Introduction to T-CON and maintenance matters

T-CON board is also called logic board or control board. T-CON is the English abbreviation of Timming Controller, which means timing control circuit. At present, there are not many T-CON boards in China, CRT TV has a history of several decades. The traditional CRT TV works by scanning, and the signals are serial. The current TV standard is based on CRT TV, so the TV signal passes through the TV main board. The output after decoding is also a serial signal. We know that the liquid crystal display works in a matrix display mode, and it processes parallel signals. That is to say, if the TV signal decoded by the motherboard is sent directly to the LCD display, the LCD display is Can't be displayed. There must be a device that converts serial signals into parallel signals so that the LCD can display TV signals, so there is a T-CON board, which is a device that converts serial signals into parallel signals. The TV signal output by the main board is disassembled and recombined in the T-CON board to finally form the control signal and data signal required for the row and column drive of the liquid crystal display. The general T-CON board circuit can be roughly divided into three parts: signal processing circuit (main IC and its peripheral circuits), gray-scale forming circuit (GMA forming circuit), and power supply circuit (DC/DC circuit). The signal processing circuit mainly converts the TV signal transmitted from the motherboard into the control signal, pixel signal, auxiliary signal, etc. required for the LCD display; the gray-scale forming circuit mainly forms the gray-scale signal required for the LCD display (the grayscale can make The display of the LCD screen is more layered, making the display richer and more vivid). The power supply circuit mainly forms the signal processing IC, the power supply voltage of the row drive and the column drive, and the switching voltage of the TFT (TFT turn-on voltage VGH, TFT turn-off voltage VGL) and so on.

Common faults and analysis of T-CON board:

1. The color of the display screen is abnormal

Generally speaking, the abnormal color of the LCD screen has a lot to do with the signal processing IC. The internal structure of the signal processing is complicated and the integration is high, and it is easy to be damaged by static electricity, sudden strong voltage and high current. Most of the picture abnormalities are caused by the damage of the signal processing IC. The IC outputs the control signals and pixel signals needed for the LCD display. After the IC is damaged, the control signals cannot complete the orderly arrangement of the pixel signals, so the picture is abnormal. In addition, damage to the FFC (flexible cable) or improper connection will also cause screen abnormalities.

2. There is no picture on the display screen

There is no image on the display screen, which means that the IC has no control signal and pixel signal output. There are several reasons that cause the display to have no picture: 1. The IC is seriously damaged, resulting in no control signal and pixel signal output, and the display is not available for display. The image input is not displayed; 2. The IC does not work due to the damage of the voltage regulator chip to the IC, so there is no image; 3. The failure of the power supply circuit (DC/DC circuit) causes the voltage required for the operation of the IC cannot be provided, so there is no image .

3. The grayscale picture in the display screen is abnormal

The abnormal gray scale picture has a lot to do with the GMA forming circuit. The GMA voltage is formed by a series of VS voltage signals collected by the resistor divider array after being amplified by the integrated operational amplifier and then outputting a series of GMA voltage signals. In the process, the GMA voltage signal is used as the reference standard, and the abnormal GMA voltage will cause the grayscale picture to be abnormal.

Repair method of control panel

1. No diagrams and circuit diagrams with power supply parts caused by faults in the power supply circuit of the control board:

The power supply part mainly provides working voltage for signal processing IC, row drive circuit, and column drive circuit. Except for GMA voltage, almost all voltages are generated by this circuit. Failure of the power supply part will inevitably cause other circuits to fail to work due to abnormal power supply, resulting in no picture on the LCD screen. When overhauling, first measure whether the fuse is burnt out, and when it is found that the fuse is burned out, replace the fuse and re-energize to check the screen. There is no problem with the fuse. First, use a multimeter to measure whether the VON (VGH) voltage is about 31.5V and the VOFF (VGL) voltage is about -5V. If the VON and VOFF voltages are abnormal, measure whether VD10 has a breakdown. If there is no breakdown, the BD8161EFV chip may be damaged. If VON and VOFF are normal, measure whether the LVDS interface is 12V. If the 12V voltage cannot be measured, it is likely that the control board circuit has a short circuit. If 12V is normal, then measure whether VDD is 3.1V. If it is not 3.1V, it proves that the output of BD8161EFV chip is abnormal. If VDD is 3.1V, it is probably not caused by the power supply circuit. If there is a short circuit around the BD8161EFV chip, first use a hot air gun to blow the chip down, and use a multimeter to measure the disappearance of the short circuit. It is proved that the short circuit is caused by the chip, and the chip can be replaced. If using a multimeter to measure that the short circuit still exists, you need to eliminate the short-circuited components one by one.

2. Picture abnormality caused by signal processing IC failure:

Most picture abnormalities are caused by signal processing IC failures. The T-CON chip (signal processing IC) generates control signals to control the orderly arrangement of pixel data on the row electrodes and column electrodes. When the signal processing IC fails, the normal control signal cannot be generated to arrange the pixel data in an orderly manner, resulting in an abnormal picture; the signal processing IC failure will also cause the LVDS signal sent to the T-CON chip to fail to be converted into an RSDS control signal , Resulting in a white or black screen on the display screen. The picture abnormalities caused by the signal processing IC include all the display pictures are disorderly, TN models only display black pictures, and MAV models only display white pictures, blurry screens and so on. An oscilloscope is needed in the repair process to determine the IC failure. First use an oscilloscope to measure whether the waveform, amplitude, and duty cycle of the STH signal are normal. If it is not normal, it can be judged that the signal processing IC has a problem. Replace the IC, and the general fault can be eliminated. If the STH signal is normal, then measure the waveform, amplitude, and duty cycle of STV, OE, CKH, STB, CPV, CKV, POL and other signals respectively. Until it is determined that the signal processing IC is malfunctioning. After the repair time is long, according to which screen is abnormal, it can be deduced whether it is the fault of the signal processing IC.

The role of each signal generated by the signal processing IC is attached.

1. The start signal of the driver IC.

2. The POL reversal signal determines the reversal mode.

3. The STB gate input allows the signals of the same horizontal line to enter at the same time.

4. The CPV/CKV row drives the IC clock. The CKH column drives the clock of the IC.

5. STH column

6. The start signal of STV row driver IC.

7. OE prevents the same signal from being transmitted to two adjacent horizontal lines at the same time.

3. Repair of abnormal gray scale picture: Circuit diagram of gamma voltage forming circuit:

If the LCD screen has a sense of hierarchy, it is necessary to add grayscale when displaying. The grayscale is formed in the column driver IC, and the GMA voltage is used as a reference during the grayscale formation. When the GMA voltage is abnormal, the screen will be abnormal in the grayscale screen. When repairing, measure the GMA voltage test points to see if there is a short circuit between the GMA voltage test points. When a short circuit is found, first suspect that there is a short circuit inside the integrated operational amplifier. Replace the integrated operational amplifier and re-measure each GMA voltage test point. If the voltage is normal, it proves to be the problem of the integrated op amp. If it is still abnormal, analyze the components between the two GMA voltage test points to find out the component that caused the short circuit. Replace the circuit and it will return to normal. Measure the GMA voltage test point but no short circuit is found, then measure the GMA voltage value at each point to see if it is normal, find out the point where the GMA voltage value is abnormal, and measure the voltage drop to each component of the integrated operational amplifier to find out the voltage Replace the abnormal component to see if the voltage at the GMA voltage test point returns to normal. If it is not normal, it is likely that there is a problem with the integrated op amp.