Diodes for backlighting Samsung 32-inch TV. Repair of LED backlight of UE32F5000AK TV matrix. What is LED backlighting
Liquid crystal (LCD) matrices, also called LCD (Liquid Crystal Display), have long been used in TV screens from many companies, including Samsung. The matrix itself consists of many cells (the number of pixels multiplied by 3), which contain liquid crystals that can change their position in space under the influence of an applied voltage. By changing their position, the crystals transmit different amounts of light through their cells, and the brightness of the glow of each cell individually changes. This principle is used to form an image on the screen. To form a color image, each pixel is divided into three sub-pixels (RGB), therefore the number of cells was determined by the number of pixels multiplied by 3.
The crystals in the cells are controlled using thin film transistors (TFT), and based on the location of the crystals in the cells, several types of LCD screens are distinguished. The main types are TN, MVA and IPS. All these types differ in viewing angles, response time, contrast characteristics, color, etc. The buyer needs to know that IPS matrices are better than TN.
The LCD matrices themselves regulate only the light flux, but this light flux itself is created by the screen backlight. In the early years it was used for this Fluorescent Lamp(CCFL), and now you can still find quite a lot of TVs and monitors with a backlight. But since 2013, Samsung TVs have stopped producing models with a backlight.
To improve image characteristics such as brightness, contrast, color, all companies began producing screens from LED backlight– LED (Light Emitting Diode). With this type of backlighting, LEDs are placed around the perimeter of the screen (Edge method), or evenly behind the matrix (Direct method).
Experiments were carried out with different arrangements of LEDs, with different methods dimming, we used single-color and multi-color LEDs until we came to the same result. And at least in terms of image quality best results shows the Direct backlighting method, but in terms of quality-price ratio the Edge method is still mainly used. And Samsung LED TVs use only the Edge method, in which the LEDs are located around the perimeter of the screen. With this method of arranging LEDs, TVs have minimum thickness, which in some models is less than 1 centimeter.
Since 2013, as already mentioned, Samsung has stopped producing LCD TVs backlit by a CCFL lamp (Cold Cathode Fluorescent Lamp). Now in model range Samsung TV receivers have only LED TVs and models with a plasma panel as a screen.
Features of Samsung LED
Since the release of LCD screens, the main disadvantages of this technology have been attributed to insufficient contrast, especially compared to plasma screens. The use of ice illumination did not completely correct this shortcoming, but made it possible to combat it. Insufficient contrast of the LCD display occurs due to the fact that the liquid crystal cell, even in a completely closed position, transmits light and it is impossible to achieve a high-quality black level. So, using various technologies, the manufacturers decided to locally darken part of the screen, dimming the light of a group of LEDs in the area of the image where this moment many dark areas. Also in LCD displays with backlight from CCLF, by adjusting the brightness of the backlight, we achieved high levels of dynamic contrast, and in LED models this indicator has enormous values. But it is worth saying that dynamic contrast is not a characteristic of the matrix, unlike such a parameter as static contrast. You can read more about contrast.
Samsung uses Local Dimming and Micro Dimming technologies for high contrast ratios.
The use of LED backlighting in Samsung TVs makes it possible to reduce the thickness of the device, as well as its weight, and also reduce energy consumption. Screens with a liquid crystal matrix can be made from the smallest to 80-110 inches. So among the Samsung ice models you can choose a TV receiver of any size. High screen brightness with LED technology allow you to watch TV in any external lighting, whereas for plasma panels external lighting can be a problem. The service life of LEDs is not a problem today, and you will not have to change your TV soon because of this parameter.
LED TVs Samsung produces 6 series – from 4 to 9, which differ significantly in the range of functions and technical parameters. At the same time, the price also differs; the most expensive television receivers are the 9th series, and the simplest and cheapest are the 4th series. Each series still has several sub-series in which the technical difference is no longer very significant, but it still exists. All specifications and technical innovations change from year to year and are listed on the manufacturer’s official website or on specialized resources.
Hi all. Today we are repairing a Samsung UE32F5000AK with the fault “no matrix LED backlight”. I very rarely repair such TVs, since I have neither the equipment nor the amenities to repair such equipment. But nevertheless, this time I decided to try, and the owner of the TV really insisted.
