Do-it-yourself smd LED lamp repair

Is it possible to repair purchased LED lamps? This question, taking into account the high cost of lamps, is quite relevant, a lot has already been written on Internet forums about this. Most often, the issues of repairing lamps purchased on Aliexpress are discussed.

In the article "Shopping on Aliexpress - a personal experience of shopping in a Chinese online store", among other things, it was told about the purchase of LED lamps that have been so popular lately. 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 light 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 flawlessly for the author of the article for almost two years, then the lamps bought on Aliexpress fail in a month - another, or even earlier. An indicative case is when a lamp replaced in the evening simply did not turn on the next day. As a result, two faulty identical lamps.

Someone else would have simply thrown away a worthless lamp, but not a 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 you can restore it, then you won't have to buy another lamp. As they say, there are savings.

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 just around the corner. 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 SMD2835 LEDs (2.8 * 3.5 mm).

Disassembling the lamp revealed that there was a small power supply board inside. Only capacitors are visible in the photo, all other parts are made by SMD mounting and are located on the back of the board.

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

The purpose of the parts is clear: the resistors R1, R3 discharge the capacitors after being disconnected from the network. This is done so that it does not tingle with current when touching these capacitors with your hands. With regard to the capacitor C1, everything is clear. If you unscrew the lamp from the cartridge, then touching the base may not be very pleasant. It all depends on how much charge remains on the capacitor C1.

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

If the LED string (at least one LED) burns out, 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 on one LED is 3V, then 34 * 3 = 102V will drop on 34 LEDs. It turns out something like a parametric voltage regulator. Therefore, 250V, theoretically, is more than enough.

Apparently, Chinese developers also 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 ... 5 W, 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 that's just in the diagram. In fact, it is simply not 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. It's like a schematic. Maybe other manufacturers still put this resistor.

So, as it was written a little higher, two faulty lamps turned out to be available at once, each of them burned out only one LED. 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 multimeter probes are connected in the forward direction.

It was decided to put one lamp into spare parts, remove the LED from it and solder it to another. Attempts to solder the LED with a hot air gun were unsuccessful: the LED did not want to be soldered.

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

Repairs should be started by searching for a faulty LED if the lamp goes out completely and immediately. If the lamp starts flashing, or just dimly shines, 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 remove the yellow elastic filter with a thin screwdriver or needle. Under it will be a metal surface with a crystal. Place a piece of solder and a small amount of gel-like flux on this surface. With a well-heated soldering iron with a power of at least 60 ... 80 W, heat this “sandwich” until the LED is soldered from the board.

Somewhat better results can be obtained by replacing the solder with a fusible alloy such as Wood's alloy. Such an alloy in the form of small cakes is sold on radio markets. By mixing 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 thermal tweezers. But not everyone has this tool, and it’s hardly worth buying it for a one-time use. Therefore, it is better to make a U-shaped sting, or use a homemade sting, shown in the figure below.

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

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

Soldering a new LED on the board is not difficult. This can be done with an ordinary soldering iron. Remove any old lead-free solder from the board.This is best done using 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 over the contact pads, the solder will be absorbed into the braid. Then irradiate the contacts of the board with solder POS 61 or similar.

Now it remains only to solder the LED installed on the pads. The LED contacts must be covered with a layer of flux, preferably gel-like. 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 increase in temperature.

With a variety of lighting fixtures on the shelves of the country, LEDs remain out of competition due to efficiency and durability. However, a quality product is not always purchased, because in the 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 master, and the details are inexpensive. Today we will figure out how to check the lighting device, in which cases the product is being repaired and how to do it.

LED lighting fixtures have firmly entered 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'll talk about him today. Consider the scheme of the 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 radio electronics.

The 220V LED lamp driver circuit consists of:

• diode bridge;
• resistance;
• resistors.

The diode bridge serves to rectify the current (turns it from AC to DC). On the graph, this looks like cutting off a half-wave of a sinusoid. Resistances limit the current, and capacitors store energy by increasing the frequency. Consider the principle of operation on the diagram 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 all the prescribed time and do not fade, although there are “diseases” to which they are also subject. 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 lamps cannot be done indefinitely. It is much easier to eliminate negative factors affecting durability and not to buy cheap products. Savings today will cost tomorrow. As economist Adam Smith said, "I'm not rich enough to buy cheap things."

Before you repair the 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 out the driver elements. You will also need a soldering station.

