LCD display backlight. Kit for replacing CCFL lamps in an old monitor with LEDs. Description of the circuit diagram

I also wanted to ask you about the “PMS” contact, which goes from the main board to the power supply or vice versa, from the power supply to the main board. Can't define his role?
I'm interested in this because I also want to turn it off. I will hang the monitor on a swivel bracket and I want to power it from a standard TFX power supply from a mini case, in which a new computer for my parents will be assembled (with not very new components, with DDR3L memory and a 3rd generation Intel processor :). Today I conducted an experiment, supplied 5V, 12V and minus from the floppy drive connector from the computer power supply. The monitor worked fine and surprisingly even turned on and off using the power button (I assumed that the PMS sends a signal to the power supply to turn off the power to the inverter or the inverter and the main board at the same time). It’s just that the monitor will hang above the bedside table and there’s not enough space there, so it’s much easier for me to power it from the power supply, especially since I built a two-phase switch into the power supply that turns off zero and phase at the same time (that is, the computer is no longer needed unplug). And if you run a separate 220V cord to the monitor, then there are more wires, plus more hassle with turning it on/off, and the efficiency of the power supply will be slightly lower (the total energy consumption when powered from the computer power supply will decrease by ~5-10 watts). Power supply with "GOLD" certificate, Sea Sonic Electronics SSP-300TGS Active PFC 300W. Therefore, I need to know what the “PMS” signal does, wouldn’t its absence on the monitor’s power supply be critical?

I also conducted an experiment with "PMS" today. 2.794 volts are supplied to this contact and only when the monitor is running. If the monitor goes to sleep or is turned off via the button on the front panel, then “PMS” immediately drops to zero. It also turned out that the first coil produces 5 volts 1.5 amperes, and the second produces simultaneously 12 volts 1.2 amperes (to power the main board) and 12 volts 3 amperes (to power the inverter). That is, whenever the monitor is turned off or asleep, 12 volts disappear from both lines, and 5 volts are supplied all the time while the monitor is plugged in and the main switch supplies 220 volts to the power supply (apparently 5 volts also goes as power to the main board and at the same time they are needed to wake up the monitor from standby mode).
So most likely “PMS” still comes from the main board to the power supply and is needed to launch a high-power coil, but I still want to know the opinion of an expert, since I judge only from practice and logical guesses.

And if possible, I have three more requests for you.
1) You cannot look at the 12 volt circuit that comes from the power supply to the main board; it’s okay that 12 volts will be supplied constantly during sleep or turning off the monitor through the button on the main panel. As I wrote above, 5 volts work constantly from the built-in power supply, but 12 volts are supplied only when the monitor is running. Just want to be sure that 12 volts will not damage the main board while sleeping or turning off the monitor.

2) In addition to power supply from the system unit, I want to implement LED backlighting with brightness adjustment using a variable resistance to avoid PWM diodes at low brightness (flickering). I understand that the diodes will heat up more, the efficiency will drop (energy consumption will increase slightly), but eye health is more important. I myself don’t know how to correctly calculate what power variable resistor should be placed in the circuit. According to the manufacturer, the energy consumption of the tape is 9.6 watts per meter. The tapes are cut at a distance of 5 cm, and my matrix needs two strips of 45 cm, that is, a total of 90 cm. And according to the manufacturer (which I don’t really trust), the consumption at 12 volts is 800 milliamps per meter of tape, minus 10% = 720 milliamps. But it is better to take a resistance with a good power reserve, at least 2-3 amperes. I would also like to add an additional ordinary resistance to the circuit, so that at maximum brightness (where the variable resistance supplies power directly), not 12 volts go to the diodes, but 10.5 - 11 volts, no more. This is necessary so that the diodes do not overheat at maximum brightness, and also to increase their service life, since completely disassembling the monitor and matrix box once again is a pleasure.

