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Old 08-11-2012, 07:00 PM   #1
Nimravak
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Default LG 42LH30 with no picture, audio and backlight/screen work

I have a LG 42LH30 LCD TV that suddenly lost the picture. The audio still works and I can switch channels and inputs (though I can't see the menu). Thought it would be an easy fix with just some new capacitors. I opened up the TV, but didn't see any obviously bad capacitors on the power supply board. Testing the board showed that my voltage at the two 5v, the 12v and the 20v were fine. I don't see any obvious problems with the inverter board, but don't know how to test it. There is one suspicious component on the main board (labeled as 3R6), but don't really know if it is just a red herring. If anyone can help guide me on this I would appreciate it

Thanks

New to the forum and first time posting, but learned a lot just going through other threads.
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Old 08-11-2012, 07:06 PM   #2
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Default Re: LG 42LH30 with no picture, audio and backlight/screen work

Your first port of call with a TV with good backlights and audio, but no picture, is that white device on the blue board (T-con) marked "2A"; this is a fuse (possibly 2 amps but seems a little low - typically 3-4 amps for a 42" LCD) and could be blown. You can check it using the ohms range of your meter, it should read nearly 0 ohms (less than 3 ohms would be fine, accounting for probe resistance.) Test with the TV unplugged.

If it is, sometimes replacing it fixes it no problem, other times you will need to diagnose what caused the fault.
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Old 08-11-2012, 09:00 PM   #3
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Default Re: LG 42LH30 with no picture, audio and backlight/screen work

Thanks tom for the reply. Tried testing the fuse (pretty small, so hopefully I did it right) and it looks like I am in the K ohms range (my multimeter does not have the ability to chose the range, it is just auto). I did test it on a few larger fuses on the power supply board, they were all close to 0.

Quick question, when measuring resisters, I thought you had to take them off the board. Do you not have to do that with a fuse? Just trying to learn, so thanks again for the help.

Anyway, if I'm reading it right, it looks like a bad fuse. Let me know if I'm on the right track. It so, I'll try to replace it. But it is so freaking small I might just try to replace the board. Also, you mentioned that I might have to try to find what caused the fault. What would you recommend to dive a litter deeper?

I know I'm a noob at this, but am enjoying the learning process, and really appreciate the help. Thanks again.
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Old 08-11-2012, 09:20 PM   #4
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Default Re: LG 42LH30 with no picture, audio and backlight/screen work

Just uploaded the SM for this set to tom66's site.. hope it helps the diagnosis
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Old 08-11-2012, 10:13 PM   #5
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Default Re: LG 42LH30 with no picture, audio and backlight/screen work

[QUOTE=Nimravak;257954
Quick question, when measuring resisters, I thought you had to take them off the board. Do you not have to do that with a fuse?
[/quote]

With a fuse, you can measure it "in circuit". Your fuse is bad. A good fuse should measure less than 1.0 ohms. Sometimes a fuse just dies to to fatigue.

Quote:
It so, I'll try to replace it. But it is so freaking small I might just try to replace the board.
CuriousInventor makes excellent soldering videos.

http://www.youtube.com/watch?v=3NN7UGWYmBY

PS. One retiredcaps' bonus point for a picture of your Extech multimeter.
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Old 08-12-2012, 04:37 AM   #6
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Default Re: LG 42LH30 with no picture, audio and backlight/screen work

Okay, that fuse is definitely bad.

Next step. Put your meter on the ohms range again and place the black probe in a spare screw hole or press it on part of the metal casing. This is your ground. Then touch the red probe on either end of your fuse (do both ends.) Wait a few seconds for your meter to settle. It should show more than 200 ohms if there is no short on the T-con board.

SM is here: http://tgohome.com/ServiceManuals/?d...&Search=Submit

Last edited by tom66; 08-12-2012 at 04:43 AM..
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Old 08-12-2012, 10:12 AM   #7
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Default Re: LG 42LH30 with no picture, audio and backlight/screen work

Thanks again tom. Ended up in the K ohms range again, about 39.6 K ohms. So looks like the board is okay.

retiredcaps, thanks for that video. Following that, should be able to make an attempt to change out the fuse. Now I'm just trying to find one (probably not something you can find at a radioshack). Would this be an example of what I should get:

http://uk.farnell.com/littelfuse/046...-2a/dp/9943374

Also, tom, you mentioned that 42 inch TVs usually have a 3-4A fuse. Should I get something higher or just stick with the 2A?

Thanks again, and thanks also for the SM.
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Old 08-12-2012, 10:22 AM   #8
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Default Re: LG 42LH30 with no picture, audio and backlight/screen work

Here's a fuse you could use:
http://www.digikey.com/product-detai...4CT-ND/1963359

$1.33 for the fuse (advise you get two in case you lose it, they are tiny!), plus $3 or so shipping (2-3 days.)

