Some of the Symptoms of a backlight inverter issue would be:
1. No picture, but has sound and power.
2. Dark screen but you can see what’s on the screen when using a flashlight.
3. The TV comes on and the backlights flash for a second then turn off and the power is still on.
4. The TV comes on and stays on for more than a few seconds then the screen goes dark and the power stays on(you can see what’s on the screen with a flashlight).
I got the TV and when I turned it on, the screen would flash white for about a second and then would go dark. I also couldn’t see anything on the screen with a flashlight. So I open up the back of it and wasn’t expecting the mammoth 8 CCFL Darfon backlight inverter it had. It just lay there menacingly. HAHAHAHAHA But hey, I had this el huge-o TV and I wanted to use it so I had to tackle the beast.
Turns out this TV was using backlight inverter model V144-301 by Darfon. There are many LCD TVs that use this board and there is a known issue with this particular model. One or more of the transformers goes bad.
This backlight inverter repair tutorial will show you how I fixed the Darfon V144-301 backlight inverter. I’ll show you how I tested to see which transformer was bad, how I removed the bad one and how I put the new one on.
Here is what you will need:
1. A fancy multimeter. Well not really, it can be the cheap ones. You just need the resistance or ohms feature. I used a digital Multimeter because the analog ones are menacing (word of the day).
2. A soldering Iron and solder. I used a 25 watt iron from Radiosnatch and it came with the solder.
3. Replacement transformer(s) for the Darfon model V144-301 (I got this thing for $21.99 at lcdparts.com You can probably find it cheaper somewhere else if you want) Get as many as you need.
4. A “Helping Hands” station. I couldn’t have done this right without this freaky thing. It has alligator clips to hold the board while you work on it. Can’t really use the magnifier on it cause you need to use it to keep the contraption from tipping over (because of the mammoth Darfon board). This thing holds my iron and has a little sponge for keeping the tip clean.
5. Desoldering gun, solder sucker, or something to remove solder (this is essential).
I clipped the board into my "Helping Hands" station, set my multimeter on the "ohms" setting and with a range of 10.00 M ohms. Then I took my proby things and tested each pair of little legs on the transformers (I know they are called leads but I’m calling them legs. Accept it.).
There are 8 little legs on each transformer (4 on each side). I started with the top two (1 on each side). I put the black probe to the leg on the right and the red probe to the leg on the left. I did this 4 times for each transformer. What I noticed was that all of them would go from 10.00 M ohms to 0.00 ohms… All except one. Even with the one transformer, only one pair of legs wouldn’t go to 0.00. The reading for the top pair of legs on that one would go all over the place and then settle between 0.03-0.06 M ohms.
From what I was reading, transformers are supposed to have low resistance so I guess it’s not that shocking to even have the 0.06 M ohms reading but I was looking more for ones that were different than the others. So if all of them had a 0.06 M ohms reading then I think I would have had to rule out a transformer failure as being the problem.
Lets get something straight, If it had been anything other than a bad transformer, I’d have been stumped because I know little about electronicals (yeah I just made that word up, and?). hahahaha
Testing a good transformer (0.00 M ohms reading) and faulty transformer (0.03-0.04 reading).
Take your time on this. I can’t stress this enough. You have to get all of that solder off. It is some strong stuff even if you think there is just a micro layer left on the thing. It took me a little while to get enough solder off to move the little legs off the board.
To keep from pulling up the metal contacts (like I did on one) that need to stay on the board, when you have as much of the solder off as you can, gently push each leg forward (prying up will take the little metal contacts off and you don’t want that). Use your iron tip to push the legs forward until all of them are free.
Once you have the transformer off, just look at the little weird thing. Who knew?
If you are like me and want everything uniform, fight this urge and solder the transformer like the others. If you don’t you’ll get wandering readings on your multimeter and end up sucking solder off and doing it again.
Take your time here as well. Put the hot iron to a leg then after a few moments tap your solder where you want it to go. These parts are tiny so you don’t need to jam your solder on the tip and let it melt all over the place.
I would recommend you practice soldering before trying this if you are new to soldering. Actually there are some really awesome instructables on how to solder. Please review them before proceeding.
Once you have all of your legs soldered on, bust out the multimeter again. Make sure all of the transformers have the same readings. In my case all of them now read 0.00 M ohms and I knew I’d hit pay dirt.
Power up the TV with the back off (in case you have to do more resusative work). If your backlights work. WHOOOO HOOOO!
If not… it’s back to the O.R. Check your soldering. You can use the continuity feature on your multimeter (if it has it) and you would be testing just the 4 legs in the middle of each transformer (2 at a time). It should beep. But hopefully it will work the first time because I really don’t have much else for you if it doesn’t. *Smile*
I hooked my small camcorder up to the TV once I got it working.
I’m more inclined to think at this point that these boards may have a solder problem and re-soldering all of the transformers should be done before replacing any of them. After re-soldering, then check transformer readings.