DIY LED repair

In detail: DIY repair of LEDs from a real master for the site my.housecope.com.

A decade ago, such a rapid growth in the popularity of LED lighting for apartments and private houses was not expected. Today you will not meet a person who would not use these economical and bright lamps. The only problem remains in the cost of lighting fixtures - such fixtures cannot be called cheap. What if the lamp is out of order? Buy a new one? Not necessary. You can try to repair the lighting fixture. It is precisely the "device", because it is a complex technical device, in contrast to the "Ilyich's lamp". Today we will figure out how to repair LED lamps with our own hands and how difficult it is.

LEDs are the most economical type of lighting - it's hard to argue with that. Such elements are used both in everyday life and in production. Street lighting is gradually moving towards similar energy savings. Light diodes, in addition to efficiency, have another indisputable advantage over other types of lighting devices - they have no competitors in terms of durability. But they cannot work directly from a network with an alternating current of 220 V. This requires a special device called a driver.

The circuit of a 220 V LED lamp includes a device that is compact enough and fits in the base. There is nothing more complicated in the lighting device, however, the driver, performing work to stabilize the voltage, often fails. Burnt-out LEDs are not difficult to replace, it is enough to own a soldering iron at the "just learned" level. But today we will figure out how to repair drivers.

Video (click to play).

The general principle of operation of LED lamps is as follows. The alternating current of the network enters an electronic device - a driver that stabilizes voltage drops. Direct current is directed to LEDs, which emit the light we see.

Related article:

How to choose LED bulbs for your home. In this material, we will consider the device of light semiconductors, their varieties, average prices, manufacturers, selection criteria, room illumination standards, expert advice, and find out why the lamps are blinking.

If we simplify such a system, we get a 220 V LED lamp driver circuit, which includes two damping resistors that stabilize the voltage. LEDs are connected in different directions, which protects against reverse voltage. The flicker frequency doubles - from 50 to 100 Hz.

Power in such a circuit is fed through a limiting capacitor to a rectifier (diode bridge), and only then to the elements. We simplify the system. We change one light diode to a rectifier. The lamp works, but the frequency of the current, instead of increasing, decreases by 2 times and becomes equal to 25 Hz, which leads to a sensitive flickering of the lighting fixture. It is harmful to vision, impairs health, increases fatigue and causes headaches.

However, there are LED lamps at a completely different cost. For example, GENILED SDL-KS 80W 07077, 80 W power and 4700K color temperature. Its cost can be surprising. It is equal to 10,200 rubles.

Often the reason for the failure of an LED lamp is improper operation or sudden voltage drops in the network. Let's take a look at the most common ones:

A sharp power surge. LEDs in such a situation will remain intact, but the driver may fail;
Wrong choice of luminaire. If normal ventilation is not provided, the driver overheats, which negatively affects its operation;
Factory defect or falsification of products. If you come across a too cheap lamp of this type on the counter, you should think about how the low price was achieved;
Vibration and shock. They are not terrible for LEDs, but for the driver they can be fatal.

Most often, the capacitor fails (the lamp will stop burning), and the current-limiting resistor (sensitive flickering, up to blinking). In order not to buy new equipment, you need to understand how to repair an LED lamp with your own hands.

Colored LEDs create a unique ambience in the room

The driver, which causes failure in 80% of cases, is not necessarily built into the light bulb. The light source can only consist of LEDs, and the stabilizing device will be built into the lamp or chandelier. However, the remaining 20% should not be discounted. It is necessary to check all the details before proceeding with the repair of the ice lamps.

In the case of a separate driver, everything is simpler. We change the lamp, and if it glows, then the problem is in it, if not, the stabilizer is to blame. The situation with the built-in driver is more complicated.

Now the promised secret. To repair LED lamps with an ordinary soldering iron, you need a piece of copper single-core wire, with a cross section of 4 mm², 10 ÷ 15 cm long. "Scapula". The temperature will also depend on the length. Convenient if the multimeter has a thermometer function. For LED SMD components, which are used in LED lamps, a temperature of 240 ÷ 260 ° C is required.