So, let's begin.
Preliminary diagnostics of the TV
When you turn on the TV, there is sound, but 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.
Disassembling the TV
Having decided on possible malfunction, started disassembling. Having placed the TV matrix on the table, the first thing I did was remove the stand, which is held on by three bolts. Next, 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 keep an eye on the cable from the joystick, which needs to 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.
Troubleshooting
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 There are 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 illuminate the backlight, but there is no load as LEDs, and the driver displays maximum voltage. This process I personally understand it this way.
Having removed the power supply board, I determined that 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 was in the range of 190-210V.
This means that the driver is running idle, and the problem is in the LED line itself. This was not very good news for me, since I am very reluctant to take on the task of disassembling matrices due to my inexperience and lack of conditions for repairs.
Disassembling the LED LCD matrix
With the motto “do no harm,” I began disassembling the matrix. Having prepared the second table on which I will assemble the matrix, the first thing I did was disconnect the cable from the LCD panel to the T-con board. Having examined the structure of the TV in more detail, I saw that the matrix itself is supported by 2 frames, which are secured with latches. I removed the first frame from the beginning. To do this, I placed the TV on back wall, and gradually, starting from the top, began to unlatch 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.
Next, holding the matrix, I placed the TV on the front, with the cables down.
Carefully removed the matrix boards (decoders) from the grooves so that they began to hang freely.
Matrix decoders removed from latches
I’ll say right away that this is such a painstaking process that my nerves were on edge. Having released the decoders from the latches, he took the TV by the second frame and carefully lifted it. The matrix remained lying on the table.
Removed matrix
Having removed the matrix to another table, he continued disassembling. Clicking the second frame, I removed the scattering film and got to the LEDs.
Under the LEDs there is a white reflector, which is held on by 4 locking clips.
After removing them, I was able to remove the reflector.
The structure of LED TV backlighting.
As you can see from the picture, the TV matrix consists of five LED lines of 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 has burned out, we first find in which line the LED broke. To do this, we alternately connect 27V power to the line of 9 LEDs, and whichever line doesn’t light up is the one that breaks. Next, we connect 3V power to each LED one by one, and look for which LED is not lit.
In my case, it turned out to be very easy to identify a burnt-out LED, since it got very hot, as a result of which the diffusion lens on it changed color and got a little straighter.
The temperature was such that the textolite with reverse side also burned out.
Having pulled out the lens, the LED fell out. For this I used a soldering gun. I applied flux on top of the LED and heated the board from below until it was unsoldered. So I decided to solder the new one too.
Finding a new LED is another task. After going through the radio market several times, I found similar LEDs in one of the stores, albeit already soldered. The man unsoldered them from the TV, on which the matrix was broken.
I also soldered the LED using a soldering gun. Having tinned the tracks, I placed the LED on it with the required polarity, and slowly heated the PCB from below until the LED was soldered. It was not sealed very nicely, because White paint got off, but securely.
Having applied 27V power to the line, 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 in operating mode this is not noticeable at all.
Having completed 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.
One of the most common defects of LED TVs is missing screen backlight.
Visually, this defect looks very simple: “There is sound but no image,” but this is not entirely true. If you look closely at the TV screen and additionally shine a flashlight on it, you can see what action is happening on the screen. If this is the case, then the defect is most likely caused by a failed image diode backlight. As a rule, if one or two diodes burn out, the “brains” of the TV allow the backlight to continue to work, but a larger number is already critical and the backlight goes out completely. Some TVs still show an image when they start up, and then the screen goes blank, while some don’t show anything right away. This is caused by various software configuration, as well as the severity of the malfunction.
Today we will look at the example of the Samsung UE32F5020AK TV.
Any repair begins with disassembling the device and each device has its own nuances. In our case, you need to pay attention to the small cover, which must be removed before removing the main cover, because under it there is a connector into which the button control on the TV body is inserted and it must be disconnected. After that, unscrew and remove the main back cover.
The back cover is removed and we see all the insides of the TV. And that's all Motherboard(Main board), Power supply ( Power Supply Unit), speakers, cable to the T-Con board and T-Con itself (Time Controller).
