Tuesday, February 14, 2012

Replacing a Backlight in a DYNEX 19L200a12 HD TV set ... similar to many other flat screens

Many times a flat screen tv or monitor will flash on for a second when it is turned on, and then the screen will go black. Most often, this results from a bad backlight bulb. Generally there are two backlight bulbs, one at the top of the screen and one at the bottom. Their purpose is to light up the screen: without them the screen is black.

Backlights are like the fluorescent lights we use in stores and industrial places: they light up as a result of gas being excited by a high voltage alternating current. A device called an inverter generates this ac voltage. Sometimes the inverter fails, but more often it's one of the two bulbs... especially if you get a screen that flashes on and then quickly goes out.

So if the problem is usually one bulb, why does the screen light up and then go completely out? Why doesn't it just stay 1/2 lit up?

The reason is that the inverter is "smart" enough to shut down if it figures out that one bulb is blown out. That's why you get the flash, and then the darkness... the inverter waits a few seconds to see if both bulbs light; if not it shuts the whole unit down.

Backlights are cheap. With a few bucks, and a whole lot of patience, you can replace them and make your unit as good as new.

Now, what you have to do first is take the back of the unit off (all screws visible from the back side). Of course, make sure the thing is unplugged. Also make sure it is sitting on a rug or something soft so you don't scratch up your screen while you are doing the repair.

You will have to gently pry with a thin, thin screwdriver or an exacto knife to CAREFULLY pry the plastic case apart (once you have all the screws out, that is). Work slowly around the edges, prying it apart as you go.It will snap and pop and slowly come off. Don't force it more than you have to; if it seems stuck check to make sure you didn't miss a screw.

Once your inside the case, you should use a spare backlight bulb to test and find out which bulb is bad. There are two bulbs used in most screens (top one and a bottom one), but you can use either one for testing purposes: You can plug a bottom-style one into the top socket or vice versa. But they won't fit right if you try to install them permanently in the wrong spot. For this reason, I would get both a top and a bottom one if you are doing the repair.

BE VERY CAREFUL that the unit is unplugged between testing the top and the bottom... don't try to plug them in hot. You might get a 500 plus volt shock (unpleasant), but most likely they won't work.

Detach the wire from one of the two backlight bulb sockets, and plug your tester bulb into the socket (and leave the other bulb plugged in). Plug the unit in, turn it on, if you see a long lasting blinding light from your tester then you found the bad one. If not, then unplug the unit, plug your tester into the other socket, plug the other bulb in, and try again. You are not permanently installing these bulbs at this time, just plugging them in and gently setting them down to see if they light and stay lit when you power the unit on. (see photos at bottom).

Remember that the inverter will turn off unless both bulbs are plugged in and lit... so don't ever expect to get a light with just one bulb plugged in.

Once you have found which one is bad, you must unplug the wires that go from the screen circuit boards to the boards attached to the black housing This is so you can remove the housing and work on the screen without the housing getting in the way. You can, however, leave the boards attached to the back of screen alone. They won't get in your way.

Now that you have the screen separated from the housing, take off the 4 tiny screws that hold together the metal frame around the screen. Very carefully pull/pry the metal housing of the frame apart. Use a sharpie to mark each piece because they only fit back in the spot they came out from.

Then very carefully start lifting/prying off the black plastic retaining frame. It's like another frame which holds the screen's layers together. Finally, you should be able to lift the screen up, and then the cardboard white flat reflective thing (I am sure there are better technical names for these parts). You will then see the precious backlight. You will have to  Remove it very slowly and carefully, like a surgeon. You have all the time in the world. You will probably see that it is blackened or broken on one end. Also, it contains mercury and it is very sharp... resist the urge to eat it, as well as be careful not to poke yourself with the sharp poison glass. Note how the wires to the bulb are routed... everything has to be routed the exact same way when you put the thing back together.  

Getting it in there takes an extraordinary amount of patience the first time (. Be very careful. Move slowly and carefully). You can bust the delicate bulbs by bending them, or perhaps even by sneezing on them. Never force anything! If it doesn't fit, step back for a moment, and consider what may be a better way of doing it.

Once you have put your tv together enough to test it, turn it on. Do this before you put it completely together, in case  you missed anything. After that, reverse the order of installation to put it back together. Go slow, and very gently. Don't force anything.


  1. anyone know where I can get replacement bulbs for a dynex DX22LD150A111??? any help is great