LCD backlight. Repair LED backlight matrix TV UE32F5000AK LCD backlight LED

LED backlighting in modern TVs with liquid crystal screens today has several technological solutions. In an effort to increase the color gamut to better display colors, TV display manufacturers have developed new backlighting methods that are different from conventional LEDs.

RGB LED

To obtain a wide spectrum of white light, they began to use a triad of LEDs consisting of blue, green and red colors in the backlight.

It was an alternative to WLED with a white LED and a smaller color gamut. The lighting system with three different LEDs is called RGB LED. The color gamut of RGB backlit screens was greater than with white LEDs only or with fluorescent lamp CCFL. But there were also disadvantages: price, size, weight, different aging time for LEDs of different colors, which eventually led to a mismatch in the color of the image. Therefore, they abandoned RGB LED backlighting in favor of WLED.

RGB LED

WLED

Given the disadvantages of RGB backlighting, TV manufacturers have settled on the use of "white" LEDs. They are located either on the sides of the case or in one array behind the LCD matrix. With the help of special diffusers, the light from the diodes is evenly distributed over the entire screen.

Although we call these LEDs "white", they actually emit blue light, which passes through a yellow filter and is converted to white. Therefore, the use of white LEDs in screens back in 2010 gave a bluish tint to the image.

Over time, manufacturers have improved the components, and WLED backlighting has become quite efficient, but as far as the light spectrum is concerned, some disproportions in the display of colors are noticeable.

Such a peak on blue is due to the blue LED. Using a filter, you can get white light. And this filtered light hits the red, blue, and green sub-pixels to form the entire gamut-limited spectrum. Passing through the filters, part of the spectrum is lost, and the flux intensity at the frequency corresponding to blue will be greater than at red and green. Screen calibration can get the right colors, but these reasons allow a WLED-backlit screen to display colors in sRGB space only.

If a WLED display is going to show colors close to blue in an image (shades of blue), then the advantage in the blue spectrum can put pressure on other colors to be mixed in to create the tint. Therefore, the display of shades close to blue may not be correct.

This problem was also when using a CCFL lamp, but there the problem was with green. It was on green that the peak of intensity was visible.

Increasing the color gamut

In order to expand the color gamut beyond sRGB and move to the next color standard, changes were made to the WLED backlight.

And after the changes, they began to use the name GB-R LED or GB-r LED. Now instead of white LED use combined blue and green LEDs coated with red phosphor.

This technology allows you to get peaks in the spectrum in red, green and blue.

This technology is currently used in LG on AH-IPS matrices and Samsung on PLS. The use of GB-r LED technology achieves 99% coverage of Adobe RGB.

Some manufacturers in their screens use a different way to increase the color gamut. They take a mix of a blue and red LED and use a green phosphor for the light filter. This technology is called RB-LED or RB-G LED.

Hi all. Today, Samsung UE32F5000AK is being repaired with a “no LED matrix backlight” malfunction. I very rarely repair such TVs, since I don’t have the equipment or amenities to repair such equipment. But nevertheless, this time I decided to try, and the owner of the TV was very insistent.

So, let's begin.

Preliminary diagnostics of the TV

When you turn on the TV, there is sound, but there is no picture. The TV responds to the remote control and buttons. If you look closely, you can see that there is an image on the matrix, but there is no LED backlight. From this we can conclude that the backlight control driver itself is faulty, or some line of LEDs has burned out.

TV disassembly

Having determined the possible malfunction, proceeded to disassemble. Putting the TV with a matrix on the table, the first thing I did was remove the stand, which is held on by three bolts. Then I unscrewed the remaining 10 bolts around the perimeter, after which I was able to remove the back cover.

When removing the back cover, you need to follow the cable from the joystick, which must be disconnected, after which the cover can be set aside.

The TV consists of three boards, namely the power supply, on the board of which the backlight driver is assembled, on the left is the main board, and on the bottom is the t-con matrix control board.

Fault definition

In LED TVs, all LEDs are connected in series. This means that if any of the LEDs breaks, the entire LED backlight will stop working. As I said earlier, the main reasons two backlight faults: LEDdriver or LEDs.

