Replacing fluorescent backlights in the monitor with LED ones. Security Information Portal

Without getting any results, I had to disassemble the monitor further. I removed the metal and plastic “cases” from the matrix, carefully took out the display and placed it on a flat surface and covered it with a cloth to protect it from dust. Under the display there were all sorts of films for uniform dispersion of light and something similar to glass, to which the backlight itself is attached.
And now I’ve already removed the lamps, almost all of them were burnt near the electrodes, and one even cracked and turned yellow because of this.
Searching for new backlight lamps on the Internet did not yield any results. desired results, and the purchase itself, it seemed to me, would be expensive and time-consuming. Without thinking long about how to solve the problem, a good idea came to me. Namely, remove the lamps and stick an LED strip instead. Walking around the market, I bought a meter of cold tape white with the most dense placement of LEDs:
The tape fit perfectly - both width and length. At a voltage of 12 volts, the tape burns very brightly and even blinds:
The current consumption of both tapes was slightly more than 200 mA, which made it possible to use a simple KREN8B stabilizer (12V 1.5A).

Some installation problems

I took power for the crank from the monitor’s power supply (15V), but as it turned out, this was not enough and the voltage dropped to 9V at the output of the stabilizer. Since the monitor always stands in one place and there is a free socket, I took the power from a 16V 0.9A mains power supply. Now everything is back to normal with the voltage, but this KREN8B gets quite hot. In 5 minutes from +26 to +60 with a small radiator. The solution to this problem was 2 parallel soldered 20 Ohm resistors, which are placed after the stabilizer. The temperature still didn’t suit me, so I moved Krenka to a larger radiator and attached the circuit to back cover monitor.

The result of replacing the backlight in the monitor

All colors and shades are reproduced perfectly by the monitor. I read somewhere that the eyes get tired faster from LED backlighting than from regular gas-discharge backlighting. But while I was writing this text, it was quite pleasant to look at the screen and my eyes showed no signs of fatigue. In general, an inexpensive repair of the backlight cost 200 rubles (tape + KREN8B).. See you soon, Vitaly Yakovenko was with you ( BFG5000).

Discuss the article REPLACEMENT OF FLUORESCENT BACKLIGHT LAMPS IN THE MONITOR WITH LED

Hi all!

Sometimes, during renovation LCD backlight , difficulties arise in acquiring the necessary luminescent (CCFL ) lamps . In such cases, you can convert the lamp backlight to LED. Such a modification is not so difficult, and special problems does not occur with spare parts.

In this article I offer you the principle of such a reconstruction in the form of some instructions.

Replacement steps LCD backlight to LED:

Disassemble the monitor or TV. After removing the plastic case, carefully disconnect the wires from the board, remove the metal frame from the LCD module and remove the matrix. You need to be especially careful with the matrix so as not to damage the fragile connecting cables. If everything is done correctly, then full access to the electronic board, power inverter and backlight elements will be open.

2. Disconnect the pencil cases from lamps from the matrix or the lamps themselves, if they are installed without canisters.

3. Disconnect old lamps and recycle them. With elements CCFL You also need to be extremely careful, because they contain mercury.

4. We proceed to the replacement stage. First you need to purchase an LED strip, preferably with a reserve so that it is enough to replace all the lamps (measure the length of the lamp and multiply by their number). It should be as narrow as possible and with at least 120 LEDs per meter. To make the backlight more pleasing to the eye, it is better to take LEDs with a white glow.

5. The strip with LEDs must be glued with double-sided tape to where the lamps were. Next, wires from old lamps are soldered onto the contact terminals of the strips and insulated with hot-melt adhesive. You can immediately check the functionality of this design by connecting the wires to external source nutrition.

6. Now you need to connect the backlight to the power board of the monitor or TV. To do this, you need to find jumpers marked “12 V” and solder the backlight wires there, observing the polarity accordingly. Reassemble the monitor in reverse order and enjoy your invention.

Backlight V in this case will work when the device is connected to the network.

