The LED backlight of the LCD panel does not light up. Non-standard monitor backlight repair

Even the best quality equipment experiences various glitches and malfunctions. Therefore, every user should be prepared for the fact that they will have to repair the equipment with their own hands, because paying for the services of service centers can go broke.

Today we will talk about the most popular failure - a malfunction of the LED backlight on LG TVs. It is with this problem that ordinary users most often turn to service centers. Few people know that you can normalize the operation of the device on your own. No special skills are required, the main thing is to follow the instructions.

Before you start repairing the LG TV backlight, you should first understand how this component works, what are its functions and why is it even needed?

What is LED backlighting?

The abbreviation LED stands for Light Emitting Diode, which is translated from English as a diode that emits light. Speaking specifically in the context of the television equipment manufacturing industry, this abbreviation denotes the type of liquid crystal matrix and backlighting with light-emitting diodes.

After a new type of backlight for LCD monitors was introduced, manufacturers began to replace the abbreviation LCD in model names with the designation LED. Of course, LG TVs are no exception to this rule.

In fact, the motive for such changes was more likely to be marketing objectives than real necessity. The fact is that LED backlighting of matrices is not a fundamentally new technology for manufacturing screens for television equipment. It's just an updated way of lighting. However, the trend has harmoniously taken root, so the term Light Emitting Diode is still actively used today.

The most common TV matrices are based on the use of a cold cathode lamp, essentially the same as fluorescent lamps. As for LCD and LED models, they are characterized by light-emitting diodes.

It's no secret that LCD screens consist of liquid crystal pixels. The position of the crystal in a pixel determines whether the cell allows light to pass through. This is actually how the screen glows.

The quality of the screen matrix determines great amount parameters, in particular: the level of dark shades, viewing angle, static contrast, image refresh rate and even response time. Liquid crystal matrices are produced using several technologies. Let's list the most popular: TN, IPS, PLS.

As for the backlight itself, it affects brightness, color reproduction, coverage, and dynamic contrast. However, it is still worth evaluating the parameters as a whole, taking into account the type of matrix and backlight.

Thus, when buying a TV with LED backlighting, the user receives:

• balanced contrast;
• rich brightness;
• high picture clarity;
• color palette.

In addition, LEDs consume much less electricity, about 40%, than their counterparts. Fluorescent lamps, which are also used in the production of television equipment, contain mercury, which has a negative impact on the environment. In this regard, the advantages of LED are obvious.

There is no point in arguing; modern TV devices with backlighting consisting of LEDs ensure the transmission of the brightest image possible. Appears dynamic contrast– adjusting the brightness of the diodes for different areas of the monitor. The image becomes more realistic.

Regulating the glow of the diodes directly while watching TV also has a positive effect on the black level. When dark shades appear, the backlight level decreases, resulting in the screen becoming darker.

Reasons for backlight failure

High-quality television equipment can work for quite a long time, so problems with backlighting appear after an impressive period of time. Unfortunately, the same cannot be said about Chinese manufacturers.

Why is there no backlight? There are several reasons for the malfunction, let's analyze each of them:

1. A certain line of diodes has burned out. LEDs are characterized by a serial connection type, which means that if one element stops working, the entire component fails. However, voltage (approximately 200 volts) continues to flow to the light bulbs.

1. Problems with LED driver. The image disappears on the LG TV due to the fact that voltage, on the contrary, is not supplied to the LEDs, so they do not light up.

1. Manufacturing defects. Sometimes only one LED does not work, but the screen of the TV device does not light up.

1. The user sets the maximum brightness of the image, which leads to an increase in voltage, as a result of which the diodes cannot withstand and burn out.

1. Sometimes incorrect settings of the voltage supplied to the LEDs are the fault of the store where you purchased the TV. They try to attract customers with a bright picture.

Now you know why the LED backlight of your TV fails. This breakdown occurs quite often, but if you follow the manufacturer’s recommendations, you can significantly extend the service life of the device.

Professional repairmen using special equipment will determine which module has failed. How to the average user understand that the backlight of the LG TV screen does not work? Now let's look at the basics of diagnostics.