We disconnect the loops coming from T-Con boards to the matrix strips.
Next, we begin to analyze the “Matrix”. It is recommended to be very careful when removing the main frame, since it is very well secured with latches. and many craftsmen prefer to use “spatulas” to pry up the frame and bend it, but there is one nuance in this issue and it must be approached very responsibly. The name of this nuance is “side matrix drivers”, popularly known as “Petals”. 
If you pry with a spatula or any other similar tool, you can hook the petal, or rather the crystal that is on it. As you can see in the photo, it is located just with inside drivers. Unfortunately, if the integrity of the crystal is broken, then a defect in the form of lines will appear on the image and it will be impossible to restore the integrity. Either you need to change the glass, or the matrix assembly, or the petal. But, unfortunately, it is almost impossible to carry out the last procedure in a stationary service center. And the price will not be much cheaper than replacing the matrix assembly (Unless, of course, we are talking about inexpensive TVs).
We removed the frame, did not catch anything and can continue further.
We make sure that nothing bothers us, there are no people nearby extra items(tools, devices), remove the matrix strips from the grooves, put on antistatic gloves and very carefully remove the glass. You can’t put it anywhere, since the glass is very fragile and you need to avoid interaction between the glass and anything as much as possible. We lean it against the wall behind the workplace. 
Then remove the frame on which the glass lay. It is secured in a circle with latches. It shouldn't be a problem to snap them off.
Removing polarizing sheets 
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And now we have almost reached the diode lines. The last sheet remains, but it is secured with clamps that play two roles. The first role is to hold the main reflector and the second role is to prevent the upper polarizing sheets from sagging.
On our TV, removing them will also not be difficult. They need to be turned and taken out. This is done by hand, however, if you can’t do it by hand, you can use a tool. The main thing is not to overdo it and not break them. .
So. Everything is ready for renovation. Now you need to identify the faulty diodes and replace them.
To identify faulty diodes, we use a special device.
A faulty diode may be either short-circuited or simply burnt out. These are two fundamentally different defects, since if a diode has burned out and is located, for example, at the very beginning of the line, then when the entire line rings, all the diodes except our culprit will light up. 
.
And if the diode is closed, then the line will not light up, since it will not receive feedback to ignite the remaining diodes. In this case, you will either have to ring each diode separately, or look for working segments. On this photo the second diode on the left is short-circuited, and the fourth one is simply burned out.
After searching for faulty diodes, we remove the rulers that have them and proceed to replacement.
We remove the diffusion lens from the faulty diode and check it again using the device.
We made sure that it really does not burn and proceed to replacing it. You can desolder and solder using either a soldering iron or a hair dryer. But in our opinion, soldering using a hair dryer is easier and better. For this work we use a soldering station.
We hang the bar in such a way that it is possible to use a hairdryer from below to heat the platform on which the diode is fixed and unsolder it. Next, we apply flux and attach a working diode to the pad and also solder it back using a hair dryer. It is important not to confuse the polarity of the diode, and it is also recommended to use the same diodes that are located on a specific bar, of course, not only in voltage, but also in shape. The site in our case looks like this
Very often, TVs with a similar defect come in for repair, but after another service, where, due to the lack of suitable diodes, they solder them anyhow. Of course, such work does not bring lasting results and has to be redone, and the Client has to pay additional money.
So. The diode has been replaced, we check it again with the device.
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The next step is to return the diverging lens to its place. This is a very serious step, because it determines how the diode will shine as part of an already assembled LCD module.
If the lens is not attached exactly in the center, but is shifted slightly to the side, then the dispersion will not be even, and, as a result, so-called halos around the lens will be visible on the scattering sheets instead of even light. And if the lens is shifted quite a bit, then most likely they will not be noticeable in the image or will be only on a bright white background, but if they are shifted very much, then they will be noticeable in almost any picture and any color.
Lenses have been replaced. We install the strips in their place, supply power to the TV and check. .
All diodes are on, the backlight has been restored. We begin to put our device back together. During the collection process, I recommend turning it on two more times. The first time we put all the polarization layers in place to make sure there were no ghosting. And also after we place (but do not secure) the glass.
Connected, checked, everything works.
