LG37LF66 - Distorted image after few minutes - sound ok

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Old 10-04-13, 06:47 AM
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LG37LF66 - Distorted image after few minutes - sound ok

Dear all.. I am a new registered, but have followed some of the threads as a vievew as most of the time they are very very helpful!!!

I need help with my lg37lf66 lcd

I am trying to upload a video but i made it with my phone so it is quite hard!


SYMTOMS:

- I can switch the tv on and everything will be fine for around 30-60 minutes.. no problem, sometimes on distortion after 10 min but for the rest is fine...

- after that time the tv starts to play up, the image gest distorted, hundreds of horizontal lines all over the screen and double image. Occasionally the screen becames black but then he pop back again.

- if the image that need to be shown is all white or basic color the image shows almost of.. but as soon as the image change the distortion continue...

- if i switch the tv off and on again immediately the problem is still there..

- if i keep the tv off for some time and swithc it on again the image is fine..

WHAT I HAVE DONE SO FAR...

- changed 2 blown capacitor on the power supply.
- changed 2 blown capacitors on the backlight
- change the t-con.
- visual chekc of capacitors and voltage as written on the board ( no specific voltage of all componend as i dont know how to do it....

THANKS FOR THE HELP IN ADVANCE!
 
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  #2  
Old 10-04-13, 11:44 PM
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Welcome to the forums from overseas.

I'm afraid there may be more caps. to change. Unfortunately they don't have to look blown or distorted to be bad. As caps. heat up the problem becomes worse.

I use an oscilloscope to check them in operation on the board. Otherwise I would have no idea which ones were bad.
 
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Old 10-05-13, 06:32 AM
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You can leave the back off the tv, and when the problem shows up, use some chill spray and cool off boards one at a time until problem is corrected. Repeat this narrowing the area each time until you find the bad part. Chill spray can be found at most electronic parts stores.
 
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Old 10-07-13, 01:29 AM
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hi guys.. I have a little update on the issue..

I didnt have any freezing spray, so I have used a little fan...

I have managed to find something that seems very interesting to me...

There is a part on the power supply that seems like it has already been modify once... ( on of thoose metal think that are supposed to change dc to ac)...

When i used my fan in this corner of the power supply, the image was going back to normal or at least getting better immediately... Now i cant say 1000% that is this part, infact it could be some of some of the capacitors on the sides...

If there anyway I can check if this part is working properly?! Can i do anything with a multimeter?!

I have attached a pic of the part i think faulty...

https://www.dropbox.com/s/ragvzvkp4o...2016.14.24.jpg
 
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Old 10-07-13, 05:31 AM
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You would need a scope to check the waveforms. I would price the board and if it's cheap, replace the intire board. That would save a lot of work replacing the caps. It's one or more of the caps that is going to be bad.
 
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Old 10-07-13, 05:57 AM
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unluckily i cant find the board very easily..

I have found a few on ebay but quite expensive ( 50) for a try!!

Could any of you give me some advice on where to find them?!

My board item number is :

eax 31845201/13

but I have found

eax 31845201/12

for just 24.. how would i check if it is compatible?!

Please help, i dont really want to spend 50 quind and prob is not the issue either...
 
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Old 10-07-13, 11:45 AM
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In that pic you are showing us the power supply board. The metal thing is a heatsink and removes the heat from the regulators and switching transistors.

I see 4 capacitors in that picture alone. Make sure at least those four have been replaced. Your focus is on large electrolytic caps like those ones.
 
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Old 10-08-13, 04:03 AM
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perfect..

I will start with the big capacitors. As said I have already changed two. Will buy some more and change the rest too.

I have looked into the problem more, and hopefully this can help you t help me.. lol

New details

- If I connect the tv to the power and swith it on everything is fine for a few minute ( and we knew that..)
- If i switch the tv on off and on again.. the green light blinks more than usual.. ( usually it blink 5-6 times, but in this istance is 10+), but then the tv comes on..

-if i switch the tv off and on again more times, the result is that i can hear a electric noise coming somewhere between the tcon and mainboard and the light goes completely off ( so while it blink green it disappear...

- To restore the tv I have to unplug the cable and plug it again....

Any thoughts on this behaviour?>!
 
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Old 10-08-13, 04:23 AM
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Old 10-09-13, 12:59 AM
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That power supply board is running several different power supplies. I can see it runs hot by the color of the board. There are a lot of caps on there that could be causing the issue. I told you to replace those 4 since I thought that was the entire power supply board you were working on.

