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No Power In Philips LCD TV Repaired
I received this Philips model: 32PFL3409/chassis TCM3.1 which was dead. From my past experience and bad encountered with cracked LCD panel, I find it worthwhile to put in extra work to check for crack screen before the repair by exposing to sunlight. ( photo 1).
Photo 1 –Checking on the LCD panel for crack.
Under the sun the LCD screen does not show any sign of crack or defect so I proceed with the repair work. The first thing I noticed the fuse has blown on the power supply board. Normally with blown fuse there must be at least more than one parts shorted. Surprisingly, I could not find any shorted components. When I was checking the MOSFET drivers, I noticed that there were two capacitors CW2 and CW4 facing each other side by side with black marks on the surfaces ( Photo 2). When separated, capacitor CW4 showed sign of damages probably due to high voltage breakdown since it is rated at 1KV.
Location of CW2 and CW4 on the schematic
I changed both capacitors CW2 and CW4 to higher voltage rating of 2KV with the same capacitance value. I suspect power surge more than 1KV killed the capacitors. The fuse was temporary replaced by a 100W bulb to test the power supply after repair. When power was switched on, the bulb glowed brightly for 1 to 2 seconds then goes to dim level which was a good sign. The TV sound can be heard but the backlight was not turn on even though the 24V is present and the BL-ON voltage is more than 2V.
I suspected there must be problem with the backlight high voltage inverter circuit .IC10 (OZ9976) is the backlight PWM controller IC. When I measured the input supply voltage on pin 15 the +12V was found to be missing. I de-soldered pin 15 and turn on the power again, the +12V supply line was now back to normal. IC 10 confirmed to have shorted the +12V supply line.
Backlight high voltage inverter IC 10
After replacing IC 10, the backlight turn on and the TV is operating as normal. This is a simple and straight forward repair job. Hope you enjoy reading this article.
This article was prepared for you by SK Wong from Malaysia and he graduated from London with a degree in Electronics and Electrical Engineering. He has more than 40 years of experience in the consumer product manufacturing. With the passion to repair electronic products from young , he has been doing it part time until now.
Currently, he can provide turnkey solutions for consumer products including services from idea or concept to design , prototyping , finished products (including electronic,mechanical and plastic parts) and manufacturing.
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Note: You can check his previous repair articles below: