LCD backlight
LCD backlight- a set of components that illuminate the matrix in LCD displays. Used to improve low-light readability in small displays, as well as computer monitors and LCD TVs.
The LCD displays of many portable devices are not backlit, so they require illumination from external light sources. However, most modern displays contain built-in backlighting.
The backlight itself consists of the following components:
- directly the light source (for example, a fluorescent lamp);
- a diffuser that provides uniform illumination of the entire display;
- inverter, which converts voltages and also controls brightness;
Types of light sources
- Miniature incandescent lamps;
- Cold cathode fluorescent lamp (CCFL);
- Hot cathode fluorescent lamp (HCFL);
- External electrode fluorescent lamp (EEFL);
- Single LEDs;
- LED matrix;
Monochrome displays usually have yellow, green, blue or white flowers, colored ones usually have white backlights.
Application
Small, cheap LCD panels typically use color LED backlighting, although recently white LED backlighting has become increasingly common. Large-area displays often use backlighting on electroluminescent panels, either colored or white. Most computer displays use cold cathode fluorescent lamps (CCFLs).
LED backlight
LED backlights for LCD displays are divided into categories according to the following criteria:
- glow color: white or RGB;
- lighting uniformity: static or dynamic;
- design: matrix or side.
RGB backlighting is used, as a rule, to fine-tune the light spectrum. In addition, additional compensation for changes in the emission spectrum of LEDs over time is often applied.
If the brightness of the matrix backlight is adjusted equally over the entire area, the backlight is called static. If it is possible to control the illumination of individual parts of the matrix (usually depending on the scene), the illumination is called dynamic.
Depending on the design, the LED backlight can be side-mounted, that is, installed on the sides of the panel instead of conventional backlights, thus requiring a diffuser, or behind the LCD matrix. In the latter case, the LEDs are organized into a matrix of one resolution or another, possibly with individual control.
Screen flickering
If the backlight brightness is controlled by pulse width modulation, the screen flickers subtly. This can be checked by shaking a pen or pencil against the background of the screen. If the frequency is too low, the silhouette of the handle will split into several (stroboscopic effect). People who are sensitive to flicker experience tired eyes and may experience migraines.
Links
Notes
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See what “LCD display backlighting” is in other dictionaries:
backlight (display)- backlight The light source of the LCD display operating in transmission mode. Modern LCD displays use two backlight technologies. Most TFT LCD panels use cold cathode fluorescent lamps and a diffusion panel... ... Technical Translator's Guide
Watch with LCD display ... Wikipedia
A transflective liquid crystal display (monitor) is a liquid crystal display that both reflects light and emits it (glows on its own). The term is derived from English words“pass” and “reflect” (transflective ... Wikipedia
In this article we will look at how you can repair a monitor yourself.
A modern LCD monitor consists of only two boards: a scaler and a power supply
Scaler- This is the monitor control board. His brain. Here the monitor converts the digital signal into colors on the display and also contains various settings. It contains a processor, flash memory where the monitor firmware is written, and EEPROM memory in which the current settings are saved.
Power unit. It supplies power to the monitor circuits. It may also contain an inverter for monitors with LCD backlight. LED-backlit monitors do not have an inverter.
The power supply for the monitor looks something like this:
There is also a significant difference. In power supplies for monitors with LCD backlighting, you can see the high-voltage part. He's an inverter. Its presence is indicated by inscriptions such as “High Voltage” and terminals for connecting lamps. Please note that the voltage supplied to the lamps is over 1000 Volts! It’s better not to touch, much less lick, this part when you turn on the monitor.
Swollen capacitors
These are, of course, electrolytic capacitors in the power supply filter.
This is one of the most common failures of LCD monitors. Capacitors are easily and simply soldered. Sometimes boards have a non-standard capacitor rating, for example 680 or 820 uF x 25 volts. If you encounter swollen capacitors of the same value and they are not in your radio store, do not rush to go around all the radio stores in your city in search of exactly the same value. This is exactly the case when “too much is not harmful.” Any electronics engineer will tell you this. Feel free to set 1000 uF x 25 volts and everything will work fine. It's possible even more.
Due to the fact that the power supply emits heat during operation, which has a detrimental effect on the service life of the capacitors, be sure to install capacitors marked “105C” on the case. Also, after soldering the capacitors, it would not hurt to check the fuse of the secondary circuits, which is often a simple SMD resistor with zero resistance, size 0805, located on the back of the board on the trace side.
