OT: Repairing LCD screen that Won't Power On

whoamonga

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I've got an LCD tv a friend purchased back in '06, but it never came on. He never took it back, and gave it to me. I'm trying to repair it, and here's where its at:

The red power light will come on when 120v is supplied to the tv, but the power button does nothing. No attempt at power... I Googled this problem and someone said to maybe replace all the caps on the main power board. So I was thinking of following the 120v lines inside the case and replacing caps wherever they go. Does that sound about right, or does anyone else have a possible solutions?

Thanks much in advance!
 
i had a friend who gave me a 19" lcd computer monitor that was doing the same thing...opened it up, replaced a few bulging caps and it's worked great ever since
 
i had a friend who gave me a 19" lcd computer monitor that was doing the same thing...opened it up, replaced a few bulging caps and it's worked great ever since

I had a DVD player quit and it too was fixed by replacing bulging caps. Lenhit on here also fixed an LCD monitor the exact same way. So you can see a trend that caps are failing, the failure is visible to the naked eye, and swapping out the bad caps fixes it. :)

Good Luck!
 
Damn cheap ass caps from China! Ugh... I've got a Sony LCD that belongs to a friend that will power up and work for a while but then the backlight goes out. I looked at the power supply and it "looks" ok.

Matt
 
If you're gonna pull it apart, just do all the caps while you're in there...
 
wow... seems pretty hopeful that I'll find something in there pretty obvious. If not, i'll just start replacing caps.

Thanks for all the advice, i'll let yous guys know how it goes!
 
This was insanely easy to get to. Looks like the tv consists of two boards: power and interface.

The interface board and the buttons board seem to work fine. I connected a PS2 to the rca inputs and got sound, and was able to control the volume and the channel (presumably, cause the sound stopped).

So i'm wondering if it's not the backlight power. I pulled the power board and gave it 120v but couldn't get any DC voltage going to any of the 6 2-pin plugs that i'm just about certain, go to the backlights.

So here's a pic of the whole shebang, and the power board. No caps look bulging or anything... you guys see any i should start with, or just go after them all?

http://i282.photobucket.com/albums/kk259/whoamonga/misc repairs/lcdviewsonic001.jpg
--that's the back of the LCD tv

http://i282.photobucket.com/albums/kk259/whoamonga/misc repairs/lcdviewsonic002.jpg
--that's the power board
 
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This was insanely easy to get to. Looks like the tv consists of two boards: power and interface.

The interface board and the buttons board seem to work fine. I connected a PS2 to the rca inputs and got sound, and was able to control the volume and the channel (presumably, cause the sound stopped).

So i'm wondering if it's not the backlight power. I pulled the power board and gave it 120v but couldn't get any DC voltage going to any of the 6 2-pin plugs that i'm just about certain, go to the backlights.

So here's a pic of the whole shebang, and the power board. No caps look bulging or anything... you guys see any i should start with, or just go after them all?

http://i282.photobucket.com/albums/kk259/whoamonga/misc repairs/lcdviewsonic001.jpg
--that's the back of the LCD tv

http://i282.photobucket.com/albums/kk259/whoamonga/misc repairs/lcdviewsonic002.jpg
--that's the power board

You check that ceramic fuse right near where the power comes in? :)
 
fuse has continuity. i'm assuming that's good. Plus, the speakers and stuff worked. the little LED light turned green on power-on. I think that fuse is good.

@gamefixer
wow, i had no idea. i really coulda fried up my multimeter at LEAST! But do you think that there's 6 backlights in there? Each of which are using those two-pin connectors? It's funny, they look just like the 2-pin connectors used for the backlight on my mac powerbook i threw in another OT discussion in the game repair forum.

So, make a list of all the caps, order 'em, swap 'em, then try again?
 
quick question about those backlights...

it will be supplying dc voltage to the lights, right? And somewhere in the 3-6k range? I'm not sure i can measure that then... Either way, those lights ain't comin' on. could those high voltage things go bad outta the box, or just go with caps first?

I'm just tight on a first investment...
 
quick question about those backlights...

it will be supplying dc voltage to the lights, right? And somewhere in the 3-6k range? I'm not sure i can measure that then... Either way, those lights ain't comin' on. could those high voltage things go bad outta the box, or just go with caps first?

I'm just tight on a first investment...

I'm not a 100% sure of that voltage measurement but I seem to recall the little LCD Screen on a Beach Head 2000 being driven at 4k or so. As far as I know its DC. I think what craps out on those is the inversion circuit itself. Could be bad caps too but I dont think so.

Matt
 
what is the inversion circuit?

But if I'm not getting any voltage coming out of those 2-pin connectors, would that indicate inversion circuit, or cap?
 
what is the inversion circuit?

But if I'm not getting any voltage coming out of those 2-pin connectors, would that indicate inversion circuit, or cap?

The inversion circuit takes low voltage (probably 12VDC) and steps it up to the 3K (or whatever it is) that the LCD backlights need to operate.

Matt
 
i believe if this was nib and doa, mabye youll get lucky and find a missing trace somewhere or missed solder connection, bent connector header pin, etc etc

could also be the light was just bad or something too...
 
my comp LCD started giving me a bunch of blue and green line artifacts one day. I thought it was junk, but in a last ditch effort, I decided to take it apart (what did I have to lose?), and I do mean, I took everything apart. I used some scrap tools around the house and random bits from a black & decker set I keep in the trunk of my car to do it, which made it even more impressive.

yeah, I seriously just took apart everything in it. removed every ribbon cable and board. it was just the LCD panel left. then I reconnected everything and it was fine ever since.

not sure you'll be so lucky with something so simple like that, however.
 
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