Hello everyone, I'm going crazy with this repair and need your help or feedback if you've worked on this case before. Motherboard model: TPD.RT2841.PB771 LED driver chip: MP3398E (SOIC-16, narrow case) Symptom: When I turn on the TV, the LED backlight turns on normally (voltage rises to about 60V), but after exactly 2 seconds, it turns off and the voltage drops to zero. The sound remains, and if you shine a flashlight on the panel from the outside, you can see the background image (the video processor is active). Tests and repairs performed: Replacing LED strips: I replaced the entire set of LED strips with new parts. The problem persists.
Thermal Analysis: During the 2-second power-up of the board, while monitoring it with a thermal imaging camera, I noticed abnormal temperatures in the low-voltage logic area: the AMS1117 linear regulator (3.3V rail) instantly heated up to approximately 90°C, and the adjacent inductor (labeled 2R2) quickly rose to 70°C. Component Replacement: I tried replacing the AMS1117 3.3V regulator with a new one beforehand. I also desoldered the blue high-voltage damping disc capacitor (LR 471 1kV) located between the large rectifier diodes, thinking it might leak under load, but the board's behavior remained unchanged (the temperature remained high and the LEDs went out). The capacitor was re-soldered.
Checking the driver pins: When checking the MP3398E pins with a cold tester, I found a stable ground connection (GND) on pin 3, while the official SOIC-16 datasheet states that the overvoltage protection is on pin 4. My question: The chip clearly latches, disconnecting 60V after two seconds. Before resorting to the standard overvoltage protection bypass modification by installing a 10kΩ resistor between pin 4 (overvoltage protection) and ground to trigger the protection, I'd like to understand the root cause. Has anyone experienced similar overheating of the 3.3V regulator and coil 2R2, combined with LED driver lockup? Could this be an issue with the SMD resistor divider connected to the overvoltage protection pin, or has the MP3398E become overly sensitive and malfunctioning? Thanks in advance to anyone who can give advice!
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