The original issue with the Hisense TV model TC25100H was a bright horizontal line on the screen. During the initial diagnosis, I checked the power supply circuit using LA7841, which appeared to be functioning normally. The 5th pin of LA7841 showed a bright signal, suggesting that it wasn't the main cause of the problem. The fault likely originated from the field oscillator section.
Next, I tested the LA76818 power supply and found it to be stable. The peripheral components around pins 23 and 24 were also normal. Based on this, I concluded that the LA76818 was faulty. However, I only had a LA76810 available. Although they are often considered interchangeable, the bus settings needed adjustment for compatibility.
After replacing the IC with LA76810, the screen started flashing. This was due to the mismatch between LA76818 and LA76810, which allowed access to the bus but not the "IC SELECT" option. I decided to remove the LA76810 temporarily, feeling reluctant, and tried adjusting some data close to the original settings, but nothing worked.
I then considered replacing the CPU. The original CPU was LC863528 3PR5, and I had an LC863524 55L7 on hand. After comparing the pinouts, they seemed compatible. The LC863524 55L7 had the "IC SELECT" option, so I proceeded with the replacement.
After installing the new CPU, the screen displayed a full image, though the field was slightly too wide. The screen still flickered, but I managed to enter the bus. The characters appeared white, indicating no color signals were reaching the LA76810. Originally, the CPU output R, G, and B signals through VD736, VD738, and capacitors C775, C776, C777. With the new CPU, there was a 3A 4.3K resistor connected directly to C75, C776, and C777, resulting in proper color display.
Once the TV was turned on, I found the original two-channel video input, but only one channel was active. The volume control wasn’t working as expected. After fine-tuning the bus settings, everything returned to normal. Please refer to the attached images for more details.
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Hisense TV TC25100H replacement CPU example (LC863524 replacement LC863528) - Home Appliances
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