How to check the backlighting in the led TV

How to disassemble the TV and repair the LED backlight

Low power consumption, high brightness, stability of parameters during power surges. all this is LED backlighting for TV. Unfortunately, the backlighting of the LED TV screen is built on not quite perfect circuitry, which increases the likelihood of failure. However, there is a plus: with some skill and with a small set of tools you can repair the backlight of the TV matrix with your hands.

Backlight failure can be due to one of two causes:

Sometimes the failure of backlighting is caused by both reasons at the same time, but it is a rather rare phenomenon.

The malfunction of one or another electronic component of the TV screen is most often the result of voltage fluctuations in the electrical system. If the power supply of the receiver receives voltage that is not the required values for operation, it may malfunction. Flashes of output current, voltage, frequency, etc.д. Can cause the backlight itself or the control module to burn out. Often the only way out of the situation is to replace the blown components.

What is LED backlight?

The abbreviation LED stands for Light Emitting Diode, which from English translates as a diode emitting light. If we talk in the context of the television equipment industry, this acronym stands for the type of liquid crystal matrix and backlighting by light-emitting diodes.

Once the new type of backlighting was introduced for LCD monitors, manufacturers began to replace the abbreviation LCD in the model name with the designation LED. Of course, LG televisions are no exception to this rule.

In fact, the motive for such a change was more for marketing purposes than real necessity. The fact that LED matrix backlighting is not a fundamentally new technology for manufacturing television screens. This is simply an updated way of lighting. However, the trend has harmoniously caught on, so the term Light Emitting Diode is actively used even today.

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

It’s no secret that LCD screens are composed of pixels with liquid crystals. The position of the crystal in the pixel determines whether the cell transmits light. This is actually how the luminescence of the screen.

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

As for the backlight itself, it affects the brightness, color rendering, coverage, dynamic contrast. But it is still worth evaluating the parameters in combination, given the type of matrix and backlight.

Thus, buying a TV with LED backlighting, the user gets:

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

There is no point in arguing that modern TV devices with backlighting, consisting of LEDs, provide the most vivid picture. Dynamic contrast. adjusting the brightness of the LEDs for different parts of the monitor. The image becomes more realistic.

Controlling the brightness of the LEDs directly when you watch TV, has a positive effect on the black level. When dark shades appear, the backlight level decreases, as a result, the screen gets darker.

Repair LED backlighting LG TV. Personal experience

I had a chance to change the backlight of LG32LN570V. The article describes a little bit of repair and will be supplemented if the repair by this method or LEDs from China in the future will give problems.

I won’t describe the diagnostics and repair. TV sets have this widespread defect, there is a lot of information on the internet, let’s focus on the details, which were not looked for on the fly, or a few suggestions on the implementation.

For disassembly and assembly I like this video

What is the order of disassembly and assembly can be seen.

Now what options were possible and how I did it:

Should I change one LED or all of them?? I had two that didn’t work at all. On one strip, one was dimmer at low current and the other was dimmer than the one next to it. There is no sense in looking for and replacing one at a time, then the rest will fail.

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If one LED fails, first try to replace it and lower the brightness.

Replace the whole strip or just the individual LEDs?

Naturally, it is easier to change the plate, you do not need the ability to solder smd components. There is no need to remove and install the lens. A straight hand is enough to carefully disassemble the TV, disconnect the connectors from the slats, rip the slats off the double sided tape and glue new ones on. Minus slats. they can not pick up (not the proper distance between the LEDs) or run into poor-quality diodes, misaligned lenses and as a consequence of shines. I’m going to find suitable bars just did not find and took the LEDs on which the positive references in runet and excellent reviews on ali. Naturally, the LEDs are much cheaper.

How to remove the lens? It is better to heat the bottom with a blow dryer and picking up for example a thin screwdriver, press up, the lens will come off softly, the feet remain intact, then it sits well in the old places. There will be a gap for cooling the diode and you may not have to center it. If you don’t have a hair dryer, people carefully cut off. If the adhesive layer is left on the strip before heating it must be removed, the temperature will bend it.

Each lens should be placed in its proper place? In my TV, no, the lenses are the same, but just in case, I spread and glued the lenses in the order of removal and how they were turned (one side of all the lenses were a little roughness, they were attached to it in the manufacture). I had this roughness everywhere looking up the strip. The top is by the marking beads. Remains of factory glue sometimes remain on the pad sometimes on the stem. In theory if you mix it up or turn it around, the glue might get on the glue and tilt the lens a bit. The factory glue is very small, maybe it’s an extra precaution.