If the driver is faulty, then for the most part, no voltage is supplied to the LEDs. If the line of LEDs is faulty, then a voltage of about 200 volts will go to the power supply terminal, sometimes it can pulsate from 150 to 200. This indicates that the driver is trying to light up the backlight, but there is no load as LEDs, and the driver outputs maximum voltage. This is how I personally understand this process.

Having removed the power supply board, I determined that the power to the LEDs is supplied through the D9101C to the capacitor, after which I decided to measure the voltage on it. Having connected the multimeter, it turned out that the voltage on it walks in the range of 190-210v.

This means that the driver is idling, and the problem is in the LED line itself. For me, this was not very good news, since I am very reluctant to take on the disassembly of matrices due to inexperience and lack of conditions for repair.

Disassembly of LED LCD matrix

With the motto "do no harm", I began to disassemble the matrix. Having prepared the second table, on which I will adjust the matrix, the first thing I did was disconnect the cable from the LCD panel to the T-con board. Having examined in more detail the structure of the TV, I saw that the matrix itself rests on 2 frames, which are fastened with latches. From the beginning, I removed the first frame. To do this, I put the TV on the back wall, and gradually, starting from the top, began to snap off the latches. Special attention turned to the bottom of the matrix, so as not to damage the cables. The top frame came off very easily.

Further, holding the matrix, put the TV on the front, plumes down.

Carefully took out the matrix boards (decoders) from the grooves so that they began to hang freely.

Matrix decoders removed from latches

I will say right away that this is such a painstaking process that my nerves were at the limit. Having released the decoders from the latches, he took the TV by the second frame and carefully lifted it. The matrix remained on the table.

Removed matrix

Having removed the matrix on another table, he continued disassembly. From clicking the second frame, he removed the diffusing film, got to the LEDs.

Under the LEDs there is a white reflector, which is held on by 4 retaining clips.

After removing them, I was able to remove the reflector.

The structure of the LED TV backlight.

As you can see from the picture, the TV matrix consists of five lines of LEDs, nine LEDs each. If we take into account that each LED is powered by approximately 3 volts, then we have that one line of LEDs uses about 27 volts (3 * 9 = 27). In order to check which LED burned out, we first find in which line the LED broke. To do this, we alternately connect 27v power to a line of 9 LEDs, and which line did not light up in that one and break. Next, we connect 3v power to each LED in turn, and look for which LED is off.

In my case, it turned out to be very easy to identify a burned-out LED, since it got very hot, as a result of which the diffusing lens on it changed color and recovered a little.

The temperature was such that textolite with reverse side also burned out.

Opening the lens, soldered the LED. For this I used a blow dryer. I applied flux on top of the LED, heated the board from below until it soldered off. Thus, I decided to solder a new one.

Searching for a new LED is another task. After going through the radio market several times, I found similar LEDs in one of the stores, though already soldered. The man dropped them out of the TV, on which the matrix was broken.

I soldered the LED in the same way using soldering iron. Having tinned the tracks, I put the LED on it with the desired polarity, and slowly warmed the textolite from below until the LED was soldered. It was not soldered very beautifully, since the white paint peeled off, but it was reliable.

Having applied 27v power to the ruler, it lit up beautifully. Having glued the diverging lens, I folded the matrix in the reverse order. It should be noted that the repaired LED is slightly different in color, but this is not noticeable at all in the operating mode.

After completing the assembly, the TV started working.

After running for 8 hours, I gave the TV to the owner. It is worth noting that such a repair was the first time for me, and I am very pleased with its result. Perhaps I did some things wrong, please indicate them in your comments.

Other LEDs for LED TVs:

Television manufacturers regularly introduce users to new technologies that improve picture quality. Approaches to combining TV screens and LED elements have long been mastered by the largest companies. Recently, the source of a bright and soft glow is also moving to displays. mobile devices. Users of traditional lighting based on LEDs can also appreciate the advantages of such a solution, but, of course, the backlighting of LED screens in TVs looks the most attractive. Moreover, it is complemented by other high-tech inclusions used by the developers of this technique.

Backlight device

In the creation of modules for the implementation of illumination, LED-arrays are used, which can consist of white elements of the LED glow or multi-colored, such as RGB. The design of the board for equipping the matrix is ​​specially designed to be integrated into the device specific model carrier. As a rule, on the left side of the board there are contact connectors, one of which provides power to the LED backlight, while the others are designed to control its operating settings. Also, a special driver is used, the function of which is associated with the controller.