TV diagnostics

How to determine that it is the backlight that has failed? It all depends on the symptoms. For example, an LCD TV is started from the remote control remote control, but there is no image on the screen. Point a flashlight at the screen and you will see a dim picture. Essentially, the flashlight functions as forced illumination.

Based on this, we come to the conclusion that either the LED driver or the backlight is broken. To specify the source of the problem, you should disassemble the TV and carefully inspect the hardware components.

Remember that you should only disassemble the TV case if you have previously had similar experience. If you don’t have the skills, then it’s better to contact a service center. Once again it’s better not to take risks. Since there is always the possibility of making things worse, that is, aggravating the initial breakdown.

To dismantle back panel TV devices from LG, you just need to unscrew the special bolts that provide fixation. This is not difficult to do. First, disconnect the supply and remove the fasteners. If the cover still does not come off, then you need to find the blocking bolt.

With the back panel removed, you should check the backlight and output voltage. For example, if the backlight voltage is 100 volts, then the component has failed.

In most cases, LG TVs are equipped with an LED lens array, which is located around the entire perimeter of the screen, providing clear lighting. To get to this part and repair it, you must first dismantle the matrix.

Now you know what to do if the TV turns on, but there is no picture.

Disassembling the product

Regardless of the model, television equipment is equipped with three key boards: main, T-con and power adapter. You will see them immediately after removing the cover.

Disassembling an LG LCD TV is an extremely complex and time-consuming process; use extreme caution as there is a risk of damaging other hardware elements. To carefully disassemble the TV, follow these recommendations:

• prepare in advance the work area and two tables close to each other, on which the components will be placed: matrix, LED strip, bar;
• Before starting disassembly, wash your hands to avoid contaminating the filters or matrix. In the future, this will negatively affect the image quality;
• special attention should be paid to decryptors; if you are not careful, you will simply break the cable.

Step-by-step instructions for disassembling television equipment:

1. Disconnect the cables and unscrew the bolts located between them to disconnect and remove the T-con board.

1. Remove the metal protective elements from the decoders. To do this, unscrew the fastenings located on the sides and the bolts. As a result, decoders will be supported exclusively by rubber mounts.

1. It's time to remove the front frame of the device. Unscrew the screws around the entire perimeter and place the product on the back panel. Remove the frame.

1. Turn the screen over while holding the matrix. The decoders should be on top, you can disconnect the rubber fasteners holding them, the main thing is to do everything very carefully.

1. We disconnect the matrix and place it on a previously prepared table so that it does not interfere with the backlight repair.

In principle, anyone can disassemble a TV device, the main thing is to be as careful as possible.

Determination of non-working LEDs

Previously, we looked at the process of disassembling the TV, now let's proceed directly to the repair. To replace the LEDs in the backlight, carefully unclip all fasteners and then remove the plastic frame. We remove the scattering films to open access to faulty elements.

The structure of the LED backlight directly depends on which particular model of television equipment we are talking about. For example, for LG 32LB582V there are three rows of LEDs for 6 pieces. Model 32LN541U has one more diode in each row.

Television equipment that uses this lighting technology is characterized by a series connection of diodes, so if only one element burns out, then absolutely the entire system will fail.

If the driver breaks down, the entire system will lose power. If only one diode burns out, then there will be voltage, but there is no proper lighting. The circuit is open. Therefore, you need to change the faulty LEDs of your LG TV for correct viewing.

Approximately, the backlight system has about 18 diodes; voltage measurements showed that 140 V is supplied without loading, which means that each element separately accounts for approximately 7.8 V.

Why are all these calculations needed? The voltage level of each strip and the total load allow you to calculate the power of the LEDs used. Finding a faulty system element is extremely difficult. If the fasteners are not burnt, then you will have to recheck absolutely all the diodes one by one.

Replacing LEDs

Replacing the backlight of an LG TV yourself is extremely difficult, and it is possible that you will encounter certain difficulties. Let's assume that during the diagnostic process you were able to identify a couple of damaged diodes. Purchasing a strip of new light bulbs is very problematic. Service centers do not supply these parts, so the only option is to purchase from the manufacturer. It is clear that you will have to wait a very long time for delivery, not to mention the cost.

To avoid buying a strip, you should replace the LEDs in LED TVs LG alone. You can buy it on the market. Mostly they sell already soldered parts, but that’s okay, the main thing is that they work.

Remember that absolutely all planks are fixed with double-sided tape. Therefore, they need to be heated with a soldering hair dryer to loosen the fixation of the adhesive tape. Fix the LED strip in a special holder. Warm it up with a hairdryer from below, eventually the tin will melt. This is how the broken part is removed. Soldering is carried out in a similar way; this is the only way to change a part without damaging it.

Remember that in the factory, absolutely all lenses are attached with a compound, therefore, be extremely careful when dismantling them. Each of them will have to be installed in its place. So as not to disturb focus.

There is one more subtlety: it is possible that you will come across LEDs with a large negative platform, therefore, the positive one will be smaller. Trim the contact point to solder the diode.

If the paint is slightly damaged, that's okay. The remaining structural elements are soldered using a similar principle. As for the lenses, they need to be glued using superglue.

Note.

Hi all!

Sometimes, during renovation LCD backlight , difficulties arise in acquiring the necessary luminescent (CCFL ) lamps . In such cases, you can convert the lamp backlight to LED. Such a modification is not so difficult, and special problems does not occur with spare parts.

In this article I offer you the principle of such a reconstruction in the form of some instructions.

Replacement steps LCD backlight to LED:

Disassemble the monitor or TV. After removing the plastic case, carefully disconnect the wires from the board, remove the metal frame from the LCD module and remove the matrix. You need to be especially careful with the matrix so as not to damage the fragile connecting cables. If everything is done correctly, then full access to the electronic board, power inverter and backlight elements will be open.

2. Disconnect the pencil cases from lamps from the matrix or the lamps themselves, if they are installed without canisters.

3. Disconnect old lamps and recycle them. With elements CCFL You also need to be extremely careful, because they contain mercury.

4. We proceed to the replacement stage. First you need to purchase an LED strip, preferably with a reserve so that it is enough to replace all the lamps (measure the length of the lamp and multiply by their number). It should be as narrow as possible and have at least 120 LEDs per meter. To make the backlight more pleasing to the eye, it is better to take LEDs with a white glow.

5. The strip with LEDs must be glued with double-sided tape to where the lamps were. Next, wires from old lamps are soldered onto the contact terminals of the strips and insulated with hot-melt adhesive. You can immediately check the functionality of this design by connecting the wires to an external power source.

6. Now you need to connect the backlight to the power board of the monitor or TV. To do this, you need to find jumpers marked “12 V” and solder the backlight wires there, observing the polarity accordingly. Reassemble the monitor in reverse order and enjoy your invention.

Backlight in this case it will work when the device is connected to the network.

To control the backlight and bring it into normal mode, you will have to work hard. The wires leading to the LEDs must be powered in such a way that it is possible to turn on the backlight when you press the on/off buttons and adjust its brightness. There are 2 options for this:

1.We independently create a power supply circuit and adjust the backlight brightness:

• On the monitor or TV power chip we look for a plastic box (connector) with wires coming out of it, where each socket is labeled on the board.

• Here we are interested in the “DIM” output. It will be responsible for sending a signal to turn it on/off and adjust the brightness by changing the duty cycle in the PWM controller. The duty cycle of the pulses changes until the desired brightness level is established, and the limit values ​​will correspond to turning on and off.

• Now we need any N-channel field-effect transistor (field transistor). Wires from the LED strip with a minus are soldered to its drain (Drain), the common wire from the backlight is also connected to the source (source), and the gate (gate) is connected through a 100-200 Ohm resistor and any wire is connected to the “DIM” terminal.

• We still have wires from the backlight with a plus, we bring them to the +12V power supply on the microcircuit and solder them.

• Now we install the backlight in its rightful place and assemble the monitor in reverse order. Do not forget about caution and accuracy when handling the matrix and filters so that dust does not get in and the cables are not damaged. That's it, you can use it.

1. The second way, more expensive but convenient, is to buy a ready-made LED backlight with your own inverter :

• Again, pay attention to the plastic connector and DIM pin (brightness) and the on/of pin (it’s better to use the pinout).