To control the backlight and bring it into normal mode, you will have to work hard. The wires leading to the LEDs must be powered in such a way that it is possible to turn on the backlight when you press the on/off buttons and adjust its brightness. There are 2 options for this:

1.We independently create a power supply circuit and adjust the backlight brightness:

• On the power supply chip of a monitor or TV, we look for a plastic box (connector) with wires coming out of it, where each socket is labeled on the board.

• Here we are interested in the “DIM” output. It will be responsible for sending a signal to turn it on/off and adjust the brightness by changing the duty cycle in the PWM controller. The duty cycle indicator of the pulses changes until the desired brightness level is established, and the limit values ​​will correspond to switching on and off.

• Now we need an N-channel field effect transistor(field worker) anyone. Wires from the LED strip with a minus are soldered to its drain (Drain), the common wire from the backlight is also connected to the source (source), and the gate (gate) is connected through a 100-200 Ohm resistor and any wire is connected to the “DIM” terminal.

• We still have wires from the backlight with a plus, we bring them to the +12V power supply on the microcircuit and solder them.

• Now we install the backlight in its rightful place and assemble the monitor in reverse order. Do not forget about caution and accuracy when handling the matrix and filters so that dust does not get in and the cables are not damaged. That's it, you can use it.

1. The second way, more expensive but convenient, is to buy a ready-made LED backlight with your own inverter :

• Again, pay attention to the plastic connector and the DIM pin (brightness) and the on/of pin (it’s better to use the pinout).

• Using a multimeter, we determine the places on the control unit of old lamps from which the signal for brightness and on/of comes.

• Now solder the wires to the found places inverter new LED backlight .

• Also, it is better to unsolder the jumpers from the inverter power supply of the old lamps so that the backlight can be regulated by the new inverter.

• Good day!

  In this post, I would like to consider such a sore LCD monitors, like failed backlight lamps, try to figure out why this is happening, and change them accordingly. If you are interested, I ask you to follow the green man.
  P.S.
  Below the cut there are 27 photos

  -Dear people, I apologize in advance for the quality of the subsequent photos, I took pictures on a toaster....

  -Also, I want to note that monitors in their own way basic structure don’t differ much, so don’t be alarmed if you suddenly don’t find screws or anything else in the place shown in the photo, they’re somewhere nearby...

  So, we have a monitor that works in almost romantic, red-pink tones. The operating time of such a monitor is unpredictable... but as a rule it does not exceed 2-3 hours, after which your eyes are given time to rest and your brain to think about the issues of existence.

  

  The problem is a failed monitor matrix backlight lamp, but why did this happen?
  There are many reasons for this situation:
  - manufacturing defect,
  - shorting the metal parts of the lamp to the metal frame of the matrix,
  - physical damage, etc.

  But let's delve a little into the theory.

  LCD matrices work through transmission, that is, the monitor must have a light source that illuminates the matrix through. The quality of the monitor depends quite significantly on the light source. For stationary LCD displays and TVs, direct backlighting is usually used, when light sources (lamps or LEDs) are distributed over the entire panel area. ©

  But why does he continue to work then? and such a short period of time?
  It's simple.
  It is worth noting that monitors most often use 2 blocks of 2 lamps ( top and bottom of the monitor), which should distribute the light evenly along the light guide under the matrix.
  If one or more lamps fail, the rest continue to work. But the inverter ( which powers them) is a smart thing, and if he “sees” that something is wrong with one or more of his charges, he decides to stop his work so as not to cause harm.

  

  Well, let's get down to business, shall we?
  We start by disconnecting all the cables from the inverter unit and the monitor controller,

  

  

  

  Filming back panel with power supply and controller

  

  Removed? great... What we see, in numbers 1 We have marked the power wires going to the treasured lamps.
  2 - a train going to our matrix.
  The asterisks indicate places that need to be picked out so that disassembly can continue.