How to Desolder LEDs? I heated it with a blow dryer on top and moved it with tweezers. If you don’t have a hair dryer, you can use two soldering irons. Or with one soldering iron. scrape the LED down to the base with small wire cutters and a knife (cutter), then solder the remaining parts. Then use a copper braid to collect the rest of the tin. The solder on my strip was refractory, if the soldering iron has no temperature control, you need a more powerful soldering iron for soldering. The tapes are on a thick copper base, they can be heated quite a bit. I soldered the new ones with ordinary solder.

How to Solder the LEDs? Zalivat pad and LED with a minimum amount of solder. Use soldering iron to warm up the track at the bottom, the solder will melt and the LED will shrink. Press down and trim with an eraser on the back of a pencil. Clean solder off the strip with alcohol. If you do not have a hair dryer, two soldering irons or a powerful one with a sting “hatchet” warm the bottom. One do not need to do, if you heat the sides alternately diode if at all will sit down before overheating can sit crooked and give the light on the screen. If you heat on one side, the metal anode and cathode from the bottom are not connected, the second contact will be heated through the LED itself and if it then will work not the fact that will work long.

How to Glue LED headlight lenses? Never use super glue, the lens may get cloudy from the vapors. I glued it to the B7000. It seems to work successfully but there are concerns that the temperature can soften and break off. The good thing about this glue is that in case of a second repair the lens is easy to remove, the glue is cheap. If it falls off, I will glue it with construction adhesive. sealant. If you are confident in the quality of diodes and repair 100% can be glued to the epoxy and other two-component adhesives.

How to glue the LED strips (strips)? For one strip I had a good removal of the native double sided tape. remained on the body. I covered it to keep it dust free for the time of repair. The rest of the tapes I glued on the construction glue sealant. Bought which is for outdoor use (resistant to UV radiation, high adhesion, a wide temperature range, etc.).д.)

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Reducing the LED strip current It is necessary to find a way to suit your TV. At my LG 32LN570V LED Strip Controller (LED Driver) MAP3202 resistors R826 and R827 are removed. Even if you put less brightness in the settings, when you turn on the TV a few seconds shines at full brightness. You can search for your TV here.

Tips for Disassembly and Reassembly Hold the die in the middle with the top and bottom edge when transferring. Ideally wearing gloves so as not to leave greasy prints and dust on the matrix and light-screening films. Light scattering films must be placed in the same order as they were. I actually took everything off all together, put it aside and covered it with a dust cover. The matrix should also be covered with a dust cover.

LEDs LATWT470RELZK for TV backlighting ordered here. Price is a bit high, but delivery is lightning fast, you can read the reviews. Plus these diodes are the size of the substrate shape like the original or really the original.

If there is any problem with the replaced diodes.

Here’s what’s inside the TV. Case, LEDs power supply and motherboard, speakers that’s the whole night of modern TV

Removed TV matrix. White. light scattering films

TV after repair of the LED backlight

As I said before, if you have any problems with the diodes on the link above or something else, I’ll write an addendum.

How to Test a Backlight

The easiest and most effective way is already mentioned above. If you can see the image on the screen by shining a flashlight on it, you don’t even need to look for other problems. The decoders, power supply system, signal loops, graphics processors and other key components are working properly. The problem is in the backlight or its control unit.

To check the backlighting, you need to remove practically everything from the TV. But all this can be done accurately and quickly. Checking the backlight has two steps.

  • Make sure that the diode structure is energized. This task is solved by the LED driver, a separate circuit in the TV power supply. If there is no voltage at its output, the backlight will not work.
  • If there is voltage at the driver, examination does not reveal places of local overheating, loose conductors and damage of current-carrying paths, proceed to check each of the crystals.

Although you will need special equipment for the work, it requires only minimal knowledge and skill to operate it. The list of instruments includes a multimeter, a soldering iron (air soldering station) and sharp feelers. But the scope of knowledge is somewhat more extensive. From the repairman will need the ability to check the parameters of the circuit sections. Knowledge of the basic values of voltage, with which the semiconductor crystals work, will not be superfluous. You will also need neatness, skill and confident skills of soldering with an air dryer. Therefore, if all of this is not available, to proceed with their own repair is not recommended. It is better to apply to the service for qualified assistance.

