Changhong rear projection TV CHD4379 after the fire black screen audible fault repair example - android - Phones Developers

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Maintenance Case: Changhong CHD4379 Rear Projection TV. The original fault was a fire in the high-voltage line inside the high-voltage package. The unit was quickly shut down, and the user was advised to replace the high-voltage package. After replacement, the TV turned on, and I heard a high-voltage sound, along with a slight discharge noise. Upon inspection, it turned out that the top of the high-voltage cable had a hole, causing a short. The filament lit up, but the screen remained black. However, there was sound and the characters were normal. I checked the ABL (Automatic Brightness Limiter) circuit and found that the 10K resistor was open. Then I traced back and discovered that the -217V power supply resistor R419, which supplies power to the field scanning circuit, was also open. Additionally, VD312 was damaged, and the -414V resistor R414, supplying power to the pillow correction circuit, was open as well. All these components were replaced. Despite the replacements, the TV still showed a black screen, although there was sound and the characters were working properly. I followed the ABL line further and found another board. Upon checking, I found that the C211 chip capacitor had resistance, which was likely causing the issue. After removing the capacitor with a soldering iron, the boot-up process worked normally. To prevent any future issues, I applied 704 glue to the area where the high-voltage cable had been damaged. Additionally, I added a 20V Zener diode connected to ground on the ABL line for extra protection. The repair was complete and the TV functioned correctly after all these steps.