In finished form, it is a row of miniature lamps that are connected in groups of 3 pieces. Of course, manufacturers do not recommend interfering with the device of such tapes, but if desired, you can physically shorten or, on the contrary, make the device longer. Also, the standard backlight of the LED screen provides the ability to adjust the brightness, supports soft start and is supplied with voltage protection.

Backlight classification by installation type

There are two ways to integrate LED backlight - direct and edge. The first configuration assumes that the array will be located behind the liquid crystal panel. The second option allows you to create very thin screen panels and is called Edge-LED. In this case, the tapes are placed around the perimeter of the inner side of the display. In this case, the uniform distribution of LEDs is carried out using a separate panel, which is located behind the liquid crystal display - this type of LED screen backlighting is usually used in the development of mobile devices. Adherents of direct backlighting point to the quality result of the glow, which is achieved due to the greater number of LEDs, as well as local dimming to reduce color streaks.

Application of LED backlight

The average consumer can find this technology in Sony, LG and Samsung TV models, as well as in Kodak and Nokia products. Of course, LEDs have become more widespread, but it is in the models of these manufacturers that qualitative shifts are observed towards improving consumer qualities. this decision. One of the main tasks that the designers faced was to maintain the operability of the screen with optimal performance under direct sunlight conditions. Also recently improved in terms of increasing contrast. If we talk about advances in the direction of the screen design, then there are noticeable reductions in the thickness of the panels, as well as compatibility with a large diagonal. But unresolved issues remain. LEDs are not able to fully reveal their capabilities in the process of displaying information. However, this did not prevent LED technology from replacing CCFL lamps and successfully competing with the new generation of plasma screens.

Stereoscopic effects

Modules based on LEDs have many abilities to provide various effects. On this stage technology development, manufacturers are actively using two stereoscopic solutions. The first one provides for the angular deviation of radiation fluxes with the support of the diffraction effect. The user can perceive this effect while viewing with or without glasses, that is, in the holographic mode. The second effect provides for a shift in the light flux, which is emitted by the backlight of the LED screen in the direction of a given trajectory in the liquid crystal layers. You can use this technology in combination with 2D and 3D formats after appropriate conversion or recoding. However, with regard to the possibilities of combination with three-dimensional images, LED backlights are not going smoothly.

Compatible with 3D technology

It cannot be said that LED-backlit screens have serious problems with interaction with the 3D format, but for the optimal perception of such a “picture” by the viewer, special glasses are required. One of the most promising areas of this development are stereo glasses. For example, nVidia engineers released 3D shutter glasses with liquid crystal glasses a few years ago. To deflect light streams, the LED backlight of the LCD screen uses polarization filters. In this case, glasses are made without a special frame, in the form of a ribbon. The built-in lens consists of a wide array of translucent lenses that receive information from the control device.

Backlight Benefits

Compared to other backlighting options, LEDs significantly improve the consumer qualities of television screens. First of all, the immediate characteristics of the image are improved - this is expressed in an increase in contrast and color reproduction. Top quality color spectrum processing provides RGB-matrix. In addition, the backlight of the LED screen is characterized by low power consumption. Moreover, in some cases, a reduction in electricity consumption of up to 40% is achieved. It is also worth noting the possibility of producing ultra-thin screens, which at the same time have a small mass.

Flaws

Users of TVs with LED backlight present criticize them for harmful effects blue-violet radiation to the eyes. Also, bluishness is observed in the “picture” itself, which distorts the natural color reproduction. True, in latest versions On high-resolution TVs, the LED-backlit screen is practically free of such defects. But there are problems with brightness control, which involves pulse-width modulation. During these settings, you may notice flickering of the screen.

Conclusion

To date, the segment of TV models with LED technology is in its infancy. The consumer is still evaluating the possibilities and advantages that an innovative solution can provide. It should be noted that the operational disadvantages of LED backlighting do not confuse users as much as the high cost. Many experts consider this factor to be the main barrier to the wide popularization of the technology. However, the outlook for LEDs is still promising, as their cost will decline as demand increases. In parallel with this, other lighting qualities are being improved, which further increases the attractiveness of this proposal.

