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repairing a LG model 42lk520

rebel90

Jun 3, 2012
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I have a LG 42'' tv that im trying to fix but im new at this kind of work more of a hobbyist, anyway it will not power up at all it has a small erd light in the bottom right hand corner that comes on as soon as you plug it into a power outlet . now I have had the back off and checked for blown fuses and capacitors they all look ok and i have checked them with my meter which is only a cheap meter not a fancy one like i need , i have also checked the resistors as well they all look to be good as well checked them all , i cant find any burnt marks or discolor to the board . now a guy had given me the tv which is only about 4 months old and he said he thought it got hit with a jolt of lightening any help would keep me from pulling out what hair i have left lol thanks.:D
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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OK, lightning can cause lots of damage, and some could be totally invisible.

It's quite probable that the power supply is faulty.

However, without experience, this is a particularly dangerous thing to be playing with as it has high voltages present.

Looking for obvious damage is the first step and you've done that.

The next step is to check some of the "usual suspects", and for switchmode power supplies that includes the rectifiers and chopper transistor(s).

One quick question... Does the power supply make a single click (or any other sound) when you try to turn on the TV?
 

rebel90

Jun 3, 2012
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hey thanks for the reply , and no it doesn't make any sounds at all .
like i said if i plug it into the power a red light comes on on the bottom right hand corner of the tv , and if i press the power button it tries to fade away but never completely does almost like a real slow pulsating motion.i have look all over the web to see if anyone has had the same issue with this model but so far no luck . I catch on real well to almost anything so i think i can fix this if only i can find the problem .
 

davenn

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Sep 5, 2009
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hi there

with this sort of damage, you are going to need a service manual with the schematics
else you will just be stumbling in the dark

Even then it may not be repairable. the damage could be considerable and as steve said much of it wont be visible .... ie. zapped transistors, intergrated circuits etc.
It takes very little excess voltage to destroy some of these devices

Dave
 

CocaCola

Apr 7, 2012
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intergrated circuits

IMO the worst part about modern electronics... Once you exhaust the obvious physical signs of damage you are left at the mercy trying to diagnose the ICs that are in most cases proprietary so unless the manufacture tells you how to test them (or they are not proprietary) you are out of luck...

Repair for most of these things nowadays is to swap out the entire faulty sub circuit board...
 

davenn

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Sep 5, 2009
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yup, in the end there has been only a tiny handful of lightning zapped electronics that passed through my workshop and went back to the client in a working condition.
prob 90 - 95% were consigned to "file 13"

dave
 

rebel90

Jun 3, 2012
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wow !!! any good news ? lol well that was my fear all alone but like i said i'm only going to have time in it no money so i thought i would give it a try ... oh well thanks guys for all the support and advice, i also read somewhere that it could be the software that has been lost do to the jolt didnt make any sense though ? if i wanted to purchase a power supply board where would be the cheapest place to get it from and do you think that will fix it? thanks again.
 

CocaCola

Apr 7, 2012
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i also read somewhere that it could be the software that has been lost do to the jolt didnt make any sense though ?

That is the problem, you have no way to test, reload or verify the firmware in an IC or the IC's internal hardware and function unless the manufacture supplies this information to you...

if i wanted to purchase a power supply board where would be the cheapest place to get it from and do you think that will fix it? thanks again.

Ebay, manufacture direct or through an authorized repair center...
 

rebel90

Jun 3, 2012
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i checked the fuses but i did while they were still in the board will they read good even if there bad if i read them this way?
 

Bandit6319

Sep 16, 2014
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Sep 16, 2014
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I have a LG 42'' tv that im trying to fix but im new at this kind of work more of a hobbyist, anyway it will not power up at all it has a small erd light in the bottom right hand corner that comes on as soon as you plug it into a power outlet . now I have had the back off and checked for blown fuses and capacitors they all look ok and i have checked them with my meter which is only a cheap meter not a fancy one like i need , i have also checked the resistors as well they all look to be good as well checked them all , i cant find any burnt marks or discolor to the board . now a guy had given me the tv which is only about 4 months old and he said he thought it got hit with a jolt of lightening any help would keep me from pulling out what hair i have left lol thanks.:D
I just aquired that same tv with that same problem. Anyone have any luck with anything before I buy a new power supply board?
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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Clearly power is getting to the power supply. I would follow all the steps that were suggested for the original poster (and it sounds like you have).

Perhaps these TVs have a sensitivity to voltage spikes.

If you can post clear images of both sides of the power supply board we can take a second look.

A new power supply board *might* fix the problem, but it's possible that the problems go much deeper.
 

Bandit6319

Sep 16, 2014
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I'm probably just going to get a new power supply board and hope it doesn't need a main board as well. I've been over and over that power board and nothing that I can see has any damage. I even re-soldered several components that the solder looked questionable. I've repaired several similar tv's and had success, it's a hobby of mine. I will post some pics, a second look is always helpful. Thanks for replying *steve*.
 
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