Zener diode failure
And one more nuance, at the output of the power supply, in front of the power connector going to the scaler, an SMD zener diode is often installed
If the voltage on it exceeds the rated value, it goes into a short circuit and thereby turns off our monitor through the protection circuits. You can replace it with any suitable voltage rating. Can even be used with leads
After everything is done and repaired, we check the voltage at the power connector that goes to the scaler. All voltages are signed there. We make sure that they coincide with the multimeter readings.
Problems in the high-voltage part of the power supply (inverter)
If possible, first of all, always look for diagrams of the device being repaired. Let's look at the high voltage part of one of the monitors
If you see that the monitor's power supply fuse has blown, it means that the resistance between the monitor's power wires (input impedance) has become very low at some point (short circuit). Somewhere around 50 Ohms or less, which in turn, according to Ohm's law, caused an increase in current in the circuit. Due to the high current, our fuse wire burned out.
If the fuse is in a metal-glass case, we can insert absolutely any fuse into the mount and test the resistance between the pins of the plug in 200 Ohm Ohmmeter mode. If our resistance is zero and up to 50 ohms, then we are looking for a broken radio element that rings to zero or to ground.
The steps will be like this:
We insert the fuse, switch the multimeter to 200 ohms and connect it to the power cord plug. We make sure that the resistance is very small. Next, we are in no hurry to remove the fuse.
So let's look at the diagram to see which radio components we can short out. In the photo, those parts that will need to be checked are highlighted with colored frames. short circuit in the high voltage part
All these procedures for measuring resistance are done in order to call the listed parts one by one. That is, we unsolder and again measure the resistance through the plug. As soon as we get high resistance at the input of the plug, having replaced or removed the defective radio element, we can safely plug the plug into the socket and dig further.
No monitor backlight
What is the difference between LCD-backlit monitors and LED-backlit monitors? In LCD monitors, we use CCFL lamps for backlighting. In Russian, this abbreviation sounds like “cold cathode fluorescent lamp”.
These lamps are located at the top and bottom of the display and illuminate the image.
LED monitors use LEDs for backlighting, which are located either on the sides of the display or behind it.
Now all monitor and TV manufacturers have switched to LED backlighting, as it reduces energy consumption by almost half and is much more durable than LCD backlighting.
If there is no backlight, then the problem may be either the CCFL lamps or the LED strip. If they do not light up at all, the image will be so dim that nothing will be visible on the display. Only a careful inspection of the switched-on monitor under lighting can show that there is still an image. Therefore, if there is no image at all, then the first thing to do is inspect the switched-on monitor under a stream of light. If the image is even slightly visible, then take further measures, either change the lamps, or the problem is with the inverter.
Monitor backlight disappears
Our monitor turns on, works for 5-10 seconds and goes out. This indicates that one of the CCFL display backlight lamps has become unusable. Before this, part of the screen may also blink a little. In this case, the inverter will go into protection, which will manifest itself in automatically turning off the monitor backlight.
In order for us to check the lamps and rule out a defective one, we need to buy a high-voltage capacitor from a radio store. 27 picofarads x 3 kilovolts for 17-inch monitors, 47 pf for a 19-inch monitor and 68 pf for a 22-inch monitor.
This capacitor must be soldered to the contacts of the connector to which the backlight lamp is connected. The lamp itself, of course, must be turned off. By connecting a capacitor to each connector in turn, we ensure that our inverter stops going into protection.The monitor will work, although it will be a little dim.
Of course, rarely anyone does this. The trick is to disable the protection on the PWM chip itself))). To do this, google “remove inverter protection xxxxxxx.” Instead of “xxxxxxx” we put the brand of our PWM chip. Once I turned off the protection on a monitor with a TL494 PWM chip according to the diagram below, soldering a 10 Kilo Ohm resistor. Monique is still working. No complaints).
Without such backlighting, no LCD TV can operate normally, regardless of its brand. We will tell you how you can repair your TV's LED backlight at home using an Lg device as an example, and what you will need for this.
How can you tell if the backlight is broken? Let's assume that the problem with the LCD TV is as follows: it turns on from the remote control, but the screen does not light up (if your TV does not turn on even from the remote control, read about). When pointed at the display flashlight light(i.e. forced illumination is applied), then the image appears. Verdict - the ice driver or similar backlight does not work, perhaps due to the fact that the special lines with soldered LEDs have burned out. You need to disassemble the TV and visually inspect the parts to find a fault.
Attention! You can only open the case of an LCD TV if you have the skills to work with complex devices and a little experience, otherwise it’s better not to risk it.