If it’s not difficult, then write the number or model (I don’t know how to correctly) of the variable resistance (you need to have a knob, like the volume of speaker systems, since there is a good place in the back of the monitor where it can be brought out) and how many ohms (even more likely kOhm) and Watt take a “simple” resistance, which will further reduce the voltage from 12 volts to 10-11 volts.

3) You also need to find a place in the power circuit of the main board, from where you can get 12 volts to power the LED backlight, where the power will be lost when you turn off the monitor from its power button and sleep mode. I myself can use a tester to find 12 volts, which disappear when the monitor is turned off and asleep, but I’m afraid that they suddenly pass through some kind of resistor or transistor, which can burn out from an additional load of 0.7-.08 amperes.

For several weeks now I have been assembling the most compact computer with standard components (that is, a standard power supply, standard motherboard, processor, RAM, even a laptop DVD drive). I brought out the missing "RESET" button and the missing indicators, replaced the terrible blue computer operation indicator with a warm orange one, installed a switch for the DVD drive (so that it would not make unnecessary noise when turning on the computer) and the amplifier and speakers, and also attached the amplifier itself to the face and volume control. All that remained was to wait for the arrival of dust filters on the case and power supply and a 6-pin connector to remove the speakers from the case and indicate their operation. I plan to screw the speakers to the bottom of the monitor case, and display the indication of their operation on the bottom of the case of the speakers themselves (the lower plexiglass of both will glow during operation). I was already glad that there was a little hemorrhoids left before the assembly of this Frankenstein was completed, and then they called me and said that the monitor had stopped working. It was a strong ambush :(
That’s why I want to do everything as reliably as possible, so that it works for a long time and doesn’t cause any more trouble for at least 10 years o_O.

P.S.
Sorry for the abundance of questions, I’m just afraid of unknowingly burning the main board of the monitor. Considering that this model has not been produced for more than 10 years (and as I already wrote, there are no alternatives to it, of the modern ones there are only two models on IPS matrices; they have been making them on VA for a long time, especially on PVA), but to buy the same used In good condition it is practically impossible (in Moscow and St. Petersburg they occasionally appear on sale). But if you buy it remotely, you will get darkening or scratches on the matrix, as well as broken or burnt-out pixels. When I bought the second 2190UXp through Avito, the seller from St. Petersburg assured me that the matrix was ideal, and when the monitor arrived, it turned out that the lamps had gone to zero (apparently that’s why I sold it, so that they wouldn’t completely fail) and as a bonus on top, I I received two dead pixels (fortunately, at least the pixels are not in the center of the screen and on the VA matrix they are not so noticeable, parents do not notice them at all).

What is known from the open spaces:




......

__________________________________________
ADDED 09/22/2012 07:44

Well, actually to the essence of the question. In short, the joke is that the client’s TV Samsung LE32R81 (8 lamps, 8 transfers, m/s OZ964) began to go out after 1 second as a standard. after switching on. Since no usual deviations in this case were found in the inverter, it was reasonably assumed that the problem was in the lamps. There are no lamps for mounting, which means you need to hang an equivalent...

Everything is known about Equivalents (although not without deviations, see above), but to be on the safe side, I decided to check this case against a similar existing one before moving it to the client. working Samsung LE32R75 (but the inverter in it is completely different, you can’t throw it in), weave it to guarantee. SO that’s where it all started - I tried to hang everything, instead of one of the lamps - both resistors 50-100-150-200 kOhm (at the highest you can smell a slight ozone smell), and conductors 47-68-120 pF. ... - fig. backlight after sec. after on just start blinking at a frequency per second, puff-peck-peck... i.e. the same as if with the lamp turned off.. What the hell is this, is there any theoretical explanation... for this matter?

In this material, the author continues the topic started in the article - he describes in detail the diagnostics of power inverters for cold cathode electroluminescent lamps (CCFL lamps). Circuit diagrams of all inverters discussed in the article are given in.