You can put a jumper here - quickly, but not for long

Some devices are not easy to disassemble. When you try to rotate the top, nothing comes out? Then a solvent comes in handy. We put it into a syringe and carefully pass through the needle along the seam. We leave for 5 minutes, after which we repeat the operation. Usually 2 ÷ 3 procedures are enough. Gently swing the upper part by turning left and right. After removing the cover, we clean off the old sealant and degrease the surfaces. If you plan to use the lamp in a dry environment, you do not need to apply new sealant.

It is not difficult to disassemble the LED lamp, the main thing is that the benefits are

Having figured out how to fix a 220V LED lamp, it makes sense to deal with more complex devices, such as spotlights or chandeliers. Although there is not much difference in the work. Experts say that repairing LED floodlights is even easier, because the drivers and their parts are larger. We subscribe to this opinion. It only seems that such devices are more high-tech and more complex. In fact, having diagrams at hand (they are always contained in the technical documentation of a lighting device), for example, repairing an LED chandelier is quite simple. The same continuity of LEDs, driver details. After - the selection of suitable ones to replace the burned ones.

Important information! If the LED burns out and there is no suitable replacement at hand, you can slightly extend the life of the lighting device. The contacts of the burned-out element are bridged among themselves, and the lamp lights up again. But you should be prepared for the fact that after a short time it will go out again. The LED next to the bridged one will light up. If you continue to install the jumpers, the time between repairs will decrease exponentially.

Several LED lamps will transform the interior beyond recognition, but for the better.

If all the LED lighting in the bathroom goes out at the same time, you should start small. Remove the switch cover and check the voltage supply. If everything is in order, then the problem is in the power supply.

A bathroom is a room with high humidity, in which the use of 220 volt lighting fixtures is unacceptable. For this reason, a 12 volt power supply is installed.The reason that all the lighting stopped burning at once may be the failure of this device or a breakdown of the wiring, which is hardly realistic. You will have to buy such a block. Having dismantled the old block, we look at the technical parameters, purchase a stabilizer with similar characteristics and install it in place.

When working with electrical wiring, you need to be extremely careful. Defeat is dangerous

Important! All work on dismantling and installation of the stabilizing power supply is carried out only with the voltage removed. It is better to turn off the introductory machine. This is the only way to protect yourself from electric shock.

This is a common problem. It happens that people refuse to replace ordinary lighting in an apartment with LED due to the fact that when the light is off, the LEDs blink, in the manner of a stroboscope. There is only one reason for this - the backlight of the switch.

If the indicator is on, it is passing a certain amount of electricity through it, which does not have any effect on conventional lamps. But in the driver of LED lighting devices there is a capacitor that has the ability to store electricity and then give it out. He then collects this energy "bit by bit", and upon reaching a certain volume gives it in the form of a pulse to the LEDs.

This indicator causes the LEDs to blink.

The problem can be solved very simply - turn off the backlight on the switch. However, blinking due to the indication on the key is a consequence. And what's the reason? There are also no difficulties here. The reason is the incorrect connection of the chandelier sockets. It is known that when incandescent lamps are installed, zero goes to the thread of the base, and the phase goes to the center. The LEDs start blinking if this order is violated and the wiring is done incorrectly.

Filament lamps are new to the market. They cannot be repaired.

LED lighting continues to grow in popularity. But even with a decrease in prices for lighting devices based on them, they remain expensive. And why overpay if you can repair a light bulb or lamp with your own hands. You don't even need to purchase parts for this. You just don’t need to throw out those that are out of order. Then from two or three it will be possible to collect one worker.

We hope the information presented in our article will help the reader to save money on the purchase of lighting equipment. If you have any questions, you can ask them in the discussion below. And finally, we suggest watching a useful video on the topic:

Before proceeding with the repair of a 220 or 12 volt light bulb, you need to familiarize yourself with its device. As mentioned above, the design is extremely simple. The lamp can be conditionally divided into three parts: a body with a base and a light filter, a power supply board for LEDs, and an LED module.

Having carefully disassembled the case, the insides of the electronic circuit will open in front of you. Most of the Chinese manufacturers of inexpensive devices such as corn and similar LED light emitters install transformerless capacitor current sources. In these circuits, the capacitor acts as a current and voltage limiter.

For the information of the reader, we will say that the operating voltage of one LED is 3.3 Volts, and the current of the semiconductor crystal is about 20-50 μA, depending on the type of diode. If these parameters are overestimated, the diode will overheat and the crystal will break through and fail.