  We are removing the panel on the left for now, we don’t need it now
  
  

  

  

  And again we disassemble our “matryoshka”
  
  

  Great, we're almost halfway there,
  Now let's explain:
  5 -our matrix (the same thing with numbers 640x480~1920x1080)
  6 -signal decoder connected to the matrix by a row/column data line
  7 -light guide with light filters

  Next, we again delve into the “wilds of the monitor” and remove the plastic frame around the perimeter...
  
  

  
  Under the black frame there are 2 thin films lying on top of each other, and under them there is a light guide.
  8 -light filter
  9 -polarizing film
  10 -light guide
  
  

  Now we take out the large acrylic thing ( 10 ) and finally we can see the heroes of the occasion...
  Those assholes who made us come this far ( 11 )

  

  Gentlemen. I present to your attention broken, faulty backlight lamps!
  Speaking of lamps.
  Did you know:
  

  that LCD panels use CCFL lamps, which in Russian means cold cathode fluorescent lamp. Its principle is almost the same as hot (in common parlance “fluorescent lamps”). The only difference is that to obtain plasma in a hot one, the initial heating of the cathodes is used, and in a cold plasma the plasma is obtained due to high voltage applied to the cathodes. Next, the plasma, which has an ultraviolet radiation spectrum, hits the phosphor, the white coating that you see through the flask, and is converted into visible radiation (white light) ©

  

  As we can see, they really burned out. (the “black marks” around the cathodes hint at this)
  
  

  We unscrew them, having first pulled out the reflective backing ( or maybe you don’t have to do this on your monitor)

  

  

  ... and swap them ( I want to note that you should be careful, because they are quite fragile. I also advise you to securely fasten the wires and keep a vigil so that there is no breakdown in the future. We isolate everything to the maximum!)

  

  Now we will return our lamps to their place, screw them on, return the reflective thing and put the light guide in place.
  We connect - everything works! ( Before this it also worked, but not correctly, only 1.5 lamps were on, I didn’t bother to capture this action in disassembled form. I repent)

  

  Well... the hardest part is over, all that remains is to put everything back together.
  Let's get started.
  
  

  We return the films to their place, cover them with a plastic frame and place our matrix on top, fixing it with a metal frame.
  (Here we should not forget about such a thing as dust... before assembling everything, it’s worth blowing air through all components of the monitor, it won’t take long, but it will affect the image quality)

  

  We turn it over and return the last “detail” to its place.

  

  Connect to the “stand” and rejoice!
  Everything works, no traces of uneven illumination were noticed,

  

  The flight is normal.

  

  Fin.
  _______________________________________________________________________________

  What would you like to say in conclusion?

  0 It turns out that replacing the lamps yourself is not so difficult, if only you had the desire.
  You can also experiment and replace the lamps with LED strip. But you need to remember that the LED strip does not give a completely uniform light + on top of everything, it’s very possible that 1 or more LEDs will burn out/become a little dimmer, and then the backlight will become uneven. Also, don’t forget about color temperature LEDs

  1 .When replacing lamps, you need to know exactly their dimensions; I used this table as a guide.

  

  2 . Why did I decide to write this article?
  Faced with monitor repair for the first time, I went into "some search engine", and did not see detailed instructions...
  No, I’m not saying that I didn’t find them, they were there, but they seemed incomplete to me, so it was decided to collect this material and post it here. You never know who will find it useful...

  3 .Links to similar/used/additional materials:
  cheklab.ru/archives/2534 (good article about the device various types monitors)
  radiokot.ru/lab/hardwork/30 (replacement of backlight bulbs + some background information)
  habrahabr.ru/post/182772 (we revive the monitor if there are no new lamps at hand)
  radioskot.ru/publ/remont/zamena_ljuminiscentnykh_lamp_podsvetki_v_monitore_na_svetodiodnye/4-1-0-594 (successful replacement of lamps with LED strip)
  www.yaplakal.com/forum2/topic471720.html (almost successful replacement of lamps with LED strip)

  4 P.S.
  If Habra residents are interested in posts about the repair and restoration of equipment, then I will be happy to share the material I have accumulated.