Correct fault diagnosis significantly reduces repair time and costs. The main problem that arises when diagnosing a backlight system is to determine what is faulty: the backlight lamp or the inverter. Practice shows that the malfunction of CCFL lamps manifests itself as follows:

The screen turns red;

When you turn on the laptop, the screen color has a red tint, and then gradually becomes normal;

The panel backlight (the entire image) blinks in time with the changing brightness of the scene;

The panel backlight begins to blink and then turns off.

The malfunction of the lamps with such manifestations is confirmed in approximately half of the cases; in other cases, it is necessary to refer to the methods outlined below.

Structurally, the inverter board and backlight lamps are usually located under the front cover of the laptop screen. The first thing to check is whether the backlight problems are related to a malfunction of the laptop motherboard. If, when connecting external display devices - a monitor, TV, projector, there is an image, then most likely the laptop's backlight system is faulty.

To repair an inverter or lighting system, you must have the minimum necessary measuring equipment at your workplace - a multimeter, an oscilloscope and an autonomous power supply with an adjustable constant voltage from 1.5 to 30 V with current protection (1 A), as well as a working CCFL lamp.

To eliminate the influence of a faulty lamp, an equivalent load is used when repairing the inverter. It is preferable to connect a known good lamp to the inverter being tested. If there is none, then a resistor with a nominal value of 100...130 kOhm and a power of 2...5 W is connected to the output connector of the inverter (as recommended by inverter manufacturers). The resistor is selected based on the required secondary voltage at the feedback output. A ceramic capacitor with a capacity of 20...200 pF and an operating voltage of at least 2 kV can also be used as an equivalent load. Using a capacitor when testing the inverter in operating mode is preferable, however, problems may arise when starting the inverter controller. The inverter can be considered operational if there is a stable sinusoidal voltage at the load equivalent.

Replacing a lamp requires special care and ensuring the cleanliness of the room. Work is carried out with gloves. In some cases, when complete disassembly of the matrix is ​​required, this operation is carried out in “clean” rooms and in special clothing.

Backlight malfunctions are sometimes associated with poor contact at the welding (soldering) site of the inverter wire and the lamp electrode. In this case, it is possible to restore the functionality of the backlight system. To do this, you need to have an insulating tube (rubber tip) from a faulty CCFL lamp. It is better to do welding or soldering with hard solder and a gas soldering iron, which creates a high temperature at the soldering site. The tube, previously placed on the wire, is carefully pulled onto the soldering site and the lamp is ready for use.

Malfunctions and repair of SAMSUNG laptop inverter

To access the inverter board and lamp, remove the decorative cover from the LCD panel of the laptop, disconnect the cable connecting it to the motherboard and the lamp connection cable from the inverter.

The screen does not light up

Check the serviceability of the inverter elements by external inspection. In this case, the malfunction of the power elements and, first of all, the transformer, is determined by the darkening of its body, burnt insulation, darkening and even destruction of the board underneath.

Check the presence of voltages on connector CN1 (Fig. 3c): +12 V on pins 1-2, inverter turn-off voltage on pin 4 and brightness voltage on pin 3.

In normal mode, when loading video card drivers, there should be no voltage on pin 4 of CN1. The inverter turns on automatically when supply voltage is applied. The brightness voltage (pin 3) must be at least 0.5...2 V.

Check the voltage at the emitter of transistor Q4, and if it is missing, check fuses F1, TF1, as well as transistors Q7 and Q5.

Check the serviceability of transistors Q1, Q2. These are digital transistors of the KST1623 type, they are produced in the L4 package, they can be replaced with an analogue of the BSS67R type. If transistor Q1 fails, it is enough to replace only it. If transistor Q2 fails, check the serviceability of transistor Q7 and operational amplifier U1A.

If fuse F1 is good and TF1 (self-resetting fuse) is faulty, then before replacing it, check the serviceability of transistor Q4 and zener diode D2.

Check the brightness control voltage on pin 3 of CN1. For diagnostics, pin 3 is supplied with a voltage of about 3 V from an external source. If the screen lights up, then the cause of the problem is the laptop's motherboard. In this case, you can forcibly turn on the screen backlight by applying voltage from a resistor divider (80 kOhm in the upper arm (to +5 V), and 40 kOhm in the lower arm) connected to the +5 V bus. If the screen does not light up, check the serviceability of transistor Q8 .