How LED bulbs work. Sequentially in a chain of 50-60 LEDs are soldered together, together forming a light-emitting element for a voltage of 180 volts. A power capacitor with a resistor limits the current and voltage to the required level.

Often, manufacturers of such devices are deliberately deceiving, and this is what: if you increase the current through the crystal above the operating rating, but within reasonable limits, then the radiation from the diode will increase.In this regard, the heat generation will also become higher, with which you can fight for a short time. This trick favorably distinguishes them from competitors, due to the higher brightness with the same declared power. However, it results in a drop in light emission or destruction over time and bitter disappointment for the user.

So, having an idea of \ u200b \ u200bthe electronic circuitry of our LED lamp that does not work, we will consider how to repair it at home.

First of all, we make a visual inspection of the microcircuit and the diodes themselves. In 80% of cases, a burned-out LED is a breakdown. To carry out repairs, you first need to find a diode that visually differs from the rest, for example, by the presence of a pronounced black point, as shown in the photo below, and then replace it with a new one.

Video tutorial on repairing an LED light bulb in which an LED burned out:

The current limiting resistor may also burn out. Working capacitors rarely fail, breaking down the remaining elements of the LED device.

Once you are studying this page, we hope that you have a soldering iron and a basic understanding of electronics. Now about the troubleshooting technique. The diode can be checked both with a multimeter and with a crown with a 1 kOhm limiting resistor. By alternately placing the wiring on the leads of the LED, the serviceable one will shine. A multimeter in the dial position will also make the LED light up, subject to polarity.

If no problem is identified with the light emitter, we check the limiting resistor with a tester, in most circuits its nominal value is about 100-200 ohms. We recommend watching more complex repairs in the video:

Also, the scourge of modern circuits is such a thing as "cold soldering". This is when, over time, contact breaks down in a poorly filled tin soldering point.

The circuit breaks down physically and breaks the integrity of the circuit, with the result that the LED lamp will not turn on. The breakdown can be repaired by reheating the place of contact with the application of flux to it.

Rare faults are rectifier diode or capacitor breakdown that occurs during power surges. With the help of a tester, you can establish this thoroughly. Having identified the cause and replacing the burnt out element, you can return the lamps to working condition. You can learn more about how to check a capacitor in our related article.

In more expensive LED devices, instead of a capacitor power supply, there is a switching power supply that automatically adjusts to the voltage in the network, and by adjusting it, it keeps a constant voltage and current at the output, preventing the diode crystals from overheating, providing a long service life and a constant luminous flux.

The troubleshooting method practically does not differ from the above, and most likely it will be cold soldering on any of the elements. In this case, repairing an LED lamp will not be difficult.

If the diode lamp does not light up or flickers, it is far from always the reason for its malfunction. In most cases, the blinking is due to the fact that it is connected to a backlit switch. In this case, the problem can be solved by replacing the switch with a conventional one. Also, as a repair, you can consider another simple way to fix the problem - turn off the backlight on the switch by disconnecting the diode bulb in it.

However, sometimes the lamp may still blink because something came off in it, for example, the wire from the base was sealed off. In this case, it is quite simple to repair it using the following technology:

After reading our article, you may have such a question, is it possible to assemble such a light source yourself? You can, this is exactly what I did, before I started using factory LEDs, and then because of the specifics of the chandelier and design.Using an LED strip and a reworked electronic transformer, a desktop lamp was made with two modes of operation. Later, a night light was made on one powerful three-volt diode and a decorative sconce made of twine.

You can also learn how to make an LED light bulb in our separate publication. We hope you are interested in this article, not only with the possibility of repairing an LED lamp with your own hands, but also with the idea of creating beautiful and unusual light sources!

author

Dmitry Melekhin 11.01.2018, 09:28 2.8k Views 0 Opinions

Light sources of this category are in great demand on the modern market. They consume a small amount of energy, are durable and resistant to various external influences. However, any technical device can fail during operation. A factory defect, which may appear after the end of the official warranty period, cannot be ruled out. Do-it-yourself qualified repair of LED lamps will help to fix the problem at no extra cost. This article provides technologies for restoring device operability at home with step-by-step instructions and explanations.