• Using a multimeter, we determine the places on the control unit of old lamps from which the signal for brightness and on/of comes.

• Now solder the wires to the found places inverter new LED backlight .

• Also, it is better to unsolder the jumpers from the inverter power supply of the old lamps so that the backlight can be regulated by the new inverter.

• It's time to talk about the most common breakdowns of modern LCD TVs. Every day our service call center receives calls with the following content:

  • No image on screen
  • The screen went dark, but the sound remained
  • No picture
  • The image flickers
  • No visibility
  • The TV is blinking red
  • The image is missing

  Typically, LCD panels use two types of backlighting – lamp and LED:

  • Lamp lamps are small electroluminescent lamps, similar in design to those used in lighting industrial and office premises. The TV panels in which they are used are distinguished by a pleasant warm picture.
  • LED represents strips on which LEDs are soldered. They differ from lamps in lower energy consumption. The image when using this type of solution has a cooler and brighter picture.

  Above in the picture is the main component of the lamp backlight of the matrix, and below, respectively, is the LED backlight bar.

  Currently, lamp backlight technology is not installed in modern LCD matrices. This is due to the global trend towards energy saving and ecology. Lamps are characterized by high energy consumption and contain mercury. We will talk exclusively about the repair of LED lighting.

  There are two types of LED backlight:

  • Direct LED – A design feature of this solution is the arrangement of several horizontal or vertical rows of LED strips on the back side of the matrix. The advantages of this design are the uniformity of image illumination and the ability to selectively control the brightness of the backlight in different parts of the screen, which has a positive effect on the display quality. Lowering the brightness in the darker part of the image, or vice versa, increasing the brighter part makes the colors more contrasty. The main disadvantage of this engineering approach is the higher thickness of the TV.
  • EDGE LED – The placement of one or two strips on the sides or bottom of the panel allows you to design particularly thin TVs. The disadvantages of this technology are slight darkening in the corners of the screen
  
  

  At the top of the photo there is a Direct Led component, at the bottom there is an EDGE LED. Pay attention to how the lenses and diodes are located. In side lighting they shine from the side, and in rear lighting they shine from the top.

  
  

  This is what Direct Led backlight looks like inside a television panel.

  Let's talk a little about the main reasons for LED backlight burnout:

  • The main reason why LED diodes fail is that manufacturers force them to work at the peak of their parameters, which leads to accelerated burnout. We will not say that technology vendors do this on purpose, but some suspicions are hovering in our heads.
  • Another terrible enemy of diodes is power surges and thunderstorms. Often after such incidents, the backlight completely burns out. In spring and summer, during thunderstorms, the number of equipment with such defects coming in for repair increases significantly.
  • Factory defects are also quite common. Diodes already installed from the factory are defective, or overheated during factory soldering. Chinese brands are especially guilty of this. We don’t want to slander Chinese manufacturers, but often repairing such electronic equipment makes us sweat. This is due to the lack of such strict unification as that of Korean manufacturers.
  • One burnt-out LED can often also be the cause of a burnt-out backlight. Let's imagine that there are 18 LEDs with an operating voltage of 6 volts. Accordingly, for normal operation it is required that 18X6 = 72 (seventy-two volts) be supplied to the LED circuit. When one LED fails, the backlight, as a rule, does not close due to the zener diode present in the LED housing. It turns out that the remaining 17 LEDs receive 72 volts, which leads to accelerated burnout, when another LED diode dies, the same voltage comes to 16. And so on until everything burns out, or the current protection of the control driver trips and forcibly turns off the backlight.

  There are a huge number of types of LED strips. Often, the same model of TV and matrix can use several completely different types of brackets. This may depend on several factors:

  • Place of production, the same panel model can vary greatly depending on the place of TV production. Russian, European and Chinese assembly can vary greatly in the type of components used.
  • The same model can use dies from different manufacturers and, accordingly, different strips.
  • Production date – the manufacturer may change the design composition during the production cycle. A trivial reason for installing different spare parts may be the lack of the required spare part in the factory warehouse (they get out as best they can). In practice, sometimes it is necessary to greatly puzzle suppliers in order to find the necessary spare part. Well, we always try to have in our local warehouse the most extensive range of blocks necessary for repairs.
  
