A 29-inch Skyworth HDTV was brought in for repair due to a fault. Upon opening the casing, it was discovered that the circuit board had a large burned hole, and the digital board was declared faulty. Since local availability of a digital board was limited and repair wasn't feasible, the decision was made to replace it with a common universal motherboard. As the TV used a dual-focus tube, the first step was to replace the tube holder with one suitable for a dual-focus tube. However, the standard high-voltage package was single-focus, which didn’t fit properly. To solve this, the two focus poles were connected together. After connecting all the plug-in components and powering on, the line output produced a squeak. When the deflection was pulled out, the screen showed normal, but when another deflection was used as a load, the performance was abnormal. This indicated that the issue was related to the line deflection, likely due to excessive load from low deflection resistance. To address this, an impedance-matching transformer was found and connected to the high-voltage package. Once connected, the picture finally appeared, but no matter how it was adjusted, the image wasn’t satisfactory. This led to the idea of modifying the deflection coil. The deflection yoke was removed, and upon close inspection, it was noticed that the two row deflection windings were in parallel. So, the connection method was changed to series. The process involved soldering the ends of the row deflection coil with a soldering iron, then dividing them into four leads. It was important to note that this particular coil was wound using three strands, each made of multiple fine enameled wires, and they needed to be kept intact without scattering. Using a multimeter, the coils were grouped, marked, and then the ends of different coils were connected together while the other two were connected to the deflection line, effectively changing the parallel connection. After reassembling, the image was small and X-shaped. The coil was taken apart again, and the head and tail of one coil were reversed. This time, the picture looked normal! After carefully adjusting various parameters, the result was very satisfactory. A long test confirmed the success. Replacing the board in this high-definition TV was a bold attempt, and others who need to repair HD TVs by replacing boards can refer to this experience. Don’t fear HD TVs just because parts are scarce. In a last-resort situation, even an HDTV can be repaired with a universal motherboard. If you found this helpful, feel free to support it.
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