The backlight turns off 1-2 seconds after the operating system starts loading

First of all, check the serviceability of CCFL lamps. Connect the oscilloscope to pin 1 of connector CN2 (see Fig. 3c) and an equivalent load. If there is a sinusoidal voltage with an amplitude of 500...700 V and a frequency of 60...70 kHz at this ("hot") contact of the CN1 connector, then the inverter is operational and the backlight turning off may be due to a malfunction of the lamp or poor contact between the inverter wire and the electrode lamps. All this requires disassembling the laptop and removing the lamp. Observe the shape and voltage level at an equivalent load for at least 10 minutes, and replace the faulty lamp. If there is no voltage or its waveform is significantly distorted, then the malfunction is due to internal problems in the inverter.

Check the feedback circuit. If, when the inverter is turned on, an oscilloscope registers any signal at the “cold” contact of the lamp (its shape does not matter) with an amplitude of at least 1.5 V, and on the pin. 6 U1 voltage remains unchanged (constant voltage, which is measured with a multimeter), check the serviceability of diode assemblies D4, D5 (they can be replaced with any suitable ones, or with two separate diodes of the BAV99 type in SMD cases). If assemblies D4, D5 and resistor R14 (1 kOhm) are working, then the U1 chip is faulty.

Check the precision stabilizer U2 (TL341). If it is working, then on the pin. 5 U1 should be a constant voltage of 1.5V. In addition, this inverter protection line is connected with brightness control and overload protection circuit. To determine which of these circuits is faulty, turn them off sequentially (but not simultaneously) for a while. First, the protection circuit D3 R3 R4 is turned off, then the brightness control circuit - transistor Q8. If, when these circuits are disconnected, the lamps work stably, then the fault is in these circuits.

Check the presence of contact in connector CN2. In case of visible burning of the contact, it is restored. If the contact does not cause suspicion, connect an equivalent load. Check the overload protection signal generation circuit D3 C3 C4 D5. The protection may be triggered due to overheating of transformer T1, malfunction (leakage) of transistors Q5, Q6.

Malfunctions and repair of inverter based on MP1101 controller

The screen does not light up

Check for voltage on pins 4 (VCC), 2 (Enable) of connector JP1 (Fig. 4c). In this case, the supply voltage should be 12 V, the Enable inverter switching voltage should be at least 1.5 V. The absence of Enable voltage indicates a malfunction of the laptop motherboard, most likely the video card. The absence of 12 V voltage at the JP1 connector when the cable connecting the inverter to the motherboard is disconnected indicates a malfunction of the motherboard. If there is 12 V voltage at the connector, and at the pin. 6 U1 it is zero, then check the serviceability of the filter capacitors, fuse F1 and controller U1.

Check the inverter switch-on voltage at the pin. 4 U1. If it is missing, check its presence on the contact of the connector disconnected from the inverter board. If there is no voltage, check the laptop circuit. The absence of an inverter turn-on voltage can be associated either with a malfunction of U1 or with a break or “cold” soldering of the resistor REN1 (there are no designations of radio elements on the inverter board based on the MP1011 controller, so refer to Fig. 4 c). To eliminate this problem, simply solder the SMD resistor REN1. Check the serviceability of transformer T1 (see above), CON2 connector and wires.

The backlight turns on for 1-2 seconds and goes off

First of all, check the elements of the feedback circuit D2 (a, b) CSENSE RSENSE. Diodes are checked for open circuit or breakdown. Check the serviceability of the lamp (see above). Connect an equivalent load. Connect the oscilloscope to the Lamp+ circuit (Fig. 4c). If, after the operating system starts loading, a sinusoidal voltage of 500...700 V is present at this pin, then the main inverter board is working and the lamp needs to be replaced.