Now comes the hard part! The last frame that covers the glass is the front frame of our TV. The point is that what more modern TV, the thinner the frames are used. There are different variations of frames. Some screw, others snap, but the main point one - the glass is placed on the frame in the grooves. The grooves are designed so that there are practically no gaps between them and the glass. Thus, if you place the glass a little crookedly and miss, and then snap the front frame, the result will be sad. If the matrix glass has even a small, unnoticeable chip, then, alas, the image will be ruined. Any slight damage to the matrix leads to irreversible consequences and it will no longer be possible to watch such TV.
So. The TV is assembled, the image appears. Everything is fine.
But our renovation is not finished yet. To ensure that this defect does not recur, we still need to improve the power supply. The fact is that a large current is supplied to the backlight to make the diodes glow brightly when required and, accordingly, the life of the diodes, which directly depends on the current, is reduced. We use the practice of reducing current to accordingly more life diodes. This does not affect the image quality, but it has a better effect on increasing the life of the diodes.
IN in this case We find a backlight resistor on the power supply. Its parameter is 3.4 ohm and change it to a larger one, or successively increase its parameter with another resistor. In our case, we took another 1.2 ohm resistor and soldered it in series to this one.
Now the current is reduced, the faulty diodes are replaced. The TV is assembled and handed over to the Owner.
With comparatively inexpensive work and the quick repair time, this TV will delight the Client for a long time, and we, in turn, received gratitude and positive feedback.
Attention! The information is intended for technically trained specialists!
Owners and users of TVs should remember that unqualified intervention can subsequently significantly increase the cost of repairing the TV or lead to its complete irreparability!
Many people have long known that in LED TVs of the fifth and sixth series of manufacturers Samsung and LG, which use matrices (LED panels) with direct backlighting of the Direct LED display, the LEDs can sometimes burn out already in the first or second year of operation.
Most popular models Samsung, which more often require backlight repair: UE32F5000..., UE32F5020..., UE32F5300..., UE320F5500... and others where panels are installed, for example, HF320BGSV1V, HF320BGA-B1 with direct backlighting.
Among LG TVs, models 32LN540..., 32LN541..., 32LN548 with LC320DUE and LC320DXE panels most often come in for repair with faulty LED backlighting.
Symptoms of a malfunction - there is sound, no picture. The LED driver is working properly and produces the maximum output voltage due to the lack of current in the load. An open circuit in the diode circuit can be checked with a current source (stabilizer).
When opening the panel, one broken LED is found and usually several more broken in the short circuit.
The fact is that protective zener diodes, mounted in the housing and connected parallel to the LED transitions in reverse polarity, are subject to avalanche and then thermal breakdown when the LED breaks. Usually the zener diode breaks into short circuit, and the current in the line is stabilized regardless of the number of remaining LEDs. The TV still works, the diffusers sometimes camouflage well from the owner dark spots on the screen.
This can happen with all the remaining LEDs until one of the zener diodes in avalanche mode breaks down not into a complete (S/C) but into a partial breakdown, for example, into a few ohms or tens of ohms. Then, heated up by the standard driver current, this remainder of the PN junction will simply burn into dust from excessive temperature exposure. As a result, we get a complete break in the LED and no current in the line, as well as a result that will force the user to contact a repair service - image disappeared.
Often, after 2 years of operation, we have to observe more than half of the broken LEDs.
Work on replacing LED strips (strings) or individual LEDs in strings has become commonplace for repairmen, but not all of the craftsmen realize to reduce the current of the LEDs and, in these cases, TV owners are soon forced to turn to them for help again.
Moreover, manufacturers (or their dealers) by default set the backlight level to the maximum position in all modes, most likely for advertising purposes, which significantly speeds up the failure of LEDs. And the user enjoys the quality of the contrast image and does not notice the catch. For the time being.
Manufacturers, for example, Samsung, send to their authorized service centers bulletins with recommendations for improving modules, which describe ways to limit the current in diodes by approximately 10%, which allows the TV to work at least guarantee period. On the modification of popular Samsung units BN44-00605..., BN44-00615..., BN44-00620..., if desired, the bulletin can be found on the Internet or downloaded.