  

  Please note that all these brackets are installed in one Samsung TV model. The only difference is in the time and place of assembly (Europe, Russia and China). The strips differ significantly in the type of LEDs used, lenses, length and pitch.

  LEDs also never tire of delighting us with their diversity, differing in:

  • Current strength
  • Voltage
  • Cases
  • Location of the anode and cathode pads
  • Soldering parameters
  • Service life
  • Glow color temperature
  
  

  Notice how different the cases are.

  
  

  Contact pads also amaze with their diversity. In addition, in the same housing, the anode and cathode can be arranged in two options. Often, repairs by craftsmen who are not familiar with such nuances end in complete burnout of the backlight when soldering LEDs of the wrong polarity.

  As a rule, we use original LEDs made in South Korea. For Chinese TVs we use accordingly Chinese LEDs, except in cases of complete replacement. In such cases, we replace Chinese diodes with Korean ones due to the much higher reliability of the latter.

  Replacement of LEDs is carried out only if the required strips are missing due to the high complexity of the process. Resoldering a complete backlight consisting of 50 LEDs usually takes one working day; it is much easier to install new strips.

  Partial replacement of LEDs (replacing only burnt-out ones) is a rather useless exercise, since after a short time neighboring LEDs begin to die. As a result, everything ends with new repairs every 1 - 2 months.

  After backlight repairs, we limit the current by approximately 25 percent to increase service life. This is a recommendation from manufacturers that is sent in the form of bulletins to authorized service centers. Again, bad thoughts arise about manufacturers who at the factory set brighter operating modes for their factories, and if such equipment comes under warranty, they recommend forcing restrictions at the hardware level.

  For high-quality repairs, we use only original strips from the manufacturer.

  
  

  The photo above shows original spare parts for Samsung TVs. Having negative experience using non-original components, we prefer to use only genuine Repair Kits.

  Being responsible craftsmen, we are periodically surprised at how other service centers perform these types of repairs. Below we will provide photographs of such unsuccessful examples of service by incompetent technicians using components of dubious origin.

  
  

  Instead of completely replacing spare parts, cut out parts of used strips were soldered onto the top of the original ones. Due to poor heat dissipation, they burned out within 3 months. On top of that, the lenses were re-glued with Chinese “superglue”, as a result of which terrible spots appeared on the screen. The owner was unpleasantly surprised.

  
  

  This terrible work was carried out in one of the “houses of service”. Not finding the necessary spare parts, the master decided to cut the lighting from other strips. The strips were poorly glued to the body, resulting in repeated burnout without working for even three months. We made a complete replacement with a one-year warranty. Our customers brought us a full bucket of home-grown tomatoes as a token of gratitude.

  
  

  Another disgusting example of the clumsy work of the craftsmen. Due to the installed non-original spare parts, the backlight burned out and the screen began to glow a little. I had to completely change the backlight. We ask readers to pay attention to the cloudy lens, this is a consequence of the fact that it was glued with cyanoacrylate. As a result of the evaporation of the glue, the lens became cloudy; for such work it is necessary to use epoxy adhesives.

  
  

  Creativity of a rural radio mechanic. Diodes used for lighting the premises were installed. A careless technician also managed to damage the matrix, damaging the cable. Only with great effort did we manage to bring this TV back to life. The client recalled in a very rude manner the specialist who carried out the repairs before us.

  
  

  An example of the work of one well-known Minsk service. After the repair, the TV did not work for even two months. The owners took it under warranty where it stayed for 2 months. Tired of constant delays in repairs, the owners took the TV and handed it over to our service center. The next day the TV was ready, pleasantly surprising the customers. I had to completely change the backlight kit.

  
  

  Another work of unfortunate masters that did not last even two months. The insert was not properly bonded to the pallet, resulting in a very short service life. The client asked us to completely replace the lighting due to constant repairs in dubious workshops.

