Which part of the LCD TV is faulty will cause the TV to malfunction? In the LCD TV, only the frequency conversion processing circuit in the signal processing circuit does not work properly, and the screen failure occurs. Therefore, when troubleshooting the "flower screen" fault, the inspection focuses on the frequency conversion processing circuit in the signal processing circuit. Guangzhou Bolei Electronic Technology Co., Ltd. , https://www.nzpal.com
The circuit structure in the LCD TV is different, the chip used is different, and the structure of the frequency conversion processing circuit is also different. The inverter processing circuit in the LCD TV has three circuit configurations: the first consists of two independent integrated blocks, the second consists of a non-independent single integrated block, and the third consists of independent integrated blocks + non-independent integration. Block composition.
The figure below is a physical diagram of a typical representative circuit of a variable frequency processing circuit composed of two independent integrated blocks, which is a frequency conversion processing circuit in the signal processing circuit of Changhong LS10 movement. The inverter processing circuit in the figure below mainly consists of the integrated blocks MST5151A and K4D2632381. In the figure below, the MST5151A, which has a lot of upper pins, is a dedicated block for inverter control. The integrated block K4D2632381 with fewer pins is a frame memory. The relationship between the two integrated blocks is that the frame memory operates under the control of the variable frequency control circuit. As you can see from the figure below, there are many connections between two integrated blocks. These connections are usually called clock lines, data lines, and address lines.
The integrated blocks in the LCD TV signal processing circuit are typically mounted on one side of the board. The layout of the clock lines, data lines, and address lines on the board in the inverter processing circuit may vary depending on the board structure. Some are connected by one side of the circuit board, and some are connected from one side of the board to the other side through the via hole, and after a certain distance on the other side, then go through the via hole to the side with the integrated block The relevant pins are connected. Cross-hole communication is also one of the conditions to ensure the normal operation of two ICs.
In the picture, the digital video signal from the AD conversion circuit and the VGA signal from the VGA signal input interface directly enter the variable frequency control integrated block MST5151A, and then the frequency conversion processing is completed by the combination of the frequency conversion controller and the frame memory, and the signals of different formats are changed. A unified LVDS differential signal is sent to the logic version on the LCD.
In LCD TV repair, when the TV screen fails, if the TV's inverter processing circuit is composed of a non-independent single IC, the fault must be on the circuit composed of the integrated block, or the power supply circuit of the integrated block. First, the first step in the inspection is to check whether the working voltage provided by the external circuit for the integrated block is normal; the second step is to check whether the external filter capacitor of the integrated block has leakage or breakdown; the third step is to replace the IC itself. change. If the TV can be turned on twice and has a grating, the clock oscillating circuit and the reset circuit of the integrated block need not be checked. Because the clock oscillating circuit and the reset circuit have problems, the TV cannot be turned on, let alone the grating appears.
For the frequency conversion processing circuit, in addition to the three maintenance steps mentioned above, in addition to the above three maintenance steps, a via hole between the variable frequency control integrated block and the frame memory is added. The steps to check. Because not only the integrated block itself and the external power supply circuit and the external filter capacitors may cause the screen to be out of the way, the via holes may cause the information of the representative image to be lost, and the "flower screen" failure of the television may also occur. In addition, the pins of these ICs are often quite dense, which is prone to false soldering and lead to flower screens. This is something that deserves special attention. If conditions permit, it can be solved by heat gun repair welding.
In addition to the above problems, I also encountered the phenomenon of flower screen caused by foreign objects in the screen card slot during maintenance. The screen card slot is very small, and the maintenance is not noticeable. It is easy to have fine dust entering and the contact is bad. . Because this is not part of this article, it will not be detailed.
Note: The picture is not very clear, just for the example of this article. The failure examples are often encountered, so I won't go into details.