  Time passes unnoticed and seemingly recently purchased equipment is already breaking down. So, having worked their 10,000 hours, the lamps of my monitor (AOC 2216Sa) gave a long life. At first, the backlight did not turn on the first time (after turning on the monitor, the backlight turned off after a few seconds), which was solved by turning the monitor on/off again; over time, the monitor had to be turned off/off 3 times, then 5, then 10, and at some point it could not turn on the backlight, regardless of the number of attempts to turn it on. The lamps brought to the light of day turned out to have blackened edges and were legally thrown into scrap. An attempt to supply replacement lamps (new lamps were purchased suitable size) was not successful (the monitor was able to turn on the backlight several times, but quickly went into on-off mode again) and finding out the reasons for what the problem could be in the electronics of the monitor led me to the idea that it would be easier to assemble your own monitor backlight using LEDs than repair the existing inverter circuit for CCFL lamps, especially since there have already been articles on the Internet showing the fundamental possibility of such a replacement.

  Disassembling the monitor

  Many articles have already been written on the topic of disassembling a monitor; all monitors are very similar to each other, so in brief:
  1. Unscrew the monitor delivery mount and the only bolt at the bottom that holds the back wall of the case
  
  
  2. At the bottom of the case there are two grooves between the front and back housings, into one of which we insert a flat-head screwdriver and begin to remove the cover from the latches along the entire perimeter of the monitor (simply by carefully turning the screwdriver around its axis and thereby lifting the housing cover). There is no need to exert excessive effort, but it is difficult to remove the case from the latches only the first time (during the repair I opened it many times, so the latches began to be removed much easier over time).
  3. We have a view of the installation of the internal metal frame in the front of the case:
  
  
  We take out the board with the buttons from the latches, take out (in my case) the speaker connector and, bending the two latches at the bottom, take out the inner metal case.
  4. On the left you can see 4 wires connecting the backlight lamps. We take them out by squeezing them slightly, because... To prevent it from falling out, the connector is made in the form of a small clothespin. We also remove the wide cable going to the matrix (at the top of the monitor), squeezing its connector on the sides (since the connector has side latches, although this is not obvious at first glance at the connector):
  
  
  5. Now you need to disassemble the “sandwich” containing the matrix itself and the backlight:
  
  
  There are latches along the perimeter that can be opened by lightly prying with the same flat screwdriver. First, the metal frame holding the matrix is ​​removed, after which you can unscrew three small bolts (a regular Phillips screwdriver will not work due to their miniature size, you will need a particularly small one) holding the matrix control board and the matrix can be removed (it is best to place the monitor on a hard surface, such as a table covered with the fabric facing down, unscrew the control board, place it on the table, unfolding it through the end of the monitor, and simply lift the backlit case, lifting it vertically upward, and the matrix will remain lying on the table. It can be covered with something so as not to gather dust, and assembled exactly the opposite way. order - that is, cover the matrix lying on the table with the assembled case with backlight, wrap the cable through the end to the control board and, screwing the control board, carefully lift the assembled unit).
  The matrix is ​​obtained separately:
  
  
  And the backlit block separately:
  
  
  The backlit unit is disassembled in the same way, only instead of a metal frame, the backlight is held by a plastic frame, which simultaneously positions the plexiglass used to diffuse the backlight light. Most of the latches are located on the sides and are similar to those that held the metal frame of the matrix (they open by prying them off with a flat-head screwdriver), but on the sides there are several latches that open “inward” (you need to press on them with a screwdriver so that the latches go inside the case).
  At first I remembered the position of all the parts to be removed, but then it turned out that it would not be possible to assemble them “wrongly” and even if the parts look absolutely symmetrical, the distances between the latches on different sides metal frame and fixing protrusions on the sides of the plastic frame holding the backlight will not allow them to be assembled “wrongly”.
  That's all - we disassembled the monitor.

