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Geek Culture / Fixing LG's LCD TV - Power PCB

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Sergey K
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Posted: 25th Mar 2013 09:16 Edited at: 25th Mar 2013 09:38
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PCB 68709D0006B
http://www.duycom.com/wp-content/uploads/68709D0006B-PSU-Board-LG-37LC2D.jpg

i have this problem with my PCB
the LCD is not turning on, but i do hear the Relay turning on and off every second. (relay is the black box at center right from that screenshot i gave you, its the one that glued with blue capacitor)
i desoldered the relay, and i checked it under 18 volts, and it does works fine.

so for me, it looks like im not getting stable DC voltage out of some components to replay.

thats what i wanted to know.. what components can cause the problem like i said earlier; turning on and off every second, not getting stable DC voltage to turn on the replay.
Capacitor? or maybe a diode? if its capacitor, then what kind?
cuz its sandwitch pcb board, i cant use the leads to find the problem

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Sergey K
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Posted: 25th Mar 2013 09:38 Edited at: 25th Mar 2013 09:38
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here is a small hint that i disconvered only by the ticking sound of the relay..

it looks like the relay opens and closed when it riches the 18 V but then closing back to about 1 sec.

i managed to build without osciloscope this time line.



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TheComet
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Location: I`m under ur bridge eating ur goatz.
Posted: 25th Mar 2013 09:58 Edited at: 25th Mar 2013 10:02
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I don't see a relay anywhere...

Do you mean this? Because that's a transformer.

http://imgwiz.com/images/2013/03/25/CwN2U.png

[EDIT] Oh, I just realized which one you're referring to now.

Quote: "thats what i wanted to know.. what components can cause the problem like i said earlier"


Impossible to say, there are too many possibilities and not enough information to draw a conclusion.

What voltage do you get on the capacitor after the rectifier? That should be 325 VDC (this will easily kill you btw). What happens if you measure the output voltages? Are they stable?

TheComet

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Sergey K
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Posted: 25th Mar 2013 10:11 Edited at: 25th Mar 2013 10:11
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this one..



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Sergey K
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Posted: 28th Mar 2013 10:13 Edited at: 28th Mar 2013 10:14
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Mystery solved!

i found that 3 capacitors that shown on the picture i uploaded are little bit inflated. so before i just replaced them, i tested the surrounding components.
i saw that those 3 capacitors are around a voltage regulator and i desoldered it and tested it by building a small circuit board.
i found that this regulator doesnt gives the exact voltage it should, and it also heating up too much more than it needs.

so i replaced the regulator, replaced the 3 capacitors and everything worked like new!



and i just felt like sharing my experience for fixing and detecting electrionic problems.

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