The reason for the backlight to disappear may be a malfunction of the feedback unit. If when you turn on the screen on the pin. 2, a positive voltage of about 0.5 V appears for a while, but the lamps go out, then the MP1011 controller should be replaced. If the feedback voltage is less than 0.1 V, check all elements in the feedback circuit: D2, RSENSE, CSENSE.

If, when the inverter is turned on, a signal with an amplitude of more than 0.5 V is recorded on the “cold” terminal of the lamp by an oscilloscope, and on the pin. 2 U1 voltage remains unchanged (constant voltage, which can be measured with a multimeter), then check the serviceability of the diode assembly D2, it can be replaced with two diodes of the BAV99 type. If the diodes are working and the RSENSE resistor (140 Ohm) is not broken (cold soldering), then the MP1011 controller is faulty.

Backlight turns off after a few seconds or minutes

In this case, check the T1 transformer, the CSER capacitor (for leakage) and the lamp connection wires for possible insulation damage and contact with metal objects of the housing.

Malfunctions of inverters based on the OZ9938 controller

The screen does not light up

Check the serviceability of fuse F1 (Fig. 5c). If it is faulty, then before replacing it, check the serviceability of transformer T1 by external signs (darkening, burnt insulation, burnt board). Then check the breakdown of the transistor assembly of field-effect transistors U1. If the OZ9938 controller is powered by a separate parametric stabilizer (not shown in the diagram), check the serviceability of its elements.

If the inverter circuit is working properly and there is a sinusoidal voltage of 550 V with a frequency of 55 kHz at pin 7 of transformer T1, then check the serviceability of the SG connector.

Check the presence of switching voltage (at least 1 V) on pin 6 of connector CN2. If the voltage is below normal, unsolder the pin. 10 controllers from the ENA bus. If the voltage at pin 6 increases to 2 V, check capacitor C18 or replace controller U2. If the voltage on pin 6 remains low, the reason is in the laptop motherboard. You can get out of this situation by applying a voltage of 2 V from an external source.

Check the voltage at the pin. 4 U2, if it is less than 0.1 V, then check the controller, laptop board and capacitor C10. Check the voltage at the pin. 11 U2, which in normal mode should be more than 3 V, with a reduced voltage at this pin, check C14, solder resistor R9. If the specified elements are in good condition, then replace the controller. The backlight turns on for 1-2 seconds and goes off

This defect may be due to a malfunction of the lamp and its connection circuit. If the lamp is working, then check the feedback circuit D1 C22. If, in the absence of a signal to turn on the inverter, the voltage at pin 6 of U2 is more than 1 V, then this microcircuit is faulty and must be replaced. If the voltage at the pin. 6 less than 0.7 V, the lamp is working, and the backlight turns off within a few seconds, check the overload protection circuit D2 R5 R3. If the voltage at the pin. 6 when the inverter is turned on, increases and at one moment exceeds the voltage of 3 V and at the same time the lamps turn off, then the reason is the overload of the inverter output stage. This may be caused by a faulty lamp (start-up problems when the lamp takes a long time to start-up). In addition, overload may be due primarily to the presence of short-circuited turns of the transformer windings.

If the voltage at the pin. 6 does not exceed 3 V, but the lamp turns off, then check for a voltage of no more than 3 V on the pin. 7 U2. If the voltage is below this level, then check capacitor C8 (leakage) or replace controller U2.

The backlight turns off a few minutes after turning it on

Check the overload protection circuits D2 C2 C5. Check the serviceability of transformer T1 (see above). Sometimes the malfunction appears after some time, during which the transformer heats up (above 50°C), then it is necessary to replace it. Check the serviceability of the transistor assembly U1 (can be determined by its operating temperature). As a rule, this malfunction disappears while the suspicious elements are “frozen” with Freeze gel. If the time after which the backlight turns off is unstable, then check the serviceability of the lamp and its connector.

