LG W2246 Caps/Inverter?

You have a unbalanced load at the lamps, it uses a royer oscillator circuit or something similar. I have had caps that are bad on the inverter, but most of the time it doesn't really affect operation of the unit.

I would check the transformers and lamp drive chips, replace the caps if you feel more comfortable doing that to eliminate that from the problem. They are cheap and usually there isn't a bunch of them. Usually you can use the caps for a ground point and test the lamp drive chips for shorts, they almost always short out.

The flashlight trick will work if you have a place on the panel that will allow light on the tft screen. I use a amp meter to prove that. You can actually disconnect the tft panel and see a different current draw, tells you its working without having to use a flashlight. Or you can take the panel apart and usually see the picture (not recommended).

Would also take a good look at the power supply, if your going to work on it might as well work on the high failure parts.

 

Usually they are 8 pin chips. One side is the input and feedback, the other side all 4 pins are on input of the transformer. I usually just find a capacitor and hook a clip lead there and then to my meter (the ground side). I would assume you have a digital meter, put the meter in diode test then test all the pins on the input side of the chip, not the one connected to the transformer.

This is where having knowledge of using a meter will help you. Look up the datasheet for the chips in question. Sometimes these will blow a hole in the chip making it easy to locate, sometimes it looks just fine but is still bad. Just check each one for a short.

Testing the transformers is a little different, you can still use a meter, but its not a very good test. I use my scope as a function generator to test these, again not a great test but much better then a meter. If you have a scope and would like to try this I will post again on how to use it for testing the transformers.

 

1. Inverter board, cables on side should connect to the lamps
2. Power supply
3. A/D board analog to digital

Cable going from A/D board to inverter will be your Vcc, brightness, and switched voltage.

 

I can't read the schematic, the dpi setting is too low when I print it out.

Inverter and power supply is on the same board. You need to find the Vcc and switched voltage for turning the inverter on. Transformer seems to be good by what you have said. So that leaves a problem on the inverter or the lamps.

Don't mess with the long board. That will not be your problem.

 

I think you have your meter set to DC, and should be AC. Transformers block DC and pass AC.

Yes you could buy another power supply/inverter. An indication the lamps are going bad is a red tinge to them. The lamps will turn on, but if one is drawing more then the other it will shut down.

Also, make sure you hook the meter up before you power the unit, if you try to test it while power is on it will shut down.

 

Since you have another monitor, I would take an use the lamps from the other panel for testing. Size of the lamps don't matter for a short test, but if the screens are different sizes I wouldn't let it run longer then 1 minute. Don't remove the lamps from the other panel, just use the panel next to the other panel.

Notice that there is a gate, drain and source. They are numbered 1 and 2, just use your meter in diode test. I don't have this particular chip, but you will be able to turn it on an off. It will check like a diode until you turn it on, then it will act as a short. Desolder all the drains on the one side of the chip, or if easier for you remove the complete chip before testing.

I will give you a example for testing this component. I used a K2698.

Meter in diode test mode.

Black lead to Drain, Red lead to Source should test like a diode. Remove Red lead and touch the Gate, return to the Source it should now be shorted. Remove the Black lead from Drain and touch Gate and then back to Drain and it should test like a diode again. Test both on the chip and see if one is bad.

If it turns out to be a lamp, I can provide you with the lamps, be careful with the rubber boots. They break easily from the rubber fusing to the lamp. I also have those depending on which one your require.