  LED strip lighting

  At first, it was decided to make the backlight from an LED strip with white LEDs 3528 - 120 LEDs per meter. The first thing that turned out to be is that the width of the tape is 9 mm, and the width of the backlight lamps (and the seat for the tape) is 7 mm (in fact, there are backlight lamps of two standards - 9 mm and 7 mm, but in my case they were 7 mm). Therefore, after examining the tape, it was decided to cut 1 mm from each edge of the tape, because this did not affect the conductive paths on the front part of the tape (and on the back, along the entire tape, there are two wide power cores, which will not lose their properties due to a decrease of 1 mm over a backlight length of 475 mm, since the current will be small). No sooner said than done:
  
  
  In the same way, the LED strip is carefully trimmed along its entire length (the photo shows an example of what happened before and what happened after trimming).
  We will need two strips of 475 mm tape (19 segments of 3 LEDs per strip).
  I wanted the monitor backlight to work the same way as the standard one (i.e. it was turned on and off by the monitor controller), but I wanted to adjust the brightness “manually”, as on old CRT monitors, because This is a frequently used function, and I got tired of navigating through on-screen menus pressing several keys every time (on my monitor, the right-left keys do not adjust the monitor modes, but the volume of the built-in speakers, so the modes had to be changed through the menu every time). To do this, I found a manual for my monitor on the Internet (for those who need it, it is attached at the end of the article) and on the page with the Power Board, according to the diagram, +12V, On, Dim and GND were found that are of interest to us.
  
  
  On - signal from the control board to turn on the backlight (+5V)
  Dim - PWM backlight brightness control
  +12V turned out to be far from 12, but somewhere around 16V without backlight load and somewhere around 13.67V with load
  It was also decided not to make any PWM adjustments to the backlight brightness, but to power the backlight DC(at the same time, the issue is resolved that on some monitors the PWM backlight does not work very well high frequency and for some this makes their eyes a little more tired). In my monitor, the “native” PWM frequency was 240 Hz.
  Further on the board we found contacts to which the On signal is supplied (marked in red) and +12V to the inverter unit (the jumper that must be removed to de-energize the inverter unit is marked in green). (photo can be enlarged to see notes):
  
  
  The LM2941 linear regulator was used as the basis for the control circuit, mainly because at a current of up to 1A it had a separate On/Off control pin, which was supposed to be used to control the backlight on/off with the On signal from the monitor control board. True, in LM2941 this signal is inverted (that is, there is voltage at the output when the On/Off input is zero potential), so we had to assemble an inverter on one transistor to match the direct On signal from the control board and the inverted input of LM2941. The scheme does not contain any other excesses:
  
  
  The output voltage for LM2941 is calculated using the formula:

  Vout = Vref * (R1+R2)/R1

  Where Vref = 1.275V, R1 in the formula corresponds to R1 in the diagram, and R2 in the formula corresponds to a pair of resistors RV1+RV2 in the diagram (two resistors were introduced for smoother brightness adjustment and reducing the range of voltages regulated by the variable resistor RV1).
  I took 1kOhm as R1, and the selection of R2 is carried out according to the formula:

  R2=R1*(Vout/Vref-1)

  The maximum voltage we need for the tape is 13V (I took a little more than the nominal 12V so as not to lose brightness, and the tape will survive such a slight overvoltage). Those. maximum value R2 = 1000*(13/1.275-1) = 9.91 kOhm. The minimum voltage at which the tape still glows at least somehow is about 7 volts, i.e. minimum value R2 = 1000*(7/1.275-1) = 4.49 kOhm. Our R2 consists of a variable resistor RV1 and a multi-turn trimmer resistor RV2. The resistance of RV1 is 9.91 kOhm - 4.49 kOhm = 5.42 kOhm (we select the closest value of RV1 - 5.1 kOhm), and RV2 is set to approximately 9.91-5.1 = 4.81 kOhm (in fact, it is best to first assemble the circuit, set the maximum resistance of RV1 and measure the voltage at at the LM2941 output, set the resistance RV2 so that the output has the desired maximum voltage(in our case about 13V).