Without a scope to see the amount of AC ripple you will be just be randomly changing caps.
 
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Old 10-09-13, 08:56 AM
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well I guess I will focus on the area that I have pointed to you, as it is the area that makes the tv work back i point the little fun on...

I will just try this as last chance, if it doesnt work I will just buy another board, hoping that it is the right solution to the problem.
 
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Old 10-12-13, 04:03 PM
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very sad news...

I changed the power supply and the tcon now and the tv does completely the some thing...

works for 30-40 minutes and then distorted or no image...

i am so saaad!

please help!
 
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Old 10-12-13, 04:53 PM
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You may have to go back to your fan. Even if I had the service manual here..... there would still be many caps on the other boards that could cause that fault.
 
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Old 10-12-13, 07:05 PM
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the only board left that I guess may cause the issue is the mainboard...

the problem is that on the mainboard the caps are not the standard omne that i know how to unsold.. they are different.. shorter and they look more professional! lol ( i hope you understand what i mean! lol)

I will go back to my fan! ahahah

will get back with more info tomorrow hopefully good!
 
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Old 10-15-13, 02:15 AM
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hei guys..
i cant find the solution to this problem yet!!!

I tried with the fun.. but could find a specific part that makes the tv back to normal!
Can anyone help me further to throubleshoot the parts?

I will give you as many details as possible.. probably you know what the issue is from this problem...

I HAVE NOTICED....

- when I switch the tv on.. there is a strange continuous sound coming from either the tcon or the mainboard ( they are very close and can t understad wich one makes the noise)

- if cold I can switch it on and off 1000 of times no problem, but when the problem start and i try to swtich it off and on again, the green light will blink forever...

- i noticed.. when i start the tv the image is not sized correctly.. ( is like slighly zoomed) but after few sec i can see a green flash on top/bottom of the tv and the image resizes itself... It happens everytime i swith the tv on!

- then the picture goes bad I can have Horizontal lines, double image, rolling image or black screen!

If it was the power supply.. should i see a short of V output when the poblem start? how can i fine the throubleshoot the problem?
PLEASE HELP..
 
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Old 10-16-13, 04:42 AM
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UPDATE

I have tried what you told me last night...

I used my girlfriend hair dryer to warm up the single boards.

The reaction was not immediate but it seems that it is related to the power supply. I can say what part of it actually is foulty and I can say that is that 100% but I quite sure about it!

The very important bit.. is that I have noticed something that may probably confirm my thought. When the picture goes away ( because If i use the hair Dryer the image doesn't get distorted, it just disappear completely!)

Anyway, going back to my very important bit, When the screen goes away the bottom of the power board, ticks multiple time.. I have tried to understand where the tiocking comes from, but it seems like it come from the yellow think ( i dont know the name) named sj0733.

https://www.dropbox.com/s/ugwgg1wrx6...2016.14.18.jpg

power supply image

Another point, if the image is gone and I put some fresh air on that part of the board, it ticks, and for every tick the screen flicker white ( like if it tried to show the image but can manage to do that!)...

So... What is that yeallow bit.. can I assume is the power supply that fails of it can still be something else that make that bit click?!

thank you for your help!
 
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Old 10-16-13, 05:02 AM
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Earlier in the thread , you said you changed out the power supply board. Two boards having the same problem is very remote.
 
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Old 10-16-13, 05:11 AM
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well bear in mind that the power supply was not new, but bought from an online shop... ( they offer refund and warranty ).

What problem could it be? can it be the main Board?! how can i check this parts? ( the t-con was also bought used..)

thank you for the help..
 
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Old 10-16-13, 11:31 PM
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You are most likely causing the power supply to shutdown on overheat. That ticking is the sound of one of the power supplies starting briefly and then shutting down again. That part you are asking about is a transformer.



Like I said earlier in the thread.... the only way to truly diagnose the problem is with an oscilloscope. Without that you are only guessing...... and there are a lot of parts to guess at.
 
  #20  
Old 10-17-13, 09:21 AM
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The only thing I really want to do is understand what piece of the tv is not working.. I dont want to repair it myself anymore, i just want to know what card is broken and buy it.

I checked the volt output yesterday before during and after the image disappeared and it was completely the some.. no drop in output at all...

if you have any advice please give me some.. in the meantime i will keep you updated with any change..
 
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