The root cause of the PFC switch tube and main capacitor damage was identified in a TCL LCD color TV model L32M16. The user reported that the boot indicator wasn't lighting up, there was no image or sound. During use, smoke came out of the TV, and then it stopped working. After opening the case, the main capacitor (100UF/450V) was found to be bulging and leaking. A continuity test revealed that the PFC switch tube (12N50) had failed, and the fuse was blown. The capacitor showed signs of internal damage, but since the user lives in a residential area with standard 220V power (not 380V), the damage wasn't due to overvoltage. The capacitor didn't look burnt like typical coke-like damage, which led to the PFC switch tube failure. Upon further testing, after replacing the damaged components, the machine showed a normal 3.3V output, but pressing the standby button resulted in no +12V or +24V output. When I unplugged the device and touched the 120UF/450V capacitor, it was extremely hot—almost scalding. I tested the PFC switch tube again and found no breakdown, and the fuse was intact. My analysis suggests that the capacitor overheated due to an excessively high voltage. If the capacitor's rated voltage was lower than the actual voltage being applied, it would lead to overheating and eventually failure. This could have triggered the PFC switch tube to break down. It seems there was a high voltage generation, indicating that the PFC drive control IC (L6563 or L6562) itself wasn't faulty. The issue likely stemmed from external components, similar to what happens in A3 power supplies when the voltage regulator circuit malfunctions. By referring to the schematic, I checked the PGC sample pin (pin 1) of the PFC drive IC. I used a high-resistance multimeter to isolate the circuit and measured the resistance of R861 (470K). To my surprise, it was open-circuited. The original board had RF12 instead of R861, and the resistor was clearly disconnected. This open circuit caused the voltage regulation to fail, leading to abnormal voltage levels and subsequent capacitor overheating. After replacing R861 and retesting, the main voltage returned to normal, and the capacitor no longer felt hot. The image output was also stable, confirming the repair. This case aligns with a previous article that discussed similar failures due to faulty resistors in the PFC circuit. This post is for reference only. Feel free to share your thoughts or experiences. [attach]255572[/attach] [attach]255569[/attach] [attach]255571[/attach] [attach]255579[/attach] [attach]255578[/attach] [attach]255586[/attach] [attach]255582[/attach] [attach]255581[/attach] [attach]255583[/attach] [attach]255584[/attach] [attach]255585[/attach] [attach]255587[/attach] [attach]255580[/attach] [attach]255587[/attach]
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