It should be noted right away that lamps with such LEDs (filament) cannot be repaired. In them, the flask is filled with an inert gas, and the manufacturers keep the exact composition secret. High-quality reproduction of industrial technology at home is impossible.

They are all made from standard, inexpensive LEDs that can be purchased easily. Typical tools are suitable for checking and performing work operations. The simplest special devices for dismantling and subsequent assembly can be made by hand.

It makes no sense to study physical processes in detail. Suffice it to say that in this case the light source is a specialized semiconductor device. It emits light when applied to a constant voltage of several volts at a relatively low current strength. This means that rectification and limitation of the corresponding electrical parameters will be required. The presence of a p-n junction indicates the possibility of clarifying the operability using a typical test of a conventional diode.

A driver is an electronic circuit that rectifies the voltage, limits the current to its nominal value. The required number of LEDs is installed on a substrate with a heat sink for heat dissipation. The diffuser eliminates irregularities in the luminous flux and excessive brightness of individual emitting elements.

In this simplest 220V LED lamp driver circuitry, capacitor C1 together with resistor R1 reduce the voltage to the desired value. It is determined by the number of LEDs connected in series. On each of them, the voltage drop is about 3 V (the exact value is indicated in the technical data sheet of the device). After the diode bridge, the remaining ripple is smoothed out by the capacitor C2. Resistors R3, R4 limit the inrush current when connected to the power supply. When the lamp turns off, the parallel capacitor is quickly discharged through R2.

In the circuit under consideration, the simplest electronic components are used that rarely fail. According to statistics, the most often damaged electrolytic smoothing capacitor. Problems arise if parts are used "sparingly" without a voltage margin.

Insufficient quality soldered joints are also encountered. They are destroyed after several on / off cycles as a result of thermal expansion / contraction. Repair of LED lamps may be needed more often if they are installed in a room with high humidity. In lamps of this type, there are no contact groups that are damaged by the formation of a film of oxides. Therefore, here, too, the cause of breakdown will be defective soldering.

Sometimes heat dissipation is poorly organized.Under such conditions, LEDs are unable to perform their functions for a long time. It is unacceptable if a plastic fake is installed instead of a metal radiator. It makes sense to repair such products only with a complete replacement of unusable parts of the structure. In case of incompetent assembly, they "save" thermal paste or do not use it at all. In this case, even a high-quality aluminum radiator will not perform its functions with maximum efficiency.

To eliminate doubts, check 220 V directly in the cartridge. To do this, use a multimeter, a phase probe (a screwdriver with a built-in phase indicator), or screw in another workable lamp.

With a variety of lighting devices on the counters of the country, LEDs remain out of competition due to their efficiency and durability. However, a high-quality product is not always purchased, because in a store you cannot disassemble the goods for inspection. And in this case, it is not a fact that everyone will determine from what parts it is assembled. Lamps burn out, and it becomes expensive to buy new ones. The solution is to repair LED lamps with your own hands. This work is within the power of even a novice home craftsman, and the details are inexpensive. Today we will figure out how to check the lighting device, in what cases the product is repaired and how to do it.

LED lighting products have become part of our lives

It is known that LEDs cannot work directly from a 220 V network. To do this, they need additional equipment, which, most often, fails. We will talk about him today. Consider the circuit of an LED driver, without which the operation of the lighting device is impossible. Along the way, we will conduct an educational program for those who do not understand anything in electronics.

The 220V LED lamp driver circuit consists of:

diode bridge;
resistances;
resistors.

The diode bridge serves to rectify the current (converting it from alternating to direct current). On the graph, this looks like a cut-off of a half-wave of a sine wave. Resistances limit current, and capacitors store energy by increasing the frequency. Consider the principle of operation on the circuit of a 220 V LED lamp.

Having understood the principle of operation and the driver circuit, the decision on how to fix a 220V LED lamp will no longer seem difficult. If we talk about high-quality lighting devices, then you should not expect trouble from them. They work for the entire prescribed period and do not fade, although there are "diseases" to which they are also susceptible. Let's talk about how to deal with them.

To make it easier to understand the reasons, we summarize all the data in one common table.

Good to know! Repair of LED fixtures is impossible to carry out indefinitely. It is much easier to eliminate negative factors affecting durability and not to purchase cheap products. Savings today will cost you tomorrow. As economist Adam Smith said, "I'm not rich enough to buy cheap things."