  
  

  Instead of changing all the LEDs or replacing the strips, the master decided to cut and assemble the strips, it worked for about a month. In an hour and a half, we replaced all the work of the previous specialist and gave the customer a long guarantee, after which he left satisfied.

  
  

  And this is how other craftsmen glue lenses. The result is terrible smudges on the screen. Judging by the color of the glue, certain unpleasant associations come to mind. In addition, this glue does not hold the lenses; by the time the TV arrived for repair, most of it had fallen off, worsening the already very bad picture.

  
  

  The guys also managed to install diodes used in lamps instead of the original LEDs for TV backlighting. The funny thing is that to make such a collective farm you need to spend quite a lot of time - purchasing LEDs and glue, making repairs and diagnostics. And as a result, you get low-quality work, wasting both your own and the customer’s time. Although it was necessary to simply install an original spare part from the manufacturer, which is not so difficult to find in specialized stores.

  
  

  But here the master couldn’t even glue the insert evenly, which was also from another TV. It worked for 2 weeks and broke down - when customers began to call the specialist with a request to carry out warranty repairs, he refused, citing the fact that he did not provide a guarantee for his work. By contacting us, the client received repairs within three hours and an honest one-year warranty on all lighting.

  
  

  But we saw such work - after disassembling the device, which had been in one notorious service, which periodically becomes the hero of an article on the website Onliner. This is a reflector sheet from Chinese TV. A peculiarity of Chinese engineering is that, unlike the Koreans, the sheets are not fastened with latches, but are glued with double-sided tape. Craftsmen with “hands off their shoulders”, instead of carefully cutting the sheet, began to pull it, completely tearing it. Not having anything similar, we decided to combine what was available, resulting in such a miracle.

  
  

  Let's summarize our article:

  • Z It makes sense to replace LEDs completely; replacing only burnt-out ones leads to a short service life of the product.
  • It is best to replace the backlight components immediately with strips.
  • Only original components should be installed. Savings have a negative impact on performance.
  • You need to be careful when choosing workshops that carry out repairs. A wrong choice can lead to financial and time costs.

  I also wanted to ask you about the “PMS” contact, which goes from the main board to the power supply or vice versa, from the power supply to the main board. Can't define his role?
  I'm interested in this because I also want to turn it off. I will hang the monitor on a swivel bracket and want to power it from a standard TFX power supply from the mini case in which it will be assembled new computer for parents (with not very new components, with DDR3L memory and a 3rd generation intel processor:). Today I conducted an experiment, supplied 5V, 12V and minus from the floppy drive connector from the computer power supply. The monitor worked fine and surprisingly even turned on and off with the power button (I assumed that the PMS sends a signal to the power supply to turn off the power to the inverter or the inverter and the main board at the same time). It’s just that the monitor will hang above the bedside table and there’s not enough space there, so it’s much easier for me to power it from the power supply, especially since I built a two-phase switch into the power supply that turns off zero and phase at the same time (that is, the computer is no longer needed unplug). And if you run a separate 220V cord to the monitor, then there are more wires, plus more hassle with turning it on/off, and the efficiency of the power supply will be slightly lower (the total energy consumption when powered from the computer power supply will decrease by ~5-10 watts). Power supply with "GOLD" certificate, Sea Sonic Electronics SSP-300TGS Active PFC 300W. Therefore, I need to know what the “PMS” signal does, wouldn’t its absence on the monitor’s power supply be critical?

  I also conducted an experiment with "PMS" today. 2.794 volts are supplied to this contact and only when the monitor is running. If the monitor goes to sleep or is turned off via the button on the front panel, then “PMS” immediately drops to zero. It also turned out that the first coil produces 5 volts 1.5 amperes, and the second produces simultaneously 12 volts 1.2 amperes (to power the main board) and 12 volts 3 amperes (to power the inverter). That is, whenever the monitor is turned off or asleep, 12 volts disappear from both lines, and 5 volts are supplied all the time while the monitor is plugged in and the main switch supplies 220 volts to the power supply (apparently 5 volts also goes as power to the main board and at the same time they are needed to wake up the monitor from standby mode).
  So most likely “PMS” still comes from the main board to the power supply and is needed to launch a high-power coil, but I still want to know the opinion of an expert, since I judge only from practice and logical guesses.