Remove the back cover For any LG TV, this is not a difficult task, you just need to do everything carefully and without haste: disconnect the legs of the stand and unscrew the mount around the entire perimeter of the product. If the cover does not come off, it means there is a blocking bolt, you should not make any effort, you need to find it and unscrew it.
After removing the back cover, check the output voltage.
If it is normal, we check it voltage ice backlight the screen itself. Its value is only 100V, which indicates a malfunction in the backlight of the LCD TV.
These TVs use a special LED set with lenses that are installed across the entire screen area to provide clear illumination. To get to them and repair the LG TV backlight, you must first remove the matrix.
Disassembling the product
The TV has three main boards - main, T-con and power supply, all of which are clearly visible in the photo.
Removing and disassembling the matrix do it yourself - the work is very painstaking, one careless movement, and you can buy a new TV, so without experience it is better not to undertake repairs. Experts highlight the following main points when disassembling the matrix:
- it is necessary to prepare a work area and two tables on which to lay matrices and scattering films;
- Before starting this work, you should thoroughly wash your hands so as not to accidentally leave traces of dirty fingers on the filters and the matrix itself - this can harm the quality of the image later;
- Special attention should be paid to decoders - one inaccurate movement can lead to a break in the cable.
Subsequent dismantling is carried out in several stages.
Troubleshooting
Now the actual repair of the LED backlight of the TV begins: to do this, you need to carefully unclip all the latches along the contour, remove the plastic frame and remove the diffusing films to expose the LEDs.
U different models LG TVs will have their own set of LED backlights: for LG 32LN541U there are three rows of 7 LEDs, and for LG 32LB582V there are three rows of 6 LEDs.
In all TVs that use such backlighting, the LEDs are connected in series, so if one of them burns out, the entire system stops working. If the LED driver is faulty, then no voltage is supplied to the entire system, and when one of the LEDs burns out, then the voltage flows, but all the efforts of the device to illuminate the system are in vain: even if you supply 200 volts, the circuit is open.
As we can see from the photograph, the backlight consists of 18 LEDs; during measurements, the voltage without load was 140 V, that is, each one accounted for 7.8 V. When we take into account the voltage drop on each strip and the total load, the conclusion will be as follows: this model uses 6V LEDs.
Finding a burnt-out LED is not easy: if there is no burnout at the mounting location, then you need to check each element separately.
Replacing LEDs
Replacing the Lg TV backlight can be a bit of a hassle. Let's say that the test results revealed several faulty LEDs. It is quite difficult to buy a replacement bar - these parts are not supplied to service centers, you can order them on the manufacturer's website, but this is time-consuming and very expensive. So there is only one way - replace individual diodes, although it will not be easy to find them on the radio market. Experts assure that you can buy already soldered ones, but in good working order; after a long search, these are exactly the ones we purchased.
Users should be aware that all planks are glued using double sided tape , so you need to warm them up with a special soldering gun so that the tape comes off. To do this, the bar is fixed in the holder and heated from below with a hairdryer, the tin is melted, and the faulty part is removed. Soldering should be done using exactly the same method to avoid damaging the LED.
Important! All lenses are secured with a compound at the factory, so when removing them you must act very carefully, and each one must then be installed in its original place so as not to disturb the original focusing.
One more nuance: you may come across LEDs whose negative pad is slightly larger size, than the positive one, so you need to trim the contact point in order to solder the diode. This is what a soldered LED looks like:
The fact that the paint is a little damaged is not a problem. We solder the rest of the LEDs in the same way, and Glue the lenses with superglue. And this is a repaired view of the backlight panel assembled and ready for further use:
As we see in practice, there are many specific nuances in repairing the LED backlight of an LG TV matrix, and without knowing them, it is impossible to achieve a positive result.
Final works
When the LG TV system has been completely repaired, before final assembly, we connect the voltage to the strips and check the glow of all LEDs. If everything is fine, then we assemble the TV, performing all operations sequentially and with caution, as during dismantling.
After finishing, it is better not to turn the backlight brightness to maximum, but to limit it to 75% - in this mode, the LEDs operate in normal mode and, according to experts, will last much longer.