  Installation of LED strip

  Since after cutting the tape by 1 mm, the power conductors were exposed at the ends of the tape, I pasted electrical tape (unfortunately, not blue but black) onto the body in the place where the tape will be glued. The tape is glued on top (it is good to warm the surface with a hairdryer, because the tape sticks much better to a warm surface):
  
  
  Next, the back film, plexiglass and light filters that lay on top of the plexiglass are mounted. Along the edges I supported the tape with pieces of eraser (so that the edges on the tape did not come off):
  
  
  After that, the backlight unit is assembled in the reverse order, the matrix is ​​installed in place, and the backlight wires are brought out.
  The circuit was assembled on a breadboard (due to simplicity, I decided not to wire the board), and was fastened with bolts through holes in the back wall of the metal monitor case:
  
  
  
  
  Power and control signal On were supplied from the power supply board:
  
  
  The estimated power allocated to the LM2941 is calculated using the formula:

  Pd = (Vin-Vout)*Iout +Vin*Ignd

  For my case, it is Pd = (13.6-13)*0.7 +13.6*0.006 = 0.5 Watt, so it was decided to make do with the smallest radiator for the LM2941 (placed through a dielectric pad since it is not isolated from the ground in the LM2941).
  The final assembly showed that the design was fully functional:
  
  
  Among the advantages:

  • Uses standard LED strip
  • Simple control board
  Disadvantages:
  • Insufficient backlight brightness in bright daylight (the monitor is placed in front of a window)
  • The LEDs in the strip are not spaced closely enough, so small cones of light from each individual LED are visible near the top and bottom edges of the monitor
  • The white balance is a little off and goes slightly greenish (most likely this can be solved by adjusting the white balance of either the monitor itself or the video card)
  Quite a good, simple and budget option for repairing the backlight. It’s quite comfortable to watch movies or use the monitor as a kitchen TV, but it’s probably not suitable for everyday work.

  Adjusting brightness using PWM

  For those Habro residents who, unlike me, do not remember with nostalgia the analogue brightness and contrast control knobs on old CRT monitors, you can make control from the standard PWM generated by the monitor control board without moving any additional controls outside (without drilling the monitor body). To do this, it is enough to assemble an AND-NOT circuit on two transistors at the On/Off input of the regulator and remove the brightness control at the output (set the output voltage to constant 12-13V). Modified scheme:
  
  
  The resistance of the trimming resistor RV2 for a voltage of 13V should be around 9.9 kOhm (but it is better to set it exactly when the regulator is on)

  More dense LED backlight

  To solve the problem of insufficient brightness (and at the same time uniformity) of the backlight, it was decided to install more LEDs and more often. Since it turned out that buying LEDs individually is more expensive than buying 1.5 meters of strip and desoldering them from there, a more economical option was chosen (desoldering LEDs from the strip).
  The 3528 LEDs themselves are placed on 4 strips 6 mm wide and 238 mm long, 3 LEDs in series in 15 parallel assemblies on each of the 4 strips (the layout of the boards for the LEDs is included). After soldering the LEDs and wires, the following is obtained:
  
  
  
  
  The strips are laid in twos at the top and bottom with wires to the edge of the monitor at the joint in the center:
  
  
  
  
  The nominal voltage on the LEDs is 3.5V (range from 3.2 to 3.8 V), so an assembly of 3 series LEDs should be powered with a voltage of about 10.5V. So the controller parameters need to be recalculated:
  
  
  The maximum voltage we need for the tape is 10.5V. Those. maximum value R2 = 1000*(10.5/1.275-1) = 7.23 kOhm. The minimum voltage at which the LED assembly still glows at least somehow is about 4.5 volts, i.e. minimum value R2 = 1000*(4.5/1.275-1) = 2.53 kOhm. Our R2 consists of a variable resistor RV1 and a multi-turn trimmer resistor RV2. Resistance RV1 is 7.23 kOhm - 2.53 kOhm = 4.7 kOhm, and RV2 is set to approximately 7.23-4.7 = 2.53 kOhm and adjusted to assembled circuit to obtain 10.5V at the output of LM2941 at maximum resistance RV1.
  One and a half times more LEDs consume 1.2A of current (nominally), so the power dissipation on the LM2941 will be equal to Pd = (13.6-10.5)*1.2 +13.6*0.006 = 3.8 Watt, which already requires a more solid heatsink for heat removal:
  