Malfunctions of inverters based on the OZ960 controller

The screen does not light up

For inverters such as AMBIT and KUBNKM (see Fig. 6 c), this may be accompanied by a lack of indication on the front panel. In this case, disassemble the laptop and check for +12 V voltage (for KUBNKM inverters the input connector J1 (CN1) is 20-pin, the supply voltage is supplied to the 4 outermost pins, and for AMBIT inverters the connector is 16-pin, and the supply voltage is supplied to the 2 outermost pins contact). If fuse F1 is faulty, check transistor assemblies U1, U3. Check the presence of supply voltage at the pin. 5 OZ960 controllers (U2). This voltage, in contrast to a typical inverter circuit (Fig. 6c), comes from pin 1 of J1 through the stabilizer on transistor Q1 (designation on the board). In AMBIT inverters, controller U2 is powered from pin 4 of J1. There may be no supply voltage at the connector itself due to a faulty laptop power supply or due to a short circuit to ground at the pin. 5 U2. For diagnostics, disconnect the SVDC line from connector J1 and, if voltage appears on the bus, then the inverter is faulty.

Check the presence of the ENA controller turn-on voltage on the pin. 3 U2, it must be at least 2 V. In the KUBNKM inverter, the controller turn-on voltage comes from transistor Q1 (its supply voltage is also removed from it) but through a 10 kOhm resistor. Other modifications of inverters based on the OZ960 controller may also have their own characteristics and differences from the standard circuit, but the troubleshooting technique for them is the same.

If the LEDs on the laptop keyboard panel are lit, there is no screen backlight, and the voltages listed above are present, then check the serviceability of field-effect transistor assemblies U1, U3, as well as zener diodes D1, D2 (4.7 V).

When you turn on the laptop, use an oscilloscope to monitor the presence of rectangular pulses on the pin. 11-12 and 19-20 U2. If there are no pulses and the U1, U3 assemblies are working properly, then check for the presence of a voltage of 2.5 V on the pin. 7 U2. If it is missing or it is underestimated, check C13 and replace the controller. Check for the presence of a sinusoidal signal at the pin. 18 U2 with a frequency of 50.60 kHz. If the frequency differs significantly from the nominal one or there is no signal at all, check elements C5, R4.

The lack of backlight may be due to the lack of (low) voltage at the pin. 14 controllers. If the voltage at this pin is less than 1 V, apply a voltage of 3 V from an external source. If the screen lights up, then the problem is related to the brightness control voltage supplied from the laptop board. In this case, you can apply voltage from pin 1 of J1 to the brightness control input through a resistive divider, but it must be taken into account that the brightness will not be adjusted

The backlight turns off 1-2 seconds after turning on the laptop

Make sure that the backlight lamp is working properly (see the verification method above). They are connected with an oscilloscope to the “hot” (upper in the diagram in Fig. 6c) output of transformer T1. If, when you turn on the laptop, a sinusoidal voltage with a frequency of 55...60 kHz appears at this pin and immediately disappears, check the serviceability of transformer T1. Then they check the serviceability of the transistor assemblies U1, U2 for leakage: measure the resistance between source and drain with an ohmmeter, and if it shows the final value at the limit of 100 kOhm, then replace the assembly. Check the serviceability of capacitor C4 for leakage (ESR).

Check the presence of feedback voltage at the pin. 8 of the controller, it must exceed 1.25 V. If the voltage is below this value, check the diode assembly CR1, and also solder resistor R8. If there is no result, replace the U2 controller.

Backlight turns off after a few seconds or minutes

In this case, check the surge protection circuit. Disconnect it from the main circuit (just unsolder the CR2 diode assembly). When you turn on the laptop, check for voltage at the pin. 2 controllers (should be no more than 1 V). If this voltage exceeds the specified level, check the threshold value of 2.5 V at the pin. 7. If it is missing or the voltage is too low, replace the controller. If the voltage at the pin. 2 is normal, but when the protection circuit is connected, the voltage becomes higher than 2 V or changes over time, check the serviceability of the transformer, capacitors C7, C11, diode assembly CR2. You can replace the transformer with any type from another inverter (this circuit is insensitive to the type of transformer), the only thing that will need to be adjusted is the feedback voltage coming from the cold end of the lamp (by selecting resistor R8).