Before you repair an LED lamp with your own hands, pay attention to some details that require less labor. Checking the cartridge and the voltage in it is the first thing to do.

Important! Repair of LED lamps requires a multimeter - without it, it will not be possible to ring the driver elements. A soldering station is also required.

A soldering station is required for the repair of LED chandeliers and lighting fixtures. After all, overheating of their elements leads to failure. The heating temperature during soldering should be no higher than 2600, while the soldering iron heats up more. But there is a way out. We use a piece of copper core with a cross section of 4 mm, which is wound around the tip of the soldering iron with a tight spiral. The more you lengthen the sting, the lower its temperature. Convenient if the multimeter has a thermometer function. In this case, it can be adjusted more precisely.

But before you repair LED spotlights, chandeliers or lamps, you need to determine the cause of the failure.

One of the problems that a novice home craftsman faces is how to disassemble an LED light bulb. To do this, you need an awl, solvent and a syringe with a needle. The diffuser of the LED lamp is glued to the body with a sealant that must be removed. Passing carefully along the edge of the diffuser with an awl, inject the solvent with a syringe. After 2 ÷ 3 minutes, lightly twisting, the diffuser is removed.

Checking the disassembled LED bulb. You shouldn't do this - it's dangerous.

Some lighting fixtures are made without gluing with a sealant. In this case, it is enough to turn the diffuser and remove it from the housing.

Having disassembled the lighting fixture, pay attention to the LED elements. Burned is often identified visually: there are burn marks or black dots on it. Then we change the faulty part and check the functionality. We will describe the replacement in detail in the step-by-step instructions.

If the LED elements are in order, go to the driver. To check the performance of its parts, you need to solder them from the printed circuit board. The value of the resistors (resistances) is indicated on the board, and the parameters of the capacitor are indicated on the case. When dialing with a multimeter in the appropriate modes, there should be no deviations. However, often failed capacitors are determined visually - they swell or burst. The solution is to replace it with a suitable one in terms of technical parameters.

The LED can be ringed with a multimeter without unsoldering from the printed circuit board

Replacing capacitors and resistances, unlike LEDs, is often performed with a conventional soldering iron. In this case, you should be careful not to overheat the nearest contacts and elements.

If you have a soldering station or a hair dryer, this job is simple. It is more difficult to work with a soldering iron, but it is also possible.

Good to know! If there are no working LED elements at hand, you can install a jumper instead of the burnt one. Such a lamp will not work for a long time, but it will be possible to win some time. However, such repairs are made only if the number of elements is more than six. Otherwise, the day is the maximum work of the repair product.

Modern lamps run on SMD LED elements that can be soldered out of an LED strip. But it is worth choosing those that are suitable for technical characteristics. If there are none, it is better to change everything.

Chinese driver - these guys love minimalism

Related article:

For the correct choice of LED devices, you need to know not only the general LED characteristics... Information about modern models, electrical circuits of working devices will come in handy. In this article, you will find answers to these and other practical questions.

If the driver consists of smaller SMD components, use a copper wire soldering iron on the tip. A visual inspection revealed a burnt element - we solder it and select the one that matches the marking. No visible damage is more difficult. We'll have to solder all the details and ring them separately. Having found the burnt one, we change it to a workable one and mount the elements in place. It is convenient to use tweezers for this.

Useful advice! Do not remove all elements from the PCB at the same time. They are similar in appearance, you can later confuse the location. It is better to solder the elements one at a time and, after checking, mount them in place.

Repairing an LED tube in the form of a fluorescent lamp is no different from working with a simple

When installing lighting in rooms with high humidity (bathroom or kitchen), stabilizing power supplies are used, which lower the voltage to a safe one (12 or 24 volts). The stabilizer can fail for several reasons. The main ones are excessive load (power consumption of the luminaires) or the wrong choice of the degree of protection of the unit. Such devices are repaired in specialized services. At home, this is unrealistic without the availability of equipment and knowledge in the field of radio electronics. In this case, the power supply unit will have to be replaced.

The power supply for the LEDs looks like this

Very important! All work on replacing the stabilizing LED power supply is carried out with the voltage removed. Do not rely on the switch - it may be incorrectly wired. The voltage is disconnected in the distribution board of the apartment. Remember that touching live parts with your hand is life-threatening.