A soldering station is needed to repair LED chandeliers and 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 soldering iron tip with a dense spiral. The more you lengthen the sting, the lower its temperature. It is 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 master faces is how to disassemble an LED light bulb. To do this, you will need an awl, a solvent and a syringe with a needle. The diffuser of the LED lamp is glued to the body with a sealant that needs to be removed. Sweeping gently along the edge of the diffuser with an awl, we inject the solvent with a syringe. After 2÷3 minutes, twisting lightly, the diffuser is removed.

Checking the disassembled LED bulb. Do not do this - it is dangerous

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

After disassembling the lighting fixture, pay attention to the LED elements. Often burned is determined visually: it has tan marks or black dots. Then we change the faulty part and check the performance. We will tell you in detail about the replacement 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 unsolder 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 corresponding 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 according to technical parameters.

The LED can be called with a multimeter without soldering from the printed circuit board

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

If you have a soldering station or a hair dryer, this job is easy. 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 from the LED strip. But it is worth choosing the ones 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 right choice of LED-devices, you need to know not only the general LED characteristics. Useful information about modern models, electrical circuits of working devices. In this article, you will find answers to these and other practical questions.

If the driver consists of SMD components that are smaller, we will use a soldering iron with a copper wire on the tip. During a visual inspection, a burnt element was revealed - we solder it and select the appropriate one according to the marking. No visible damage - it's more difficult. We'll have to solder all the details and call individually. Having found a 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 printed circuit board 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 that 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 luminaires) or incorrect choice of the block protection degree.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 PSU will have to be replaced.

The power supply for the LEDs looks like this

Very important! All work on replacing the stabilizing power supply for LEDs is carried out with the voltage removed. Do not rely on the switch - it may be incorrectly connected. The voltage is turned off in the switchboard of the apartment. Remember that touching live parts with your hand is life threatening.

It is necessary to pay attention to the technical characteristics of the device - the power must exceed the parameters of the lamps that are powered by it. Having disconnected the failed unit, we connect a new one according to the diagram. It is located in the technical documentation of the device. This does not present any difficulties - all wires are color-coded, and the contacts are lettered.

Deciphering the degrees of protection IP for electrical appliances

The degree of protection of the device (IP) also plays a role. For the bathroom, the appliance must be marked at least IP45.

Related article:

In order for the lighting to be stable, and the installed products last as long as possible, you should choose the right 12 V 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 lamp is the indicator light on the switch key.

The capacitor located in the driver circuit accumulates voltage, and when the limit is reached, it produces a discharge. The backlight of the key passes a small amount of electricity, which does not affect incandescent or "halogen" bulbs, 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 again switches to accumulation. There are two ways to solve this problem:

1. We take out the key from the switch and turn off the backlight. The method is simple, but the indication that increases the value of the switch is now useless.
2. We disassemble the chandelier and on each cartridge we change the phase wire with zero places. The method is more complicated, but it retains the functionality of the switch. In the dark it can be seen 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 subject to flashing. The device of their PRU (ballast) works on a similar principle, which allows the capacitor to store energy.

Consider, for example, a simple repair of an LED lamp:

Before you start repairing 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 housing with a base and a light filter, a LED power board, an LED module.

Having carefully disassembled the case, the insides of the electronic circuit will open before you. For the most part, 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 reader's information, let's say that the operating voltage of one LED is 3.3 Volts, and the semiconductor crystal current 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 are LED light bulbs made?In series 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 go to deliberate deception, 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 dissipation will also become higher, with which you can fight for a short time. This trick sets them apart from competitors, due to the greater brightness with the same declared power. However, it leads to light emission drop or destruction over time and bitter disappointment to the user.

So, having an idea about the design of the electronic circuit of our LED lamp, which does not work, let's 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, the failure is a burned-out LED. To carry out repairs, you must first find a diode that is visually different from the rest, for example, by the presence of a pronounced black dot, as shown in the photo below, and then replace it with a new one.

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

The current limiting resistor may also burn out. Working capacitors rarely fail, damaging the rest of the elements of the LED device with their failure.

Since you are studying this page, we hope that you have a soldering iron and a basic understanding of electronics. Now about the troubleshooting technique. Diode testing is possible both with a multimeter and with a crown with a 1 kΩ limiting resistor. Alternately putting the wiring on the outputs of the LED, the serviceable one will shine. A multimeter in the test position will also cause the LED to glow, as long as the polarity is correct.

If no problems are identified with the light emitter, we check the limiting resistor with a tester, in most circuits its value is about 100-200 Ohms. We recommend watching a more complex repair on the video: