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

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When an LCD TV malfunctions, the issue often lies in the signal processing circuit. Specifically, if the frequency conversion processing circuit fails, it can lead to display problems such as a "flower screen." Therefore, when troubleshooting this type of fault, the focus should be on the frequency conversion section of the signal processing circuit.

The structure of the frequency conversion circuit in LCD TVs varies depending on the model and manufacturer. Some use two independent integrated circuits (ICs), while others use a single non-independent IC or a combination of both. Understanding the specific configuration is crucial for accurate diagnosis and repair.

A typical example of a frequency conversion circuit consists of two separate ICs: MST5151A, which is responsible for inverter control, and K4D2632381, a frame memory chip. These components work together to process digital video signals from sources like AD conversion circuits or VGA inputs. The processed signals are then converted into a unified LVDS differential signal that is sent to the LCD panel.

In terms of PCB layout, clock lines, data lines, and address lines between the ICs may be routed differently. Some are connected directly on one side of the board, while others go through via holes to reach the opposite side before connecting to the ICs. These connections are essential for proper communication between the components. A faulty via hole or poor soldering can result in signal loss and contribute to display issues like "flower screen."

During repairs, if the frequency conversion circuit uses a single non-independent IC, the first step is to check the power supply voltage and external capacitors. If those are functioning correctly, the next step is to replace the IC itself. However, if the TV turns on and shows a grid (grating), the clock oscillation and reset circuits are likely working, so they don’t need to be checked in that case.

For circuits with two ICs, additional steps are required. Inspecting the via holes between the ICs is important, as a broken connection there can also cause display problems. Moreover, the pins on these ICs are often densely packed, making them prone to false soldering, which can lead to intermittent faults. In such cases, using a heat gun for rework may help restore proper connections.

Another common issue during repairs is dust or foreign objects in the screen card slot. These small spaces can easily accumulate fine particles, causing poor contact and display issues. While this problem is not covered in detail here, it’s worth noting that maintaining clean connectors is essential for reliable performance.

Note: The image is for illustrative purposes only. Real-world failure examples are common, but detailed explanations are omitted for brevity.