Repairing the LED backlight of an LG TV matrix - step by step steps

Operating principle of LED/OLED matrices

It is important to know the operating principle of modern TV matrices for one reason - failure of the backlight is not such a serious problem.
The TV screen itself is made of millions of low-brightness color LEDs. In order to see the picture on the TV screen, the matrix is ​​equipped with a bright white LED backlight. It is its light, subsequently colored by the LED/OLED LEDs of the matrix, that we see on the TV. The design of the LED screen module of modern television receivers looks something like this: From the diagram it can be seen that the backlight is an auxiliary component of the TV screen module. The failure of this device does not in any way affect the operation of the screen itself. This is easy to verify. Turn on the TV (preferably with no light in the room) and direct the light from the flashlight onto the screen. In the place where the light from the flashlight falls, the picture currently displayed on the screen will be visible.

For 42″ LG TV models LB and LF series (2014-2015)

LG 42LB550V. LG 42LB551V. LG 42LB552V. LG 42LB5500 LG 42LB560V . LG 42LB561V. LG 42LB563V. LG 42LB565V LG 42LB5600 . LG 42LB569V. LG 42LB570V. LG 42LB572V LG 42LB5700 . LG 42LB580V. LG 42LB582V. LG 42LB588V LG 42LB620V . LG 42LB6200. LG 42LB628V. LG 42LB629V LG 42LB650V . LG 42LB652V. LG 42LB653V. LG 42LB658V

LG 42LF550V. LG 42LF551C. LG 42LF5500. LG 42LF560V. LG 42LF562V. LG 42LF564V. LG 42LF5600 LG 42LF570V . LG 42LF5700. LG 42LF580V. LG 42LF5800 LG 42LF620V . LG 42LF6200. LG 42LF6500. LG 42LF650V LG 42LF652V . LG 42LF653V.

collected on matrices:

LC420DUE-FGA3. LC420DUE-FGA4. LC420DUE-FGA5. LC420DUE-FGA6 LC420DUE-FGA7 . LC420DUE-FGP1. LC420DUE-FGP2. LC420DUE-MGA6 LC420DUE-MGA3 . LC420DUE-MGA4. LC420DUE-MGP2. LC420DUH-MGP1 LC420DUH-FGA1 . LC420DUH-FGP1. LC420DUH-FGP2. LC420DUH-FGA1

rulers with strip numbers are used:

4 strips A. 4 strips B 8 strips of 4 LEDs with lenses on the strip (6V diodes LATWT421RXLZK)

6916L-1956A – LG INNOTEK DRT 3.0 42″_A TYPE REV01 – 4pcs

6916L-1957A – LG INNOTEK DRT 3.0 42″_B TYPE REV01 – 4pcs

6916L-1709A LED1 (Innotek DRT 3.0 42”_A type Rev01) 4 pcs 6916L-1710A LED2 (Innotek DRT 3.0 42”_B type Rev01) 4 pcs

6916L-1756E LED1 (Innotek DRT 3.0 42”_A type Rev01) 4 pcs 6916L-1757E LED2 (Innotek DRT 3.0 42”_A type Rev01) 4 pcs

Reasons for the backlight not working

Failure of the backlight may be due to one of two reasons:

1. Problems with the backlight itself.
2. Malfunction of the backlight control module (driver).

Sometimes the backlight does not work due to both reasons at the same time, but this is a fairly rare occurrence.

The very malfunction of one or another electronic component of the TV screen most often becomes a consequence of voltage drops in the electrical network. If the power supply of the television receiver receives a voltage that does not correspond to the values ​​required for operation, it may malfunction. Bursts in output current, voltage, frequency, etc. may cause burnout of the backlight itself or the control module. Often the only way out of the situation is to replace burnt out components.

Can I replace the backlight myself?