There is almost always technical feasibility reduce the backlight current after replacing the LEDs.
Sometimes PWM controllers with an ISET (RISET) pin are used in driver circuitry to connect resistance R set and setting the maximum current value. Typically, resistors (two or more) are installed on the case from this terminal to allow the current to be changed within certain limits. By increasing the overall resistance R set, you can proportionally reduce the current in the LEDs.
In any case, the LED current from the LED driver can be somewhat reduced based on the driver circuitry, in particular the organization of Negative Current Feedback in the driver PWM controller. Usually in such cases it is enough to slightly increase the value of the resistor - the current sensor in the chain of series-connected LEDs.
The resistor value in ohms must be changed in inverse proportion to the current in the diodes.
Let's consider the operation of an LED driver implemented on the basis of a PWM controller, in our case in the picture SEM5027, which controls the width of the unlocking pulses in the gate of the transistor switch Q 1 .
The operation of such a Step-Up boost converter can be briefly described as follows:
During the open state of the key, the current from the output V
in through throttle L
, key Q
1 and resistor R
i goes to the ground and increases linearly, and the inductor core at this time stores magnetic energy. When the increasing current reaches a critical value for the transistor, the transistor will be closed by a comparator, which will operate according to the voltage on the measuring resistor R
i, increasing in proportion to the current in the inductor and the open switch.
After the key is closed, the magnetic energy stored in the throttle core will generate induced current in the winding, which will continue its path in the same direction, now through the diode D
, charging the capacitor C
.
The self-induction current charging the capacitor depends on the amount of stored magnetic energy, therefore on the time the key is open, that is, on the width of the pulses that unlock the key. In startup mode they are maximum and limited only by the voltage across the resistor R
i.
After just a few such trigger pulses, the voltage on the capacitor ( V
out) will exceed the input V
in and further, as soon as the LEDs open, a current appears in the load and a voltage proportional to it across the resistor R
d. This voltage is supplied to the control input of the PWM controller, internally inverted and supplied to the second input of the comparator, which will now close the transistor taking into account the OOS voltage on the resistor R
d. This will establish stabilization mode.
In other words - the time the key is open Q
1 within the period, which determines the voltage and current in the load, is stabilized by the negative feedback voltage (NFV) on the resistor R
d, proportional to the current in the LED line.
In essence, this current stabilizer is a flyback boost DC/DC voltage converter with load current stabilization.
Transistor Q
2 performs the function of an On/Off key - turns the backlight on and off and is not involved in stabilization, but the resistor value R
d, within certain limits allowed by the input parameters, will determine the current in the load in inverse proportion to the resistance of the resistor.
For example, in the popular Samsung power supply BN44-00605A with the above-described PWM SEM5027, the value of the resistor (current sensor) R9110 is usually increased from 3.6 Ohms to 4.3 - 4.7 Ohms, while reducing the current in the diodes by about 25%, which does not critically affect the brightness of the backlight, but allows us to hope that LEDs will soon will not fail again. 
There is a second way to reduce the backlight current in this unit, which is described in the bulletin; use the trimmer resistor VR9530 to set the voltage value of 1.044V on the resistor R9110. To do this, you must first add an 18 KOhm resistor in parallel with resistor R9509 to increase the adjustment range.
With edge lighting (Edge LED), the Samsung panel is an unsuccessful option LE320BGM-C1 installed in ultra-thin SAMSUNG TVs ES55 series, for example, in models UE32ES5500, UE32ES5507, UE32ES5530, UE32ES5537, UE32ES5550, UE32ES5557, which use LED strips like SLED 2012SVS32 7032NNB 44 2D with LEDs 7032
6V 120mA (180mA max) type TS732A.
Replacing such LEDs is more complex and requires appropriate practical skills from the technician. Moreover, the design and method of switching on LEDs in groups usually provoke a breakdown of the entire group of 11 series-connected LEDs. That is, at least 11, and more often 22 LEDs are detected in a state of breakdown.
Current limitation in the power supply BN44-00501A should be done by increasing the value of resistor R9131 (current sensor), which is installed from pin 8 (Sense) of the SLC2012M PWM controller to the case. In this version, the ON/Off switch of the driver is located inside the PWM.
