Electronics > Repair

LG TV turns on for a sec then shuts off...

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Lockon Stratos:
Sup fellow electron hunters?

Hoping to get some help with an lg tv. This is what it started doing:
https://youtube.com/shorts/KUAGAYy5ino?si=JYt8iiQ_Yxo3BloC

Data sticker:
https://content.section9.me/im/eev/lg_tv.jpg

It turns on for a brief second, emits some abnormal sound then shuts off completely. Even the red led cuts out so i assume the PSU shuts down for some reason. Cant see any cap juice or blow-holes so im pretty much at a loss where to start.

Would appreciate any help. Thanks!

u666sa:
I'm thinking backlight. YES, when backlight is broken it would actually come on and turn off.

There is a way to disassemble the screen. You check backlight LEDs individually using a power supply by providing some voltage to them. If at least one LED is burned that means you have to replace all strips, otherwise you'd be diving into it soon one more time. However, each LED can be desoldered and replaced individually.

inse:
Spash screen looks quite normal though

Lockon Stratos:

--- Quote from: u666sa on December 22, 2024, 08:06:05 pm ---I'm thinking backlight. YES, when backlight is broken it would actually come on and turn off.

There is a way to disassemble the screen. You check backlight LEDs individually using a power supply by providing some voltage to them. If at least one LED is burned that means you have to replace all strips, otherwise you'd be diving into it soon one more time. However, each LED can be desoldered and replaced individually.

--- End quote ---
Measured the 2 strip (2 set of red-black pair coming out) and both measures ~3,1V. So no shorts there. Ill take a look properly tomorrow.


--- Quote from: inse on December 22, 2024, 08:11:02 pm ---Spash screen looks quite normal though

--- End quote ---
Yup, thats what puzzles me. If one of the rails had an issue (either for the logic or for the backlight you would think it effects the image as well.

Took out the PSU and now that i have it under some proper strong lighting i think i might have found a clue (or its just some dirt or something):
https://content.section9.me/im/eev/lg_tv2.jpg

/edit
https://content.section9.me/im/eev/lg_tv3.jpg
Blue thingy cracked on the bottom, sneaky little devil. Markings: RR 101K 1kV 70. A MOV maybe? And yes i went medieval on it and cut it out after i noticed the crack, still doing the same thing. The pink resistor right next to it measures 0,148 ohms in both directions, if im not mistaken while decoding that should be a 30,8 ohm resistor. Diode mode shows dead short.....

inse:
Its a 100pF 1kV capacitor, probably from a snubber circuit.
Not advisable to run the power supply without it.
The resistor looks like orange-black-silver-gold to me, which translates to 0.3Ohms 5%

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