Experience: LCD TV screen failure causes and treatment - android - Phones Developers

When an LCD TV malfunctions, it's often due to a faulty component in the signal processing circuit. Specifically, if the frequency conversion processing circuit fails, it can lead to display issues such as a "flower screen." Therefore, when diagnosing this kind of fault, the main focus should be on the frequency conversion section of the signal processing circuit. The structure of the circuit in an LCD TV can vary significantly depending on the model and manufacturer. The frequency conversion processing circuit may be built using different configurations: some use two independent integrated circuits (ICs), others use a single non-independent IC, and some combine both types. This variation makes troubleshooting more complex and requires a good understanding of each specific design. For example, in a typical setup found in the Changhong LS10 model, the frequency conversion circuit consists of two separate ICs: MST5151A and K4D2632381. The MST5151A is a control IC with many pins, responsible for managing the inverter function, while the K4D2632381 is a frame memory IC with fewer pins. These two components communicate through various lines—clock, data, and address lines—that are essential for their proper operation. In most cases, these ICs are mounted on one side of the PCB, and the routing of the connecting lines depends on the board layout. Some connections are made on one side of the board, while others pass through via holes from one side to the other. This cross-hole communication is crucial for maintaining stable signal transmission between the two ICs. The digital video signal from the ADC circuit and the VGA input signal enter the MST5151A first. After processing by the frequency conversion controller and the frame memory, the signals are converted into a standardized LVDS differential signal, which is then sent to the logic board of the LCD panel. During repairs, if the inverter circuit uses a single non-independent IC, the fault is likely within that IC or its power supply circuit. The diagnostic steps usually involve checking the voltage supplied to the IC, inspecting the external capacitors for leaks or damage, and replacing the IC if necessary. If the TV turns on and shows a grid pattern, it’s less likely that the clock or reset circuits are at fault, since those would prevent the TV from powering up at all. Additionally, for circuits using multiple ICs, it's important to check the via holes between them. Poor connections or damaged vias can cause signal loss and result in a "flower screen." Also, the densely packed pins on these ICs can lead to soldering issues, such as cold joints, which may also contribute to display problems. In such cases, using a heat gun for rework can be an effective solution. During my repair experience, I’ve also encountered "flower screen" issues caused by dust or foreign particles in the screen card slot. These small slots can easily accumulate debris, leading to poor contact. However, this issue is beyond the scope of this article and won't be discussed in detail.
Note: The image is not clear, but it serves as an example for this article. Such failures are common, so further details are not provided here.