  
  We collect, connect, we get much better:
  
  
  Advantages:
  • Fairly high brightness (possibly comparable, and perhaps even superior to the brightness of the old CCTL backlight)
  • The absence of light cones at the edges of the monitor from individual LEDs (LEDs are located quite often and the backlight is uniform)
  • Still a simple and cheap control board
  Flaws:
  • The issue with the white balance, which goes into greenish tones, has not been resolved
  • LM2941, although with a large heatsink, gets hot and heats everything inside the case

  Control board based on step-down regulator

  To eliminate the heating problem, it was decided to assemble a brightness controller based on a Step-down voltage regulator (in my case, an LM2576 with a current of up to 3A was chosen). It also has an inverted On/Off control input, so for matching there is the same inverter on one transistor:
  
  
  Coil L1 affects the efficiency of the converter and should be 100-220 µH for a load current of about 1.2-3A. The output voltage is calculated using the formula:

  Vout=Vref*(1+R2/R1)

  Where Vref = 1.23V. For a given R1, you can obtain R2 using the formula:

  R2=R1*(Vout/Vref-1)

  In calculations, R1 is equivalent to R4 in the circuit, and R2 is equivalent to RV1+RV2 in the circuit. In our case, to adjust the voltage in the range from 7.25V to 10.5V, we take R4 = 1.8 kOhm, variable resistor RV1 = 4.7 kOhm and trimming resistor RV2 at 10 kOhm with an initial approximation of 8.8 kOhm (after assembling the circuit, it is best to set its exact value by measuring the voltage at the output of LM2576 at maximum resistance RV1).
  I decided to make a board for this regulator (the dimensions did not matter, since there is enough space in the monitor to mount even a large board):
  
  
  Control board assembly:
  
  
  After installation in the monitor:
  
  
  All assembled:
  
  
  After assembly everything seems to work:
  
  
  Final option:
  
  
  Advantages:

  • Sufficient brightness
  • Step-down regulator does not heat up and does not warm up the monitor
  • There is no PWM, which means nothing blinks at any frequency
  • Analogue (manual) brightness control
  • No restrictions on minimum brightness (for those who like to work at night)
  Flaws:
  • The white balance is slightly shifted towards green tones (but not much)
  • At low brightness (very low), unevenness in the glow of LEDs of different assemblies is visible due to the spread of parameters

  Improvement options:

  • White balance is adjustable both in the monitor settings and in the settings of almost any video card
  • You can try installing other LEDs that will not noticeably disrupt the white balance
  • To eliminate the uneven glow of LEDs at low brightness, you can use: a) PWM (adjust the brightness using PWM by always applying the rated voltage) or b) connect all the LEDs in series and power them regulated source current (if you connect all 180 LEDs in series, you will need 630V and 20mA), then the same current must pass through all the LEDs, and each will have its own voltage drop, the brightness is regulated by changing the current and not the voltage.
  • If you want to make a PWM-based circuit for LM2576, you can use a NAND circuit at the On/Off input of this Step-down regulator (similar to the above circuit for LM2941), but it is better to put a dimmer in the gap of the negative wire of the LEDs via a logic-level mosfet

  Hi all!

  I have a lot of information on the website on repairing and replacing LED backlights, and on repairs lcd backlight And replacement CCFL lamps no information.

  Well, this article will, in some way, correct this shortcoming.

  Everything you need to know about backlighting before you climb inside your monitor or TV.

  1.The first and main signs of problems with the lamp:

  — the image has acquired a constant or periodic pink tint;

  — the backlight goes out completely after switching on or after a while, while the sound remains and the picture can be viewed if you bring the lighting device to the monitor. A similar symptom may indicate problems with the inverter, which is responsible for transmitting the signal to the lamps.