Increasing the 3.5 ohm rating to 4.3 ohms will reduce the load current by about 20%.
To reduce backlight current on LG TVs eg popular LGP32-13PL1(EAX64905001), it is necessary to increase the resistance of the current sensor, which consists of a set of pairs of low-resistance resistors R822-R829, 4 pairs in total. Having unsoldered one pair, we increase the sensor rating by 25%, which increases the depth of PWM OOS and proportionally reduces the current in the LEDs. From 400 mA to 300 mA. 
If you remove two pairs of resistors, the current will decrease by half (to 200 mA), which affects the brightness of the screen.
LGP32-13PL1 power supplies are installed in LG TVs with Direct LED backlighting with three-volt LEDs on 2013 models, for example, 32LN5400, 32LN540V, 32LN541V, 32LN541B, 32LN541U, 32LN542V, 32LN548C, , 32LN575S, 32LA615V...
Panels used are LC320DUE (SF)(R1), LC320DUE (SF)(U2), LC320DXE (SF)(R1) ...
For each LED driver, with a technically competent analysis of the circuitry, another one can be found individual approach to limit current in LED strips.
IN difficult cases and in multi-channel drivers, it is practiced to reduce the current by changing the level at the controlled inputs of the PWM controller, but in this case, current limitation in abnormal modes is not guaranteed, for example, when the signal is turned on or in the absence of a signal, moreover, these inputs may already be used to control the backlight by the user from the menu.
Mass failure of the next generation of LEDs - dual (6 Volt 2W) are more common in LG panels, for example, NC320DXN VSBP1,LC320EUN (SE)(F3)... LC420DUE (FG)(P2) and others with similar LED strips. Twice the power is dissipated in the same housing as the previous 3 Volt 1W. Overheating in maximum mode is noticeable under the LEDs on the back of the strips. In order to increase the duration further exploitation, it is advisable to replace LEDs with signs of overheating prophylactically, since their PN junctions may already be partially damaged. The technology for replacing LEDs and limiting the LED driver current in these cases remains the same. To replace LG LED 3 Volt 1W panels, you can use Chinese analogues LATWT470RELZK (3528), and 6 Volt 2W can be replaced with dual LATWT391RZLZK (3535).
Let's consider one of the options, how to reduce backlight current on LG 32-inch TVs with power supplies LGP32-14PL1(EAX65391401) for six volt (dual) LEDs. 
The current sensor consists of six resistors R816-R821 connected in parallel - 1 Ohm, 1 Ohm, 1 Ohm, 1 Ohm, 2 Ohm, 8.2 Ohm. The total resistance in this case is calculated inversely proportional to their conductivity. This will be 0.22 Ohm. If you remove one 1 Ohm resistor, the total resistance increases to 0.28 Ohm, the current proportionally decreases from 250 mA to approximately 190 mA.
You can calculate the resistance of parallel connected resistors.
The LGP32-14PL1 power supply is installed in 2014 models 32LB551U, 32LB552U, 32LB5610, 32LB560U, 32LB561V, 32LB561U, 32LB563U, 32LB563V, 32LB565U, 32LB570U, 32LB572U 32 LB580V, 32LB628U, 32LB650V, 32LB652V, 32LF5800, 32LF580U...
Panels used are LC320DUE (FG)(A3), LC320DUH (FG)(P1), LC320DUH (FG)(P2), LC320DUE (VG)(M1), LC320DXE (FG)(A5), NC320DXN VSBP1, NC320DXN VSBP2, NC320DXN VSBP5 ...
TVs of the 32LBxxxx series (2014) are the most popular for repair. Currently, they are being delivered to workshops again, or in the third round, and need to replace the entire set of LEDs (18 pieces). Cracks on the radiating surface of the ice and dark spots (traces of overheating) on the bottom of the bar are eloquent confirmation of this.
Let's look at another popular power supply LGP32D-15CH1 for LG 32-inch TVs produced in 2015 with direct backlighting and dual (6V) LEDs. 
Improvement of the backlight is also achieved by increasing the resistance of the R816 2.4 Ohm current sensor to 3 or 3.3 Ohm. The backlight current will be proportionally reduced from the standard 250mA to 200 or 180 mA, respectively.
