually in order, then feel free to solder the voltage stabilizer. This rectifier has a voltage stabilizer 12 Volts - 78L12. Almost always, it is this element that fails. Before removing this part from the board, remember how this part was installed on the board, so as not to reverse the polarity when replacing. Together with the stabilizer, I also recommend replacing the capacitor, this is for reliability, since most often it also fails.
After replacing these parts, check if the wires coming from the transformer have been unsoldered during the repair process.
If all is well, we collect ours. Measurements made after our repair of this power supply showed the output voltage 12 Volts, which, in general, we needed. All!
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