Fault location

When turning on the TV remote control there is a sound, but no image. If you look closely, you can notice it on the matrix, but even better to direct the beam of light from a flashlight to the display, it will be seen that the image has appeared. So, the TV does not work backlighting LCD TV. From this it follows that there can only be two reasons:

  • The backlight control driver is defective;
  • LED backlight itself is defective, which means that one or more of the strips with soldered LEDs is burned out.

How to repair LG LED TVs. Let’s take the 32LB582V as an example. LEDs LED TV connected in series. When one of them burns out, the circuit is broken, so the whole backlight stops working.

If the cause is a faulty driver, then the LEDs will not connect because there is no voltage to them. You have to take the TV apart to look at all its parts visually and to find the malfunction. To do this, first remove the back cover, disconnect the legs of the stand, and then unscrew all the screws on the perimeter. If after that it still can’t be removed, then you have to find the locking bolt and unscrew it.

After removing the cover check the voltage. The output voltage from the driver is 220 volts. This means that it is functional and it tries to light up the LED backlight.

Now we check the voltage of the LED backlight itself. If it is very small, for example, only up to 100 V, it indicates that the LCD backlight of the TV is faulty. There is a need to get to the LED strips, which, to ensure good lighting, are installed in the TV across the screen. To get to it, you will also have to remove the matrix.

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Connecting an external inverter to the monitor power supply board

Connecting the inverter to the monitor power supply consists of connecting all the necessary wires to the appropriate pins. Once their match is determined, it remains only to choose the best way to connect the wires. This can be done in different ways:

  • by wiring up the sockets on the connectors;
  • By soldering the contacts of the inverter to the power supply board;
  • by removing some of the insulation from the power supply wires leading to the controller board.
check, backlighting

All of these variants give the same connection scheme and differ only in the points of direct contact of the wires. The most reliable option is the second method, because soldering provides the strongest and most reliable contact. However, if a soldering iron is not available, any other connection method will do. Compulsory condition would be reliable insulation of joints, for which it is better to use heat shrink tubing.

What is a monitor backlight inverter

An inverter is a device that converts 12 VDC into an operating voltage for fluorescent tubes. The output is a high-voltage alternating current. To backlight the matrix on a monitor, multiple lamps are used, arranged either along the perimeter of the screen or fully occupying its entire area. The tasks of an inverter include:

  • Conversion of direct current into alternating voltage;
  • Adjust and stabilize the power supply current of light bulbs;
  • adjusting the brightness of the backlight;
  • matching the resistance of the lamp with the output resistance of the inverter;
  • Short circuit or overload protection.

Interesting! There are a lot of designs and varieties of inverters. Each manufacturer makes its own designs specifically to work with circuits and assemblies in their monitors. This variety creates some confusion and makes it difficult to repair or replace problematic components. you need to have the same inverter, which is not always possible.

How to Test a Power LED with a Tester?

Just switch your multimeter to diode-check mode, and check your LED by touching its pins with the tester stylus. A functioning LED will even light up a little bit and you will see the voltage drop across the P-N junction in volts on the multimeter display.

To determine the rated current of an LED, you will need a tester called a multimeter. This method is also used for ordinary diodes. The test is carried out as follows: Connect the probe of the multimeter with the plus lead to the anode and the minus lead to the cathode.

Diagnostics of light strips

Backlight strip tester

Checking LED light strips is carried out with the help of a LED strip tester, which allows you to check both the entire circuit and each element individually.

Tester strip light is a simple device specifically designed to test the LED tapes, it also reads the parallel voltages of LEDs.

The tester works from a 220V network, to test the electronics, the instrument is equipped with two wires with metal terminals phase (red) and zero (black).

If you need to determine the polarity of the LED, in this case the tester can easily do it, when testing the LED, the reading on the instrument display should be positive, otherwise (negative readings), the diode should be turned around.

Digital multimeter

Diagnose the strip can be and multimeter, to do this, you should set the switch on the device in the “probing” mode. By closing the metal styli on the contacts of the diode, it will light up, and when you change polarity, it will give a negative value.

The method works, but in this way checking the LED tapes backlighting is reduced to testing each diode separately, which is acceptable and allows you to identify the faulty element in the circuit. Naturally, by replacing it, you can restore the operation of the tape.

To summarize, it may be noted that for frequent work with the LEDs is better to buy a tape tester backlight, but you can also use a multimeter, which is a very useful device.

Buy devices, LEDs and other useful products can be in online stores, and it is better to do it through the site of the return of part of the spent money Backit.

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