The LGP32D-15CH1 power supply is used in TVs 32LF560U, 32LF560V, 32LF562V, 32LF653V, 32LF564U, 32LF564V...
Panels used are LC320DUH (MG)(P1), LC320DXE (MG)(A3), NC320DUN-VBBP3, NC320DXH VSBP5...
Panels of large diagonals for TVs 42, 47, 50, 55 inches with 3V and 6V diodes are repaired using the same technologies. Their slats are made up of two halves, and the LEDs are the same as in 32-inch TVs.
In most cases, they have two channels, that is, two identical LED circuits connected in series and two current sensors.
We will briefly consider modifying power supplies to limit the LED driver current in them, and for two-channel options we will use one general picture below.
LGP42-13R2(EAX64905401), LED controller BD9483F with two channels in the load and two current sensors, used to power the LC420DUE(SF)(U1), LC420DUE (SF)(R4) panels in LG 2013 42LA620V, 42LA621V, 42LN613V. Backlight current sensors R811-R818 - channel 1 and R829-R836 - channel 2. All resistors are in pairs of 4.3 Ohm. To reduce the backlight current by 25%, remove one pair of resistors in each channel.
LGP3942-14PL1(EAX65423701) with PWM LED controller BD9486F used to power LC420DUE (FG)(P2) panels in 2014 LG TVs 42LB620V, 42LB629V. In this case, one channel. The backlight current sensor is a block of resistors R811-R818 in pairs of 4.3 Ohm. You can reduce the backlight current by 25% by removing one pair of resistors.
LGP3942D-15CH1(EAX66203001) with LED backlight controller LC5901, is used to power the LC420DUE (MG)(A3), LC420DUE (MG)(A6) panels in LG 2015 TVs 42LF550V, 42LF551C, 42LF560V, 42LF562V, 42LF564V, 42LF620V. The current in the LEDs is 250 mA. The current sensor is a resistor R816 with a nominal value of 3 Ohm. If you increase the rating to 4.3 Ohm, the current will decrease to 175 mA.
LGP4750-13PL2(EAX64905501) - power supply using an LED PWM controller BD9483F, used to power panels LC470DUE (SF)(R1), LC470DUE (SF)(R4), LC470DUE (SF)(U1), LC470DUE (SF)(U2), LC500DUE (SF) in 2013 LG TVs 47LN540V, 47LN570Y , 47LN613V, 47LA615V, 47LA620V, 47LA621V, 50LA620V. Current sensors in LEDs R811-R818 - channel 1 and R829-R836 - channel 2. Resistors in the channels in pairs of 4.3 + 3.9 Ohm. You can reduce the backlight current by 25% by removing one pair of resistors in each channel.
LGP55-13PL2(EAX64905601) - power supply with LED controller BD9483F for powering LA62M55T120V12 panels in LG 2013 55LA620V TVs. Current sensors in LEDs R811-R818 - channel 1 and R829-R836 - channel 2. Resistors in pairs of 4.7 Ohm, four pairs per channel. To reduce the backlight current by 25%, you need to remove one pair of resistors in each channel.
LGP55-14PL2(EAX65423801) - power supply with LED driver and LED backlight controller BL0202B for powering LC550DUH (FG)(P2) panels in 2014 LG TVs 55LB650V, 55LB652V. Current sensors in LEDs R811-R818 - channel 1 and R829-R836 - channel 2. Resistors in pairs, four pairs per channel. To reduce the backlight current by 25%, you need to turn off one pair of resistors in each channel.
Edge LED backlighting on LG TVs fails much less frequently. From cases in practice, we can recall the V236BJ1-LE2 REV.C1 panel with a strip LG Innotek 23.6 inch Rev0.1, used in TVs 24LB450U, 24LB457U, 24LF450U, 24MT45V and others.
The LED driver is located on the MainBoard board. To reduce backlight current, it is necessary to increase the total resistance of the resistors from pin 7 (RISET) to the housing for the controller DT1641AS. Strict proportional dependence will not be available due to availability additional control according to this input, therefore it is necessary to select denominations empirically.
Based on the experience gained in operating and repairing modern LED panels, the information will be updated.
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