The backlight is a fairly simple electronic component. It consists of several tens or hundreds of white LEDs. Typically, these LEDs are combined into strips arranged horizontally or vertically with the same distance between each other. For example, the photo below shows the backlight module for LG TVs of the 42LA6230 model range:

Each of the 5 LED strips has 10 LEDs in its design, i.e. there are 50 of them in total. The strips can be unsoldered from the backlight module and then just as easily replaced with new ones.

A special case of backlight failure—the burnout of one or more LEDs—is shown in the image below:

From here you can see that the LED strips are located behind the TV screen module. Those. they can be repaired or replaced at any time. But it is not recommended to do this without experience in repairing delicate electrical equipment.

We diagnose the TV

Diagnostics refers to identifying the reasons why the backlight on an LG TV has disappeared. If you try to start the TV panel from the remote control, but the image does not appear, then you need to shine a flashlight on the screen. A faded image should appear there. This flashlight served as a backlight. Based on this, we can conclude that the problem is a broken driver or burnt-out LEDs. In order to more accurately determine the problem, you will need to remove the back panel and conduct a visual inspection of the hardware.

The case can only be disassembled if the warranty period has already passed. Otherwise, your TV will not be eligible for free repair.

If you do not have any knowledge of electronics or repair of TV panels, then it is better to leave all the work to masters and qualified specialists. Otherwise, you risk aggravating the situation and completely breaking the device.

To replace the LEDs on LED TVs, you will need to disassemble the panel. To do this, unscrew the holding bolts on the TV cover. After this, use a voltmeter to gently measure the backlight voltage. If it is 100 volts or lower, then it is the one that has failed. Clear lighting is achieved due to LEDs in the LED backlight, which are located around the perimeter of the screen. To get to them, you will have to dismantle the matrix. To disassemble the device, follow the instructions below:

1. Disconnect the cables and unscrew the bolts to remove the T-con board.
2. Remove the protection from the decoders by unscrewing the fasteners on the sides. Proceed with caution, because the decoders will then only be secured with rubber fasteners.
3. Unscrew the bolts around the perimeter of the frame. Place the device on the back wall of the case and remove the frame.
4. Carefully turn the panel over so that the matrix does not fall off.
5. Carefully disconnect the rubber fasteners and remove the matrix.

Determining non-working LEDs

After you have put the matrix aside, you can begin to identify the burnt-out elements in the LED backlight. To replace you need:

1. Unclip all connections and remove the plastic frame.
2. Remove the scattering film.
3. The number of LEDs depends on the LG TV model.
4. A series connection is characterized by the fact that due to one diode the entire system may not function.

Typically there are about 18 diodes in the system. If the voltage measurement showed that 140 V is supplied, therefore, 7.8 V is supplied to each diode. Such calculations need to be carried out in order to calculate the power of the diodes used. To find a faulty diode, carefully inspect them for burning. This is the easiest way. But if no burns are detected, then you will have to check each diode separately.

We replace LEDs

Replacing LEDs in LED TVs is not easy, so if you are not confident in your knowledge, then it is better not to start. Another problem is that you will have to purchase a strip of light bulbs from the manufacturer, since service centers do not supply them. This affects the delivery time, so you will have to wait a while.

But you can also save money. You don’t need to buy the entire strip, but only a few LEDs to replace the burnt ones. They are purchased on the market. Usually they are sold already soldered, but it is important for us that they are working. The planks are fixed using double-sided tape. To disconnect the burnt-out diodes, you need to heat the tape with a hot hairdryer, after first fixing the bar on the prepared installation. The heated tin becomes soft, and you can remove faulty elements. Solder also using a hair dryer.

Lenses are attached at the factory using a compound, so be extremely careful when replacing them. In order not to disturb the focusing of the lenses, install everything in its place.

If you come across diodes with a negative area larger than the positive one, you will need to trim the contact point. If you damage the paint, don't worry, it's not that important. The lenses are glued using superglue.

