The nature of the malfunction and the possible cause
If the inverter breaks down:
- you cannot make out what is happening on the screen, the picture is dark and blurry;
- the image appears for a long time, is distorted and flickers;
- after turning on the TV, the monitor goes out almost instantly.
The power supply is out of order:
- the picture has lost its brightness and twitches;
- Forms are not being submitted correctly
- the image is lagging.
The problem is in the matrix loop:
- ripples and interference;
- repetition of images and stripes;
- signal disappears periodically.
The backlight of the liquid crystal polymer layer is faulty:
- flashing image;
- dark display with indistinguishable or dull silhouettes;
- the problem occurs on half of the screen.
How to conduct a general TV diagnosis
First of all, you need to enter the TV receiver’s menu, add brightness, check the contrast settings. It is necessary to make sure that the display parameters are set correctly, in accordance with the device operating instructions. Next, you need to disable energy saving, if enabled. Also exit night mode if your device supports it.
In addition, before checking the TV itself, you need to make sure that the external connections are secure. If possible, replace the HDMI cable. Check that the TV signal source. digital set-top box of terrestrial television, satellite TV. is functioning properly.
If there are several TV receivers in the house, you can check the operation of all peripherals by replacing the TV with a known good one. If everything is in order, you need to diagnose the device itself. To do this, it is advisable to have some skills in radio electronics or entrust the work to the master.
Darkened TV screen: what to do
If the TV screen darkens, the brightness disappears, the picture becomes dim or disappeared completely, first of all, you should study the instructions and check the device settings. In the event that the TV receiver is adjusted correctly, and the picture is missing or poor, you will have to look for a malfunction.
How to replace LED backlight bulbs
A burnt out diode or lamp can be detected by illuminating a darkened, dimmed part of the TV screen with a flashlight. In the case when the image has become more visible, most likely, the backlight elements of the LCD matrix are faulty.
Disassembly of the TV receiver
To remove the back cover, unscrew the mounting bolts after placing the device with the matrix down on the table. After that, you need to act like this.
- Disconnect the T-con circuit cables and remove the board.
- Unscrew the metal protection of the decoder and remove it.
- Unscrew the front frame bolts along the edges of the housing and remove it.
- Disconnect and remove the decoder. The matrix must be carefully held by turning the screen over.
- Loosen the latches and remove the diffusion film.
- Remove retaining clips, remove reflector.
Having gained access to the backlight elements, they begin to check it.
Replacing the backlight lamps
Some breakdowns are easy to identify by the appearance of the failed parts. The presence of deposits, transformations of the color of the lenses or burning indicates a malfunction of the damaged elements.
Lamps are located along the entire perimeter of the screen in horizontal rows or at the top and bottom of the monitor in pairs in pencil cases. It is often possible to determine the faulty element by the characteristic darkening of the cathode. If this fails, you will have to check each method of replacement for a known good.
If, after eliminating the identified problems, the backlight does not work as it should, or there are no external breakdowns, then check the diode rulers and parts separately.
For this you need:
- power up all the LED strips in turn, controlling their glow;
- if the semiconductor line does not light up, you will have to find the failed elements by examining each diode;
- replace the inoperative part with a soldering hair dryer;
- in case of a critical number of burnt parts, a new tape should be glued.
After checking the functioning of the backlight, the device is assembled.
If the LED diagnostics reveal no problems, the power driver is examined. In this case, power is not supplied to the tape or is in an unacceptable range.
You will need knowledge in the field of circuitry to check the values of the currents and analyze the operation of the power supply.
Possible causes of the problem
On modern TV models, such as LG or Samsung, the TV screen often goes dark if:
- energy savings are displayed;
- night mode is always on;
- the brightness or contrast is incorrectly adjusted;
- the LEDs or backlight lamps of the screen are out of order;
- the operation of the backlight control circuit is broken;
- the inverter driver is faulty (a characteristic darkening of the middle of the monitor appears);
- the converter module burned out;
So, if only the lower part of the screen of older models (with a thicker body) darkened, most likely there is a problem with one backlight lamp or its power supply circuit. In newer versions of TV receivers, dimming can be caused by the breakage of the LED strips, which illuminate the liquid crystal matrix from the inside. The elements of the tape are connected in series, and when one of them burns out, then the entire tape turns off.
During normal operation, the backlight is supplied with a supply voltage from the inverter (about 200 V). This provides a backlight control LED driver. A disruption in its functioning may also be due to the fact that the TV began to show darker.
The dark screen may not be related to settings or backlighting. The reasons that there is sound, but there is no picture, may be the following factors:
- defective HDMI cable;
- the elements in the power supply are out of order, for example, capacitors;
- the work of the mother (main) board is broken;
- the matrix itself suffered;
- problems with the input signal (antenna, TV set-top boxes, cables, connectors);
- breakdown in a decoder, loops or converter.
To accurately determine the malfunction, it is necessary to carry out a complete diagnosis of the device.
Darkening of the TV screen occurs in most cases due to a malfunction of the LCD backlight circuit. You can replace defective lamps or LEDs yourself. First, you should make sure of the cause of the problem by illuminating the display with a bright flashlight. If the lighting devices themselves in the device are in good working order, it is better to carry out further electronics repairs in a specialized service center.
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