We install the TV in its original place, turn it on and enjoy the quality: if there are no extraneous spots of light or dark color anywhere on the screen, it means that the repair was carried out correctly, in compliance with all recommendations. And you can get the most out of your TV by learning how to properly
The most reliable LG TVs of 2018
TV LG 22LH450V
TV LG 49UJ651V
TV LG OLED55C8
TV LG 55LJ622V
TV LG 55UK6100
Once upon a time there was one liquid crystal monitor BENQ FP93G-X, faithfully serving its owner for many years, delighting him with a beautiful image. But a couple of months ago, trouble happened to it - at first it turned on every once in a while, then stopped turning on completely. It will show a picture for a couple seconds and turns off. The diagnosis was disappointing - the CCFL backlight lamps had exhausted their service life and failed. A new monitor with a larger diagonal was purchased as a replacement and the old man was put into storage until better times. But I felt sorry for the hard worker and by searching on the Internet a way was found to revive it - replace the lamp backlight with LED.
As a result of the search, a ready-made kit was found on AliExpress and immediately ordered. I’ll say right away that with this kit only a driver was needed, and the LED strip could be used in some other homemade project.
Delivery and contents of the parcel
Driver test
Before installing it in the monitor, the driver was tested. To do this, I connected it to a 12 volt power supply, and connected the ENA and DIM pins to the power plus through 47 kohm resistors. The driver worked: 
Next, we purchased two meters of this LED strip: 
And connected to the driver instead of the standard strip. A 120 kohm variable resistor was also added to the ENA wire to adjust the brightness of the glow. The driver launched 2 meters of LED strip without any problems. Maximum brightness: 
Minimum brightness: 
I ran the driver like this for a couple of hours - nothing on its board got hot.
Driver installation
Next, the monitor was disassembled; I did not film during disassembly, since this process requires accuracy and instructions for disassembling the LCD monitor can be easily found, for example here
When the CCFL lamps were removed, their examination confirmed the initial diagnosis: 
2 LED strips were glued into the CCF lamp mounting profiles - they fit perfectly in width and good send off I brought the power supply out. Then I reassembled the monitor and applied 12 volts to the new backlight and made sure that the entire monitor screen was evenly illuminated.
Then it was necessary to turn off the high-voltage power supply, which was no longer needed. To do this, fuse FP801 was soldered on one side of the power supply board: 
Through it, a voltage of plus 30 volts was supplied to the inverter, but now it will be used to power the driver.
We glue a scarf made of insulating material with a radiator for a 12-volt Krenka onto a metal base - since 30 volts is a bit too much, we use it to stabilize the voltage: 
We glue the driver onto the scarf, install the Krenka on the radiator, connect the wires to the power supply board, solder the wires from the backlight directly to the driver board: 
The ENA and DIM pins on the monitor power supply board can be easily found with a multimeter.
Install the power supply and connect the driver power: 
We cover everything with a metal screen: 
Final test and conclusions
We assemble the monitor completely and turn it on: 
Works! Upon careful inspection of the image, no flares or color distortions were found.
Pros:
1.Good appearance and careful soldering.
2.Price.
3.Easy to install.
Cons:
1.There are no mounting holes on the driver board.
I'm planning to buy +52 Add to favorites I liked the review +44 +92
Models of LED-backlit TVs dominate the market and deservedly so. In this article we will look at the types of LED backlights on modern TVs and evaluate their effectiveness.
LED TVs
Let's start with the fact that LED TV is not a new type of HDTV . Unlike plasma and OLED TVs, which are made on the basis of emitting technologies, where each pixel is a separate light source, in liquid crystal models, each pixel of the LCD matrix requires lighting (from behind or from the side through a lens system). So LED HDTV models are the same liquid crystal (LCD or LCD) TVs, but they have a built-in light-emitting diode (LED) backlight, which replaces the standard one fluorescent lamps cold cathode (abbreviated CCFL).
2 types of LED backlight according to design: matrix and side
LED backlighting with local dimming. First, televisions with LED backlight, used to illuminate the cells of the LCD matrix " full array"(full array) of LEDs, similar to standard TVs based on backlighting using CCFL lamps. But to change the thickness of TVs downward, the developers abandoned the use of a full array LED LEDs behind the screen by installing the light source bars on the side of the LCD panel. Thus, the distribution of light from LED sources over the entire screen area is carried out using specially shaped LEDs. These LCD TV models are called TV with side or regional LED backlight, which still dominate today.
LED lighting with local dimming system allows you to automatically reduce the brightness or completely turn off individual groups of backlight sources. Most modern LCD TVs with LED backlighting are equipped with a full array of LED sources placed behind the LCD panel. dynamic backlight technology also called local or local dimming. Using local dimming, specific areas of the overall backlight LED array become darker or lighter depending on the brightness and color of the corresponding part of the image on the screen.