That's 3.15A. I almost wonder if it's a design error or planned obsolescence though maybe the newer panels use less. The most common failure is short circuit though, so any fuse less than about 10A is likely fine. If you have a 5A blade-style automotive fuse, you can temporarily use that by soldering wires to it. If the TV powers on with picture, order the fuse.
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Old 08-13-2012, 04:57 PM   #9
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Default Re: LG 42LH30 with no picture, audio and backlight/screen work

Great idea tom. Went out and got a 5A blade fuse and soldered it and... snow! Where before all I had was blackness, now I have something! I'll keep it like this until the SMT fuse comes in.

Thanks again for all your help. Not only did I fix my TV, I learned some electronics as well.
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Old 08-13-2012, 06:00 PM   #10
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Default Re: LG 42LH30 with no picture, audio and backlight/screen work

I tried putting the TV back together temporarily to see if I got a picture, and I ended up with white bleed through on the right side. I don't know if this is just my solder job, or if I did something else. My solder joint on the right side of the fuse (crowded real estate) wasn't the best and it popped once after testing the TV for the first time (after taking the pic above). After soldering it again, the right side was washed out, this time noticeable with "snow" and when I had the TV inputs on. Don't really know if I did something to the board, or if it is just because of the temp fuse job. I'm still going to try to order the SMT fuses and try it, but if you have any other thoughts, let me know.

Thanks again.
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Old 08-13-2012, 11:47 PM   #11
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Default Re: LG 42LH30 with no picture, audio and backlight/screen work

Bad panel, sometimes fixable. Try pressing on the sides of the panel - does the picture improve? Double check your ribbons are seated correctly for both sides on both ends of the panel.
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Old 08-14-2012, 07:58 AM   #12
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Default Re: LG 42LH30 with no picture, audio and backlight/screen work

No improvement when I press on the panel. The ribbons from the T-Con board both seem to be right where they should. I must have done something while moving the TV after I did the temp solder job, though I was really careful when I did move it. TV wasn't doing that before. Kind of a bummer that I fixed the problem, but induced a worse one.
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Old 08-14-2012, 08:41 AM   #13
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Default Re: LG 42LH30 with no picture, audio and backlight/screen work

any solder bridges where you soldered the fuse on? realy good pictures of the fuse area may help us?
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Old 08-14-2012, 01:20 PM   #14
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Default Re: LG 42LH30 with no picture, audio and backlight/screen work

You have good menu function on panel as picture. ---->The main board is good

Check the T-con board

Power on a while

check the temperature of chip AS15-HF normal or extra high temp(untouchable with finger).

Many AUO panel malfunction are this chip NG with high temp.
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Old 08-14-2012, 09:14 PM   #15
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Default Re: LG 42LH30 with no picture, audio and backlight/screen work

Tried to power on awhile, no change after about 30 min. Also, the AS15-HF chip did not seem hot to the finger. I took a couple of pics of my solder job, the following are the best I got. Couldn't see any solder bridges. If you think it is still just the board, I'm might just go ahead and replace it. But if the panel is shot, TV tweaking may be finished.
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Old 08-15-2012, 02:49 AM   #16
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Default Re: LG 42LH30 with no picture, audio and backlight/screen work

the wire you have soldered on the fuse is it bare ie is it touching the top of the surface mount capacitor? looks it in pic 2 maybe stand the fuse upright so its clear of the capacitor to test?
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Old 08-15-2012, 03:29 AM   #17
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Default Re: LG 42LH30 with no picture, audio and backlight/screen work

Quote:
Originally Posted by Nimravak View Post
My solder joint on the right side of the fuse (crowded real estate) wasn't the best and it popped once after testing the TV for the first time (after taking the pic above). After soldering it again, the right side was washed out,.
If the right side came off the smd fuse it was probably live and if it touched down on the "real estate" could have damaged anything it touched. Is there any you can test.
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Old 08-16-2012, 08:21 PM   #18
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Default Re: LG 42LH30 with no picture, audio and backlight/screen work

Got the SMT fuse in the mail today and soldered it to the board, replacing the old one. Ended up with the same washed out area as before. Thinking now that it is the panel itself. Kinda iffy about buying a new t-con board if it is the panel.

Vince, I did make sure that the blade fuse was not touching anything else. It was completely free except at the solder points. Selldoor, didn't notice anything in that area of high real estate that had a problem, though I don't know what and how to test.
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Old 08-17-2012, 02:48 AM   #19
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Default Re: LG 42LH30 with no picture, audio and backlight/screen work

Perhaps see what the panel number is and check what other sets it is in.
Maybe one will come up on ebay/craigs or whatever with a broken panel.
It should be fairly cheap and you might get a working machine to test your panel on and if the same model as yours , a working tcon in it.
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Old 08-17-2012, 03:14 AM   #20
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Default Re: LG 42LH30 with no picture, audio and backlight/screen work

so in picture 9 was the picture washed out then? if it was ok maybe when your tempory fuse came of it may of touched something on the tcon which is now causing this bleed through. if you can pick up a tcon cheap i would try it you have nothing to loose you can always resell it.
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