  And if possible, I have three more requests for you.
  1) You cannot look at the 12 volt circuit that comes from the power supply to the main board; it’s okay that 12 volts will be supplied constantly during sleep or turning off the monitor through the button on the main panel. As I wrote above, 5 volts work constantly from the built-in power supply, but 12 volts are supplied only when the monitor is running. Just want to be sure that 12 volts will not damage the main board while sleeping or turning off the monitor.

  2) In addition to power supply from system unit, I want to implement LED backlighting with adjustable brightness using a variable resistance to avoid PWM diodes at low brightness (flicker). I understand that the diodes will heat up more, the efficiency will drop (energy consumption will increase slightly), but eye health is more important. I myself don’t know how to correctly calculate what power variable resistor should be placed in the circuit. According to the manufacturer, the energy consumption of the tape is 9.6 watts per meter. The tapes are cut at a distance of 5 cm, and my matrix needs two strips of 45 cm, that is, a total of 90 cm. And according to the manufacturer (which I don’t really trust), the consumption at 12 volts is 800 milliamps per meter of tape, minus 10% = 720 milliamps. But it is better to take a resistance with a good power reserve, at least 2-3 amperes. I would also like to add an additional ordinary resistance to the circuit, so that at maximum brightness (where the variable resistance supplies power directly), not 12 volts go to the diodes, but 10.5 - 11 volts, no more. This is necessary so that the diodes do not overheat at maximum brightness, and also to increase their service life, since completely disassembling the monitor and matrix box once again is a pleasure.

  If it’s not difficult, then write the number or model (I don’t know how to correctly) of the variable resistance (it needs to have a knob, like the volume of speaker systems, since there is a good place in the back of the monitor where it can be brought out) and how many ohms (even more likely kOhm) and Watt take a “simple” resistance, which will further reduce the voltage from 12 volts to 10-11 volts.

  3) You also need to find a place in the power circuit of the main board, from where you can get 12 volts to power the LED backlight, where the power will be lost when you turn off the monitor from its power button and sleep mode. I myself can use a tester to find 12 volts, which disappear when the monitor is turned off and asleep, but I’m afraid that they suddenly pass through some kind of resistor or transistor, which can burn out from an additional load of 0.7-.08 amperes.

  For several weeks now I have been assembling the most compact computer with standard components (that is, standard block power, standard motherboard, processor, OP memory, even the presence of a laptop DVD drive There is). I brought out the missing "RESET" button and the missing indicators, replaced the terrible blue computer operation indicator with a warm orange one, installed a switch for the DVD drive (so that it would not make unnecessary noise when turning on the computer) and the amplifier and speakers, and also attached the amplifier itself to the face and volume control. All that remained was to wait for the arrival of dust filters on the case and power supply and a 6-pin connector to remove the speakers from the case and indicate their operation. I plan to screw the speakers to the bottom of the monitor case, and display the indication of their operation on the bottom of the case of the speakers themselves (the lower plexiglass of both will glow during operation). I was already glad that there was a little hemorrhoids left before the assembly of this Frankenstein was completed, and then they called me and said that the monitor had stopped working. It was a strong ambush :(
  That’s why I want to do everything as reliably as possible, so that it works for a long time and doesn’t cause any more trouble for at least 10 years o_O.

  P.S.
  Sorry for the abundance of questions, I’m just afraid of unknowingly burning the main board of the monitor. Considering that this model has not been produced for more than 10 years (and as I already wrote, there are no alternatives to it, of the modern ones there are only two models on IPS matrices; they have been making them on VA for a long time, especially on PVA), but to buy the same used In good condition it is practically impossible (in Moscow and St. Petersburg they occasionally appear on sale). But if you buy it remotely, you will get darkening or scratches on the matrix, as well as broken or burnt-out pixels. When I bought the second 2190UXp through Avito, the seller from St. Petersburg assured me that the matrix was ideal, and when the monitor arrived, it turned out that the lamps had gone to zero (apparently that’s why I sold it, so that they wouldn’t completely fail) and as a bonus on top, I I received two dead pixels (fortunately, at least the pixels are not in the center of the screen and on the VA matrix they are not so noticeable, parents do not notice them at all).