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 figure out his role?
I'm interested in this, because I also want to disable it. I will hang the monitor on swivel bracket and I want to power it from a standard TFX power supply from a mini case, in which it will be assembled new computer for parents (with not very new components, with DDR3L memory and intel processor 3rd generation :). Today I conducted an experiment, applied 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 believed that 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 over the bedside table and there is just 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, which 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 this is more wires, plus more hassle with turning it on / off, and the efficiency of the power supply will not be much lower (total energy consumption when powered from the computer's power supply will decrease ~ 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 did an experiment with "PMS" today. This pin is supplied with 2.794 volts and only when the monitor is on. If the monitor goes to sleep or is turned off using the button on the front panel, then "PMS" immediately drops to zero. And it also turned out that the first coil produces 5 volts 1.5 amperes, and the second one simultaneously produces 12 volts 1.2 amperes (to power the main board) and 12 volts 3 amperes (to power the inverter). That is, with any shutdown or sleep of the monitor, 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 goes both as power to the main board and at the same time they are needed to wake up the monitor from standby).
So most likely "PMS" still comes from the main board to the power supply and is needed to run a highly powerful coil, but still I want to know the opinion of an expert, since I only judge from practice and from 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 constantly supplied during sleep or when the monitor is turned off 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 while the monitor is running. I just want to make sure the 12 volts don't damage the main board while sleeping or turning off the monitor.

2) In addition to supply from system block, I want to implement a dimmable LED backlight using variable resistance to avoid PWM diodes at low brightness (flicker). I understand that the diodes will heat up more, efficiency will drop (energy consumption will slightly increase), but eye health is more important. I myself do not know how to correctly calculate what power variable resistor needs to be put in the circuit. According to the manufacturer, the energy consumption of the tape is 9.6 watts per meter. The tapes are cut with a distance of 5 cm, and my matrix needs two strips of 45 cm each, that is, a total of 90 cm. And according to the manufacturer (which I do not 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 margin of power, at least 2-3 amperes. I would also like to put an additional conventional resistance in the circuit, so that at maximum brightness (where the variable resistance supplies power to the direct line), not 12 volts, but 10.5 - 11 volts, no more go to the diodes. This is necessary so that the diodes do not overheat at maximum brightness, as well as increase their service life, since it is still a pleasure to completely disassemble the monitor and the matrix box once again.

If it’s not difficult, then write the number or model (I don’t know how correctly) of variable resistance (you need with a handle, like a volume acoustic 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 watts to take a "simple" resistance, which will additionally lower 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 take 12 volts to power the diode backlight, where power will be lost when the monitor is turned off with its off button and sleep mode. I myself can find 12 volts as a tester, which disappear when the monitor is turned off and asleep, but I'm afraid suddenly they 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 building the most compact computer with standard components (that is, a standard power supply, a standard motherboard, processor, OP memory, even the presence of a laptop DVD drive There is). He brought the missing "RESET" button, the missing indicators to his face, replaced the terrible blue indication of computer operation with a warm orange one, put the DVD drive switch (so that it would not make noise unnecessarily when the computer was turned on) and the amplifier with speakers, and also attached the amplifier itself to the face and volume control. It only remained to wait for the dust filters to arrive on the case and the power supply and a 6-pin connector to bring the speakers out of the case and indicate their operation. I plan to fasten the speakers to the bottom of the monitor case, and bring the indication of their work to the bottom of the case of the speakers themselves (both of them will have the lower plexiglass glowing during operation). I was already glad that there was a little hemorrhoids left before the assembly of this Frankenstein was completed, and then they call me and say that the monitor has stopped working. It was a huge ambush :(
That's why I want to do everything as reliably as possible, so that it works for a long time and does not cause more trouble for at least 10 years o_O.

P.S.
Sorry for the abundance of questions, I'm just afraid to burn the main monitor board out of ignorance. 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 doing it on VA for a long time, especially on PVA), and it’s almost impossible to buy the same used one in good condition (in Moscow and St. Petersburg they occasionally appear on sale). But if you buy it remotely, you will get any darkening or scratches of 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 sat down to zero (apparently for this reason I sold them so that they didn’t finally get screwed up) and as a bonus from above, I I got 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, the parents do not notice them at all).