  1. Quantity lamps in LCD on monitors there are usually at least 4, and on TVs it can be one or several. This depends on many factors: the age of the device, its diagonal, etc.

  2. Before replacing, you need to make sure that the new light elements fit the parameters. For this purpose, there are tables on the correspondence of lamps to display diagonals. Better to follow it. It is possible that you will be able to install a lamp with a length difference of 1-2 mm, but this will take more time and effort.

  3. The process of replacing lamps for a beginner will take approximately 3-4 hours if you follow the instructions and do not experiment.

  4. Caution doesn't hurt! When working with an inverter, be extremely careful, because its voltage output is approximately 1000V. And when you change the lamps, try not to break them, because... they are very fragile and contain mercury vapor.

  Process replacing lamps lcd backlight TVs and monitors.

  For the lamp replacement procedure itself, you will need:

  - a well-cleaned room and a clean surface;

  — rubber gloves (medical gloves are ideal);

  - a sharp thin knife (for example, a stationery knife);

  — heat-shrinkable tubes;

  - a set of screwdrivers.

  So, you need to get to the lamps. At first monitor (TV) must be freed from the protective plastic box - unfasten it from the narrow panel, which is located along the perimeter of the screen in front. Then carefully, by unscrewing a few screws, remove the entire LCD module from the metal frame.

  Now begins the most difficult work that requires patience and accuracy - disassembling the electronic panel and module into components. To remove the matrix (and you will have to remove it), you will need to arm yourself with tweezers and peel off protective film from the electronic board (matrix decoder). This must be done carefully, because the thickness of the decoder is only 1 mm, and it is connected to the matrix by the thinnest data lines. If you try to cut off the film or pull harder, a breakdown will inevitably occur, after which it will be impossible to restore the functionality of the element.

  
  

  When removing the matrix, like other elements, you need to wear gloves, because finger stains will subsequently be reflected on the image. In the same way, dust and other debris will make themselves known, so you should minimize their contact with open elements.

  After removing the matrix, a set of filters and a light guide, where the lamps are located, will come into view. They can be located in pairs in pencil cases at the top and bottom of the monitor or in horizontal rows along the entire perimeter of the screen. In rare cases it may not be necessary full analysis LCD module, because sometimes cases with lamps are removed more accessible ways. But all this can be learned only in the process of work.

  When you get to the lamps, you can immediately notice the faulty ones - blackened cathodes will tell about this. But if the lamps visually look the same, then you will have to figure out which one to change. The method of replacing a working (preferably new) lamp will be the simplest. If this method cannot be implemented, then using a special device you can create a resistance of approximately 1 kOhm-2 W through an inverter.

  After replacing the lamps, perform the reverse process - collecting all the parts of the device into the original design. Assemble carefully to avoid fingerprints, dirt, dust and foreign objects. If everything is done correctly, the TV or monitor will work normally.

  
  

  Replacing the standard CCFL lamp with an LED one.

  Devices with an LCD system use CCFL lamps or, in our opinion, fluorescent lamps, which glow not by heating the cathodes, but by applying voltage to them. That's why they are called cold cathode lamps. Such a light source should ideally be replaced with an identical one. But we will briefly look at replacing it with an alternative LED lighting system:

  • First, you will need to disassemble the device according to the scheme described above.

  • Remove the lamps and remove the inverter.

  • Buy LED strip the right size and better than white glow. You can find ready-made designs with a set of LEDs and a control device for them.

  • The LED strip is glued with double-sided tape to the place where the fluorescent lamp was.

  • Wires are connected to this design, which are brought out onto the board and soldered to where the 12V power supply is indicated.

  • The functionality of this circuit is checked and the monitor or TV is assembled.

  This method has disadvantages and advantages. CCFL lamps definitely illuminate brighter and more evenly (better for the eyes), but LED strip is more affordable and less expensive. This backlight is not adjustable. Although you can try to create more on your own complex circuit control, which will take more than one hour (maybe a day) or you will spend money and buy a ready-made design with a controller. But, perhaps, the main advantage of LED backlighting is significant energy savings and durability (120 years!!).