You need to pay attention to the technical characteristics of the device - the power must exceed the parameters of the lamps that are powered from it. Having disconnected the failed unit, we connect a new one according to the diagram. It can be found in the technical documentation of the device. This is not difficult - all wires are color-coded, and the contacts are letter designation.

Decoding of IP protection degrees for electrical appliances

Plays the role and degree of protection of the device (IP). For a bathroom, the device must be marked at least IP45.

Related article:

In order for the lighting to be stable, and the installed products to serve as long as possible, you should choose the right 12V power supply for LED strip... In this publication, we will consider the types of devices, how to calculate them correctly, how to do it yourself, how to connect, popular models.

If the reason for the flickering of the LED lamp is the failure of the capacitor (it needs to be replaced), then periodic blinking when the light is off is easier to solve. The reason for this "behavior" of the luminaire is the backlight-indicator on the switch key.

The capacitor located in the driver circuit accumulates voltage, and when the limit is reached, it gives out a discharge. The key backlight transmits a small amount of electricity, which does not in any way affect incandescent bulbs or "halogens", but this voltage is enough for the capacitor to start accumulating it. At a certain moment, it gives out a discharge to the LEDs, after which it switches back to accumulation. There are two ways to solve this problem:

We take out the key from the switch and turn off the backlight. The method is simple, but indications that add value to the switch are no longer useful.
We disassemble the chandelier and change the phase wire with zero places on each cartridge. The method is more complicated, but it retains the functionality of the switch. In the dark, you can see it well, and this is a plus.

Such a switch can cause the LEDs in the device to flash.

Not only LED lamps, but also CFLs are susceptible to flashing. The device of their PRU (starting-regulating device) works on a similar principle, which allows the capacitor to store energy.

Consider an example of a simple LED lamp repair:

Can purchased LED bulbs be repaired? This question, taking into account the high cost of lamps, is quite relevant, a lot has already been written about this on Internet forums. Most often, the issues of repairing lamps bought on Aliexpress are discussed.

In the article "Shopping on Aliexpress - personal experience of shopping in a Chinese online store", among other things, it was told about the purchase of LED lamps, which are so popular recently. Actually, the article began with these lamps: the quality of these lamps left much to be desired, mainly attracted by the low price. But in some places where too much illumination is not required, these lamps came in handy.

With further use, it turned out that these lamps are not as durable as advertised. If the lamps of the Navigator trademark have been working trouble-free for the author of the article for almost two years, then the lamps bought at Aliexpress will fail in a month - another, or even earlier. An indicative case is when the lamp, replaced in the evening, simply did not turn on the next day. As a result, two faulty identical lamps.

Someone else would have just thrown away the unusable lamp, but not the radio amateur. Therefore, radio amateurs first try to find out the scale of the disaster, and, if possible, eliminate the defect. So it was this time.It's not that Chinese lamps are too expensive, but if they can be restored, then you won't have to buy another lamp. As they say, the savings are obvious.

The appearance of these lamps is shown in the figure.

This picture is taken from the Aliexpress website. Apparently, the sellers assumed that someone would disassemble and repair such lamps, moreover, repairs, as they say, are not far off. A larger board is shown in the figure below. From the inscription on the board, it is easy to understand that the lamp is assembled from 34 LEDs of standard size SMD2835 (2.8 * 3.5 mm).

Disassembling the lamp revealed that there is a small power supply board inside. In the photo, only capacitors are visible, all other parts are made by SMD installation and are located on the back side of the board.

The circuit assembled on the board is shown in the figure below. It’s impossible to come up with an easier one: a conventional transformerless power supply with a quenching capacitor.

The purpose of the parts is clear: resistors R1, R3 discharge capacitors after disconnecting from the network. This is done in order not to pinch the current when you touch these capacitors with your hands. With regard to capacitor C1, everything is clear. If you unscrew the lamp from the socket, the touching of the base may not be very pleasant. It all depends on what charge remains on the capacitor C1.

The charge on the electrolytic capacitor can remain only if at least one LED is cut off. This charge can be "felt" only by disassembling the lamp. Although the resistor R3 has one more purpose.

In the event of a burnout of the LED chain (at least one LED), the voltage across the electrolytic capacitor remains at a level not exceeding the operating voltage of the electrolytic capacitor.