The ability to darken a specific area of the screen can reduce the amount of light that passes through the closed pixels of the LCD panel, which has a positive effect on the rendering of blacks, which become darker and more realistic. Because black levels are critical to contrast, the perception of depth on black surfaces, full-color images become more vibrant and clear. Local dimming technology has the only drawback - the effect of local dimming, which is formed when part of the light from brighter zones leaks into neighboring darker ones, which subsequently brightens at the border dark color. It is quite difficult to notice the clouding effect on most models, since the disadvantage is directly related to the number of local dimming zones behind the screen, and manufacturers do not always provide such information.
When using standard backlighting using CCFL lamps and in most LCD TVs with edge LED backlighting, all backlight sources brighten or dim at the same time (the so-called " global dimming"), but among Samsung and LG TV models there are rarely displays with side LED backlighting, which can also work on the principle of local dimming (“precision dimming” for Samsung and “LED Plus” for LG). To put it simply, this is a local dimming sham.
Thin models with side LED backlight Of course, they suffer from uneven screen illumination, but not everyone. Main feature of TVs with side LED backlighting– thin body, therefore it is difficult to ensure uniform distribution luminous flux across the entire screen plane. When purchasing a TV, play an image of the white surface on the edge-lit LED display screen to check that there are no brighter areas around the edges of the screen. Likewise, when the screen is filled with a black field, the edges should not appear lighter (gray).
It is also worth noting that LED backlighting, regardless of the type, does not improve the viewing angles of the LCD panel. The black level drops when using LED backlighting and possibly shifting the viewing angle by 1-2 meters to the left or right.
We must not forget about the energy efficiency of LED backlighting. Of course, the consumption of any model is significantly affected by the size of the screen and the brightness of the backlight sources. LCD TV models of both types of LED backlighting are much more energy efficient compared to plasma models.
LED backlights for LCD displays are divided into categories according to the following criteria:
- glow color: white or RGB;
- lighting uniformity: static or dynamic;
- design: matrix or side (this is described in more detail above)
RGB backlighting is used to fine-tune the light spectrum. In addition, additional compensation for changes in the emission spectrum of LEDs over time is often applied. LED TVs with RGB LED backlighting light up different areas of the screen depending on the color of the picture. Colored backlighting provides enhanced contrast and deep blacks, as demonstrated by many Sony LED TVs.
Edge LED: Better Color Rendering
Sony in its new flagship TV models - for example, the W905 line - uses Triluminos technology. The LED backlight (Edge LED) built into the frame of the TV on all sides of the screen is complemented by so-called quantum dots - fragments of a semiconductor several hundred atoms in size that emit light in a strictly specified range. Triluminos technology is designed to minimize color distortion and provide enhanced red and green tones. This will allow you to achieve an extremely uniform and natural image with a significantly wider color gamut. Tests of the first devices with Triluminos support did not disappoint us: the color gamut of the Sony KDL-46W905A model is comparable to that of organic light-emitting diode (OLED) solutions and is unattainable for LED-backlit LCD TVs. The W805 and W605 series devices, which also went on sale this year, do not use Triluminos, making their cost significantly lower. In the future, manufacturers will be able to completely abandon LED backlighting in favor of quantum dots.
OLED TVs: brightness and color at their best
TVs with OLED screens have already reached stores, and developers have rushed to release new models with concave displays. Last year, LG planned to introduce a 55-inch OLED TV to the market, but it only went on sale this summer. In Russia, the 55EM9600 model and its improved analogue 55EM9700 will cost the buyer 500,000 rubles. In addition, the device is sold in Europe, the USA and some other countries.
Advantages of OLED TVs: it is not a type of backlight, but a different technology
- accurate color reproduction
- greater brightness margin compared to other technologies
- high contrast compared to LCD models (another imaging technology).
- absence of an LCD matrix and LED backlight - their place was taken by a matrix made of light-emitting organic diodes.
Samsung and LG independently developed OLED TVs with concave screens (Curved OLED). This design is designed to minimize distortion at the edges of the image and increase detail. New items are still available in limited quantities in South Korea, USA and some European countries. The 55-inch model Samsung KN55S9C is priced by the manufacturer at $9,000 (300,000 rubles).
Of particular interest is also Multi-View technology, implemented in many models of OLED TVs with both flat and concave screens. Due to their exceptionally fast response time, such devices allow you to simultaneously show two or four programs in high definition (Full HD) or two different films in 3D format. Shutter glasses are used to separate the image. Each viewer can use the controls located on the glasses to select an individual program for viewing. At the same time, thanks to the built-in headphones, playback of the soundtrack corresponding to the film is ensured.