  In this article I will tell you how to replace the backlight lamp of a TFT LCD monitor with your own hands.

  A monitor came in for repairs with a “no backlight” fault. After switching on, the backlight flashed briefly on the monitor screen and then disappeared. The image was viewed normally. During the diagnostics, the power supply and inverter were carefully examined and tested. No deviations were found: visually all elements are intact, including capacitors =)) The measured supply voltages were normal. Then suspicion fell on the backlight lamps, which was ultimately justified.

  The test was carried out by connecting known-good backlight lamps instead of the standard ones, which are installed directly in the TFT matrix housing. When the monitor was turned on, the lamps lit up and the backlight worked for a long time without any complaints. Further, by exclusion, it was established that the lower backlight lamp was “guilty”. We will change it.

  ATTENTION! When disassembling the matrix, extreme care and caution should be observed, otherwise the matrix will be irreparably damaged and further repairs will be pointless!!!

  Disassembling the matrix should be done on a flat, spacious table surface, previously removed from screws and other objects, preventing them from accidentally falling under the matrix screen, since the latter may be damaged or scratched.

  Matrix assembly with removed metal frame:

  

  The matrix is ​​carefully removed. The remaining part is a light guide with backlight lamps in the housing:

  

  The plastic frame has been removed. Access to backlights is open:

  

  The lamps with their housing are placed on the main transparent light guide from above and below, respectively.

  Bottom light bulb removed:

  

  Burnt black cathodes are clearly visible in the photo:

  

  

  To replace the lamps, we first need to remove them from the metal housing. To do this, you need to carefully peel off the wires running from below along the metal body, and then VERY CAREFULLY pull out the dielectric lamp holders ( white, made of a soft material resembling soft rubber or hardened silicone) through which wires are threaded. After that, even more carefully, we try to pull them off the ends of the lamps without breaking the lamps. If everything went well, then cut the heat-shrinkable tube at the ends of the lamps and solder the wires. After this, we solder the new lamps and reassemble in the reverse order, being extremely careful. However, I would like to note that this method is very labor-intensive and the likelihood of damaging the lamps is very high (a slight bend and the lamp will crack).

  As practice has shown, the entire procedure for replacing backlight lamps can be simplified, while reducing the risk of damage to the lamps. To do this, we will not completely disassemble the lamp, but will do it as shown in the photo below:

  

  

  Using a sharp scalpel, cut out an area in the lamp holder that allows you to cut off the heat shrink from the ends of the lamps and unsolder the wire. This operation should be carried out quite carefully so as not to damage the wire insulation, and also not to get carried away with cutting the soft lamp holder, since it will lose its shape and restoring it will be very problematic, if not impossible.

  We do the same on the opposite side:

  

  This is what the bare end of a lamp with a soldered wire looks like:

  

  The wire is sealed off:

  

  And one end of the lamp is released:

  

  

  We cut off the old heat shrink and unsolder the second end of the lamp. It often happens that during dismantling, an old lamp cracks near the burnt-out cathode, exactly at the point of greatest heating. Just like in the photo :)

  

  

  

  We solder the wire, not forgetting to BEFORE putting on a heat-shrinkable tube of the appropriate diameter and shrinking it:

  

  Carefully insert the lamp into place and solder the second end of the lamp and insulate it using heat shrink. After this, we check again that the lamp is exactly in its place and fill the cutouts with hot glue or other suitable insulating sealant.

  If necessary, we carry out a similar procedure with the remaining lamps that require replacement.

  Once the lamps are assembled, you can check their functionality. In this case, you should pay attention to the absence of high-voltage breakdown on the metal body of the lamp. If this defect is detected, the procedure for insulating the ends of the lamp should be repeated or the violations of the wire insulation should be eliminated.

  The lamps glow without defects or complaints:

  

  Everything is fine, you can install the lamps in their place and completely assemble the display.

  In the assembled display, the lamps work no worse :), as can be judged by the glow of the screen through the slots of the metal frame:

  

  

  And this is what our repaired monitor looks like in operation:

  

  Good luck with your repairs!!!