Typical fault repair summary of LCD logic board - android - Phones Developers

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Typical failures of logic boards are:
No image, there are intermittent color lines in the vertical direction of the screen, and no characters (this is very important).
You can test the screen voltage, depending on the 5V or 12V screen model.
Then test the voltage on the LVDS output interface to see if the static and dynamic conditions change. If there is no change, you can judge the fault on the logic board. (When measuring, use the pointer multimeter. You can see that the hands have slight jitter, generally 1.2V or so), if you have the conditions, take the same logic board for the most reliable replacement, as long as the format and the screen voltage can be replaced, so that we can find the fault point.
The LVDS line from the main board to the logic board has a certain regularity. The red side is the positive pole of the power supply, the black line is generally the negative pole of the power supply, and the LVDS signal line is twisted together:
(4 pairs - single 6 digits; 5 pairs - single 8 digits; 8 pairs - double 6 digits; 10 pairs - double 8 digits),
Now some logic boards and screens are connected together, called X+C integrated type, generally 32-inch screen, 32-inch screen is generally composed of X+C separate type (small screen is mainly considered by cost) Due to the technical and precision characteristics, it is generally not easy to repair. If the principle is thoroughly penetrated and the welding technology is excellent, the maintenance logic board is not a myth!
Damage to the logic board can cause the screen to not display the image properly, and of course there is no menu display, but the buttons and remote control are functional (remember this).
The intermediate image of the screen with poor contact between the logic board and the screen connection line is mixed with many small color points, which can be inserted and removed to confirm;
Both the logic board and the screen can cause the image to be screened, but the screen of the logic board is different from the screen produced by the screen. The screen of the logic board is a regular flower screen. We can change the signal source or change the 4:3 mode to confirm. .

Logic board maintenance summary (overhaul ideas)

1. Appearance check to see if the main chip power supply IC filter capacitor or other vulnerable components are obviously burnt black or color abnormalities;

2. Measure the resistance of each power supply test point to see if there is a short circuit resistance value, and whether the insurance has an open circuit;

3. Measure the voltage to check whether the power supply measurement points are normal (1 power supply Vcc5V/12V, 2 main chip 3.3V; 2.5V; 1.8V, 1.2V, etc., 3VAA14V, VGH20V, VGL-5.5V, 4VREF13V, VCOM 6V) ;

4. Measure whether the data exchange between the IC signal line and the ground resistance LVDS DDR and the main chip is bad;

5. Check whether there is any contact failure between the plug-in line and the logic board and between the logic board and the screen.

In fact, the LCD TV logic board, in addition to the LCD screen LVDS program failure, other faults are still good repair.
Therefore, according to the requirements of netizens, I removed the cumbersome content and used the easy-to-understand language to repair the LCD TV logic board, first published in China Appliance Repair Network.
The following is the maintenance idea of ​​the LCD TV logic board (1) recognize the logic board and LVDS signal: (2) how to quickly determine the fault on the LCD TV logic board circuit.
The logic board is provided by the screen manufacturer and the screen. The logic board is also called: screen driver board, center control board, TCON board. The function of the logic board is to input the LVDS input signal from the digital board. (The input signal contains three categories: RGB data signal, clock signal and control signal.) After processing by the logic board, the LVDS signal inputs the TTL level in parallel. After the RGB data signal is converted into an LVDS signal capable of driving the liquid crystal panel, it is directly sent to the LVDS receiving chip on the side of the liquid crystal panel to drive the liquid crystal screen to display an image.
The faults caused by the damage of the logic board are: black screen, white screen, gray screen, negative image, noise point, vertical band, image is too bright or too dark.
What is the LVDS output interface? LVDS is a low voltage differential signaling technology interface. A digital video signal transmission method developed to overcome the disadvantages of large power consumption and large EMI electromagnetic interference when transmitting broadband high bit rate data in a TTL level manner.

The LVDS output interface utilizes a very low voltage swing to differentially transmit data on two PCB traces or a pair of balanced cables, ie low voltage differential signaling. The LVDS output interface allows signals to be transmitted over a differential PCB line or balanced cable at a rate of a few hundred Mbit/s. Low voltage and low current drive are used to achieve low noise and low power consumption. Pay attention to the maintenance: If you only look at the circuit diagram, you can't see the signal data contained in the internal output signals TXOUT- and TXOUT0+ of the LVDS transmission chip, and how the data is arranged. Because the LVDS transmitting chips produced by different manufacturers, the output data arrangement may be different. Therefore, the output data format of the LVDS transmitting chip on the LCD TV logic board must be the same as the data format required by the liquid crystal panel LVDS receiving chip. Otherwise, the logic board does not match the liquid crystal panel. This is also a problem that must be considered when pointing out the screen. This is also an important piece of information for the dot screen.
(2) How to quickly judge whether the LCD TV logic board circuit is faulty Whether the LCD TV logic board circuit is faulty, it must be detected by detecting various related signals, and the fault can only be confirmed by analyzing according to the detection result. The following is a quick way to determine the fault of the LCD TV logic board circuit:
(1) Whether the waveform of the input video signal sent by the digital image processing circuit is normal on the detection logic board. If there is a normal waveform input, the previous digital image processing circuit works normally.
(2) Check whether the voltage input from the power supply on the logic board is normal. If the input voltage is normal, the power supply circuit works normally.
(3) Check whether the waveform of the LCD screen drive signal outputted by the screen line interface on the logic board is normal. If there is no normal waveform output of the LCD screen drive signal, there may be a fault in the logic board circuit.