Setting the current limit for LEDs

Manufacturers often overestimate the backlight level, setting it to almost maximum. This is done for advertising purposes to attract buyers with a bright picture. But over time, this can play a disservice and lead to LED burnout. Owners of LG TVs can independently reduce the current by increasing the value of the resistor - a special current sensor in a chain of series-connected diodes. The rule for calculating the resistor value is as follows: the resistor value will be equal to a value inversely proportional to the current in the diodes.

To reduce the current, you need to increase the resistance of the current sensor. They usually consist of paired low-resistance resistors. By removing one pair, we increase the sensor value and thereby increase the depth of the PWM NFE (Negative Feedback of the driver PWM controller) and reduce the current in the LEDs. If you remove two pairs of resistors, the current will almost halve, and this will significantly affect the brightness of the screen.

For TVs with dual 6-volt LEDs, there is a current reduction option. The current sensor consists of six resistors 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.

Selection of LEDs for LED backlighting of TVs by model table

In this article we will talk about LED backlighting of the TV matrix, or rather, what kind of LEDs are used in specific models; perhaps not a week goes by without our service desk receiving a letter or call with, to put it mildly, not the most competent question like “What kind of LEDs are on LG” or “how much do you have SAMSUNG LEDs?” , tolerance is tolerance, but such questions never cease to amaze. And having asked the client about the model, we get the answer - “I told SAMSUNG.” In general, jokes are jokes, and the idea to start keeping a log to further determine the model of the LED or backlight strips arose a long time ago.

All data for the table is taken exclusively from personal experience of repairs in our workshop; the “LED analogue” column indicates a proven replacement with successful operating experience.

Call or leave a request directly on the website! Our specialists will be happy to help you!

More possible problems and ways to solve them

Usually, expensive equipment is repaired at a service center, but sometimes the problem may turn out to be minor, and you can solve it yourself. Let's look at a few common problems and how to fix them yourself.

TV won't turn on

This problem is the most common, and almost every third LG TV owner encounters it. You shouldn’t immediately assume that TV receivers are of poor quality, everything is much more banal. The batteries on the remote control may be dead or the electrical cable may be damaged. Check that the plug fits tightly into the socket and that the socket itself is in good condition. If basic measures did not help or correct the situation, then you need to look deeper, namely in the hardware.

No image on screen

If the sound works, but the image is not displayed, then most likely the problem is the backlight. How to check the LED backlight on a TV is described above in this article. There may be several reasons:

• no current is supplied to the light bulbs if gas-discharge lamps are used;
• the diodes have burned out if strips with LEDs are used;
• scanning electrodes are faulty.

There is no image, but the bar is lit

The type of stripe can be different: located vertically and horizontally. This indicates that there is a problem with the sweep electrode. To confirm this, you need to connect another TV device with a working matrix. This situation can only be corrected by completely replacing the damaged part. If a spot appears on the display rather than a stripe, then the reason is most likely the same.

If backlight repair is required

Backlight repairs should be carried out in the following order:

1. Turn the TV device over and unscrew the fasteners on the back of the case.
2. Disconnect the cable from the chip boards.
3. Remove the latches on the matrix and unscrew the connecting elements.
4. Remove the top of the screen to access the diodes.
5. Use a tester to check the performance of each strip.
6. Identify the faulty strip.
7. Using hot air from a hair dryer, heat the tape under the strips and remove the faulty diodes.
8. Replace broken diodes.
9. Test the connection to the current and the flow of electricity.
10. If there are no problems, then tighten everything in the reverse order.

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One of the most popular problems faced by owners of smart TVs from the Korean company LG is when the TV completely loses the image, but there is sound. Symptoms associated with content transfer may vary:

• The device speaks but does not show.
• Unable to change channels due to black screen.
• The backlight does not work.
• The technique distorts the picture, turns it upside down, and it becomes necessary to change the display format.
• The TV is dim and dim.
• The broadcast on the display periodically disappears and the screen does not light up.

In this article we will look at what the causes of malfunctions may be, their elimination, and also what to do in each specific situation.