In the diagram, the operating voltage of the electrolyte is 250V. If we assume that the voltage drop across one LED is 3V, then 34 * 3 = 102V will drop on 34 LEDs. It turns out something like a parametric voltage regulator. Therefore, in theory, 250V is more than enough.

Apparently, the Chinese developers reasoned in a similar way: there are lamps in which the operating voltage of an electrolytic capacitor is only 100V. Basically, these are small-sized lamps with a power of 3 ... 5W, where it is difficult to hide a high-voltage capacitor. In the lamp shown in the photo, the operating voltage of the electrolytic capacitor is 400V. But the resistor R3, most likely, will not be superfluous.

Resistor R2 is designed to limit the current through the LEDs. But this is only in the diagram. In fact, there is simply none on the printed circuit board inside the lamp. The function of limiting the current through the LED chain is successfully performed by the capacitor C1. This is a variant of the scheme. Maybe other manufacturers still install this resistor.

So, as it was written a little above, two faulty lamps turned out to be available at once, each only had one LED burned out. Moreover, there were no visible defects in the form of soot on the board, destruction or blackening of the LED itself. Therefore, the faulty LED had to be found. It is quite simple to do this: when dialing with a digital multimeter, the LEDs light up weakly. Naturally, if the probes of the multimeter are connected in the forward direction.

It was decided to use one lamp for spare parts, remove the LED from it and re-solder it to another. Attempts to unsolder the LED using a hot air gun were unsuccessful: the LED did not want to be unsoldered.

The fact is that on the reverse side of the printed circuit board there is an aluminum heatsink, because LEDs, like all semiconductor devices, do not like high temperatures very much. But even without a heatsink, the process of soldering parts from a printed circuit board is much more complicated and dramatic than soldering new parts onto a board.

Repair should be started by searching for a faulty LED if the lamp went out completely and immediately. If the lamp starts blinking, or just shines faintly, then the malfunction lies in the power supply. Most often this happens due to a malfunction of the capacitor C1.

The easiest repair option is to replace capacitor C1 with a known good one. A faulty electrolytic capacitor can almost always be identified by eye by a swollen bottom. This is how modern explosion-proof electrolytes behave.

After detecting a faulty LED, it is easiest to unsolder it as follows. The first thing to do is to remove the yellow elastic filter with a thin screwdriver or needle. There will be a metal surface with a crystal under it. Put a piece of solder and a small amount of gelatinous flux on this surface. With a well-heated soldering iron with a power of at least 60 ... 80W, warm up this "sandwich" until the LED is unsoldered from the board.

Somewhat better results can be achieved by using a low-melting alloy such as Wood's alloy instead of solder. Such an alloy in the form of small cakes is sold on radio markets. When mixed with a base solder, usually lead-free, Wood's alloy lowers the melting point of the lead-free solder. Therefore, the desoldering process becomes easier and faster, the likelihood of overheating the printed circuit board is significantly reduced.

Another way to unsolder a faulty LED is with hot tweezers. But not everyone has this tool, and it is hardly worth buying it for a one-time use. Therefore, it is better to make a U-shaped sting, or use the homemade sting shown in the figure below.

After the faulty LED is sealed off, it remains to replace it with a new one. LEDs of standard sizes 2835 or 5730 can be ordered in the same place where the lamps were purchased on Aliexpress. They are quite inexpensive there, about 50 rubles per hundred pieces.

Judging by the price, these are not the best LEDs, but the lamps were still repaired, and the glow of these LEDs is no worse than those that were originally.

Soldering a new LED to the board is not difficult. This can be done with a regular soldering iron. Remains of old lead-free solder should be removed from the board. This is best done with a wire braid with shielded wire.

The braid must be impregnated with flux, in the simplest case, with rosin. Then, with a well-heated soldering iron, pass through the braid along the contact pads, the solder is absorbed into the braid. Then irradiate the contacts of the board with POS 61 solder or the like.

Video (click to play).

Now it remains only to solder the LED installed on the contact pads. It is imperative to cover the LED contacts with a layer of flux, better than a gel-like one. After that, it is enough to touch the ends of the LED with a soldering iron to melt the solder remaining on the contacts of the board. Soldering is so fast that the finger holding the LED on the board does not feel any temperature rise.

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