In an AMBIT type inverter, which uses an OZ979 chip to power the keyboard LEDs, you can try to restore the screen backlight using a temporary scheme. The lamps are turned off and lines of LEDs are fixed (glued) on the back side of the LCD matrix at the top and bottom of the screen, 3 pieces each. in 5 lines, the first LED is connected to pin 3 of the OZ979, and the last one is connected to the housing. This method is suitable for small screens of 10-12 inches.

You can use an inverter circuit based on OZ960; after the transformer, instead of capacitor C4, a double diode in an SMD package and a quenching resistor with a nominal value of 50 Ohms are installed. The resistance is more accurately selected when installing LEDs to ensure normal illumination and, depending on their operating current, for normal illumination of a 15-inch display, 16 ultra-bright LEDs, for example FYLS-1206W white, are sufficient. LEDs can be glued to fluoroplastic tape and connected with thin conductors. In this case, the input voltage on the first LED should not exceed 80 V at a current of 25-50 mA. The current through the LEDs is set by selecting the value of the limiting resistor.

Some circuits based on OZ960 differ from the standard one, including the name and location of some electronic components.

Sometimes there is a decrease in the brightness of the backlight and its adjustment is not enough. This occurs due to a decrease in the current of the gas-discharge lamp due to an increase in the transition resistance at the contact point on the board of the high-voltage winding of the transformer T1 and the ballast capacitor C4. The problem is eliminated by soldering the capacitor leads.

Literature

1. Vladimir Petrov. Repair and maintenance of power inverters for backlight lamps of LCD panels of laptops. Repair & Service, 2010, No. 3, p. 37-40.

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 conversion is not so difficult, and there are no special problems 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 have 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 an external power source.

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 in this case it 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 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 any N-channel field-effect transistor (field transistor). 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.

• Any equipment has its own service life. LCD monitors are no exception either. A very common problem with them is the failure of the screen backlight lamps. In this case, you should not rush to write him off. You can repair your monitor by replacing the matrix backlight lamp. When searching for the required parts, it is not always possible to find the required CCFL (fluorescent) lamps. Replacing your old LCD monitor backlight with LED is not difficult. There are plenty of necessary spare parts on sale; you can use a strip of LEDs.

  Replacing the monitor backlight with LED

  Backlight repairs should be carried out following certain rules and the sequence of work. First you need to make sure whether the backlight of the monitor matrix has really failed, because not only it can be responsible for the supply of light. Most often, such a breakdown is manifested by a blackout monitor, which can be not only a computer monitor, but also a TV monitor. It may also turn on and then go off after a few seconds. To identify this problem, you will need to disassemble the monitor.

  Disassembling a PC or TV monitor

  It is not that difficult to describe the process in detail, but each model and brand has its own characteristics, sizes and is assembled differently. However, the assembly principle is approximately the same. You can briefly describe the disassembly of the monitor.

  It is necessary to remove the stand by unscrewing the screws that hold it, as well as the remaining fastening elements of the case.

  At the end of the device there is a special groove, which is designed to open the latches by prying the cover with a flat object. When disassembling the monitor for the first time, you will notice that the latches fit tightly, but the next time you open it, the process will be easier.

  Now you need to remove the metal frame. To do this, you need to bend the latches or unscrew the screws from the case. For those who have already changed any parts on similar equipment, this procedure will not seem difficult. After removing the metal case, disconnect the wires from the board.

  Once these steps are completed, the matrix will become available. It has connecting cables, due to the fragility of which you need to be extremely careful with it. It is advisable to remove the matrix to the side and cover it with something to prevent accidental damage and accumulation of dust. If the work is done correctly, you can easily reach the inverter, electronic board and lamps. If you decide to redo the backlight for your monitor, you should remember the location of all the parts to be removed, although it will be difficult to confuse them.

