How to check the backlight lamps of an LCD TV

These days, a modern LCD TV can be found in almost any home. It is a source of information and entertainment, so it is very annoying when the TV breaks down. Most often, in such equipment with a liquid crystal display, the matrix backlight breaks down, but this malfunction can be easily fixed if you know the basic principles of diagnostics and repair.

How to check the LED backlight of a TV?

A malfunction of the LED backlight of the TV matrix has a number of signs that you should definitely pay attention to before starting the analysis:

• When you press the corresponding button on the remote control or front panel, the TV turns on, there is sound, but there is no picture.
• When the TV is turned on, it responds to pressing the remote control buttons, switches channels, turns up the volume, but the screen remains dark.
• If you look closely at the screen matrix, you can see a very dim image on it.

The presence of such factors allows us to talk about the failure of one of the line of LEDs or the backlight control driver. In any case, the TV will need to be disassembled to eliminate the defect and restore functionality.

Disassembling the device: nuances and features

The range of modern LCD TVs is incredibly extensive, but in most cases their design is quite standard, and they are disassembled according to the same principle. The disassembly procedure occurs in several stages:

• Preparation of the workplace. You should first take a set of tools, several tables for laying the matrix and scattering films, a soldering iron, antistatic gloves and napkins.
• Removing the back cover. As carefully as possible, the TV should be placed as a matrix on the table, the stand should be removed, and all the bolts holding the cover should be unscrewed.
• Removing the T-con board. Easily removed after disconnecting the cables and unscrewing the bolt.
• Removing the metal protection and unscrewing the decoder block.
• Removing the front frame of the TV by unscrewing the mounting bolts around the perimeter of the device.
• Removing decoders from rubber mounts.

ATTENTION. Decryptors are very fragile and critical devices, so they should be removed with extreme caution!

• The matrix remains on the table and you can proceed directly to finding and replacing faulty LEDs or the controller in the backlight system.

LED backlight fault detection

The reason for the lack of backlight on the LCD TV display may be a failure of the driver or the LEDs themselves. You can determine which device is broken in the following ways:

• If the driver fails, there is no voltage on the diodes - this can be checked by connecting a multimeter.
• If the LED strip is faulty, then a voltage of 150-200V will be supplied to the power terminal. You can also check each of the diodes with a multimeter.

Replacing LEDs in the backlight

Having identified faulty LED lights in the matrix backlight, you should replace them with new ones. They are dismantled quite simply - you need to peel off the strip from the body using a hair dryer, and also remove the lenses. Next, you can start desoldering the LED itself and soldering in a new one. Be sure to thoroughly wipe the diode from flux and carbon deposits, otherwise the image on the TV display may be distorted.

If several LED elements on the backlight diode strip burn out at once, you can replace the strip with a new one. The procedure is also performed by soldering, but takes much less time.

Final stage

After soldering new diodes instead of the burned ones, you should assemble the driver and check how the backlight works. If everything is fine and the LEDs do not start to go out or blink within a few minutes, you can start assembling the TV.

Particular attention should be paid to connecting all buses and cables, doing this as carefully as possible, trying not to damage the connectors. When the assembly is completed, with the matrix and all blocks already installed, you should turn the TV on and off several times, thereby putting an intense load on the driver and the LED elements themselves.