Matrix disassembly procedure

First, remove the decorative plastic panel

To do this, simply press the clamps around the perimeter. Note: this TV model is convenient because the matrix itself has an additional metal fastening casing, so you can safely press out the clamps with a knife without fear of damaging the glass.

After we have removed the decorative panel, we proceed to disassemble the metal casing. Again, this device is very convenient - the casing has screw fastenings around the entire perimeter, you just need to unscrew them

The casing consists of four plates; first the upper and lower ones are removed, and then the side ones

After the casing elements are removed, the matrix itself can be removed. Possible nuances: 1. During operation, dirt may accumulate around the perimeter of the matrix, and therefore the matrix can very easily stick. You should pay special attention to this - first you need to check whether the matrix can be easily removed by carefully prying its edges. It is highly not recommended to use metal objects for this; it is best to pry it with a fingernail, or, in extreme cases, with a plastic object such as a card). 2. The driver board cables are very thin and can be damaged very easily. You should definitely make sure that the driver board is free and does not touch the TV body when removing the matrix. You can secure it with a piece of electrical tape (as in the photo). 3. Take care in advance of where the removed matrix will lie while you carry out further repairs - it should be a flat and soft surface. For example, a table covered with a blanket.

After the matrix is ​​removed, you can begin to disassemble the plastic casing that secures the light-scattering films. To do this, you just need to press out the fastenings around the perimeter. In principle, nothing is fragile at this stage, so special care is not required here.

After we removed the light-diffusing films, we finally got to the LEDs themselves.

Replace matrix

The matrix cannot be repaired, and if faults are detected, it simply needs to be changed. Signs of a matrix malfunction are the LG TV freezing, slow response to commands, lack of response to launching applications, and the TV panel turning on and off instantly. It is better to replace the matrix at a service center.

Replacing the power supply

Most often, along with the backlight, the power supply stops working. You can determine that it is the one that has failed by the following signs:

1. The TV doesn't turn on.
2. The device does not respond to the remote control even after replacing the batteries and checking that the plug fits tightly into the socket.

The problem can be solved very easily and quickly by replacing the old unit with a new one.

Additional information on MainBoard repairs

The appearance of MainBoard EAX64891306 is shown in the figure below:

EAX64891306 can be used in TVs:

LG 32LN540V (Panel LC320DUE (SF)(R1)), LG 42LN542V-ZD (Panel LC420DUE SFR3), LG 32LN541V (Panel LC320DUE (SF)(R1)), LG 42LA615V (Panel LC420DUE (SF)(U2)), LG 32LA615V (Panel LC320DUE (SF)(U2)), LG 42LN540V (Panel LC420DUE (SF)(R1)), LG 42LN541V (Panel LC420DUE (SF)(R1)), LG 47LN540V (Panel LC470DUE (SF)(R1)) , LG 32LB530U ZA (Panel LC320DXE (SG)(R1)), LG 39LN540V (Panel HC390DUN-VCFP1-11XX), LG 32LA643V (Panel LC320EUN (SF)(F1)), LG 32LN542V (Panel LC320DUE SF R1), LG 47LA615 V (Panel LC470DUE (SF)(U2)), LG 47LA643V ZB (Panel LC470EUN (SF)(F2)), LG 32LN541U ZB (Panel HC320DXN-VHFP1 - 21XX / HC320DXN-VHFPA - 21XX), LG 32LN536U (Panel NC320DXN (SA )(P1)), LG 37LN541U (Panel LC370DXE (SF)(R1)).

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An indispensable author of our articles. In addition to knowing his business, he is a great person. Knows many unusual facts about technology and electronics. For many years he repaired all types of electronic devices.

• published articles - 54
• readers - 11 578
• on the website from December 15, 2021

Users encounter this kind of glitch quite often. Carry out diagnostics to determine why there is no picture on the LGI TV, but there is sound. Mostly the reason lies in the malfunction of the hardware modules. However, software failures cannot be ruled out under any circumstances.

Users can fix some defects on their own. More complex breakdowns that require complete disassembly of the TV are best left to the service center specialists.