TCL LCD color TV L32M16 damage PFC switch tube and the main cause of the main capacitor - android - Phones Developers

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The root cause of the PFC switch tube and main capacitor damage: a TCL LCD color TV model L32M16, which failed to power on, no display, no sound. According to the user, there was smoke coming out during use, then it stopped working. After opening the case, I found that the main capacitor (100UF/450V) had bulged, and during testing, the PFC switch tube (12N50) was shorted, the fuse was blown, and the capacitor had sprayed. Since the user lives in an area with normal voltage (not 380V), the appearance of the capacitor didn't look like burnt coke, but it still caused the PFC switch tube to fail.
Figure: [attach]255572[/attach] [attach]255569[/attach]
After replacing the damaged components, the machine tested and showed a normal 3.3V output, but pressing the standby button didn’t result in +12V or +24V. Immediately after unplugging, I touched the 120UF/450V capacitor and felt it was extremely hot, almost burning.
[attach]255571[/attach]
Further testing showed that the PFC switch tube was not broken, and the fuse was intact. My analysis suggests that the 450V capacitor overheated due to abnormally high voltage. The capacitor’s capacity exceeded its rated voltage, leading to overheating and failure, which in turn triggered the PFC switch tube breakdown. This indicates that there's a high voltage generation, so the PFC drive control IC itself is likely fine. The issue must be with external components, similar to what happens in A3 power supplies. An abnormal voltage regulation circuit can lead to voltage fluctuations. Referring to the schematic, the PFC drive control IC (L6563 or L6562) pin 1 is the PGC sampling pin. I used a high-resistance meter to check the circuit and found that R861 (470K) was open. [attach]255579[/attach] shows the green resistor below, with color code [yellow, purple, black, orange]. [attach]255578[/attach] According to the schematic, R861 (originally RF12) is 470K and open. [attach]255586[/attach] In other words, when the main voltage is normal, the capacitor doesn’t get hot. [attach]255582[/attach] [attach]255581[/attach] [attach]255583[/attach]
The image is also normal. [attach]255584[/attach] This fault also confirms a case mentioned in a magazine. [attach]255585[/attach] This post is for reference only. Any feedback or suggestions are welcome.

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