  
  

  Next, you need to disconnect each lamp directly from the matrix. When the grooves are dismantled, the backlight sources can be removed from there and simply thrown away. Anyone who has not yet converted their monitor backlight from CCFL to LED should know that due to the presence of mercury in CCFL lamps, you need to be extremely careful when working with them. The next step is to replace the monitor backlight using LED strip.

  DIY monitor backlight

  To begin with, before replacing the backlight bulbs, you need to purchase a strip with LEDs. It’s better to buy it with the dimensions already taken from the lamps or take a tape a little longer. There should be at least 120 LEDs per meter, and it is better to choose a color that does not put pressure on the eyes.

  LEDs that illuminate the monitor in white are ideal. You can choose a tape with crystals 3528 and 4115. Its size must correspond to the mounting location where the LED backlight of a PC or TV monitor will be mounted. Typically the standard size is 7mm. A kit for replacing CCFL monitor backlight lamps with LEDs may come with a different number of LEDs, but their performance and service life are much higher than those of older light sources.

  
  

  removed lamps, in their groove. You can use old wires from removed lamps to further connect them to the power source. In such situations, it is better to check whether the LED backlight circuit is assembled correctly. To do this, you can connect it using wires to an external power source, for example, a battery.

  The next step is to connect the new backlight to the power board installed on both PC and TV displays. To ensure that the modification does not fail, you should pay close attention to this point. Anyone who has connected low-current devices to a network with a voltage higher than necessary knows that the device will burn out. This will happen due to the fact that the resistance of the device is designed for smaller values. So, you will need to find the 12 V pins on the board and solder the wires from the new LED backlight to them, while maintaining their polarity. Now you can start assembling your TV or PC display.

  Do-it-yourself LED backlighting in the monitor has one significant drawback. Since the connection is made directly, there is no adjustment or disconnection. Therefore, it is constantly on when the monitor is on. Such a bright glow will dazzle and annoy the person looking at the screen.

  
  

  To create a backlight control, you need to re-energize the wires connected to the strips, with the ability to turn it on and off using certain buttons. There are 2 ways to accomplish this task:

  1. You will need to assemble a circuit that will be used to adjust the power and intensity of the backlight. To do this you need:
  • Find the plastic connector located on the power supply board of the monitor or TV display. It is not difficult to recognize it - wires will come out of it with a socket labeled for each of them.
  • To ensure switching on and off, you need to use the “DIM” sockets. Brightness adjustment occurs by changing the wellness in the PWM controller.
  • Now you need to find a field-effect transistor with channel N. After this, solder the negative wires from the LED strip to the terminal (Drain) of the field switch. The common wire from the LEDs is connected to the input element (Source). The circuit provides for the use of a resistor with a value of 100 to 2,000 Ohms, through which the Gate of the transistor is connected to any “DIM” socket.
  • All that remains is to solder the positive wires from the LED backlight. To do this, you should connect them to a 12 V power chip, and then solder them.
  • After completing all of the above steps, you can install the backlight in the mounting locations and begin assembling the monitor in reverse order. It is worth remembering to be careful with the matrix and filters. After assembly, the device is ready for use.
  
  
  1. The second method is to use LED strips with inverters built into them:
  • To connect the circuit with this method, you will again need a plastic connector with a DIM socket, as well as an on/of pin. It is better to determine this socket by pinout.
  • When using a multimeter, the sockets on the control unit, which was responsible for the monitor backlights, are called up. The signal must pass from them to the DIM and on/of sockets.
  • The next step is to solder the wires of the LED strip inverters to the found sockets. To adjust the backlight using an inverter from LEDs, you will need to remove the wires that power the old lamps.
  • You can secure it wherever there is free space using double-sided tape.
  • To complete the modification, all that remains is to assemble the monitor and test the new backlight in practice.

  Converting the monitor backlight from lamp to LED in this way ensures its longer performance and efficiency, which, of course, will please every user.