LG, M227WDP
2016-01-05 by PETER

 

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Sympton
After the turnon process the image is displayed for 2 seconds and then the LCD gets black. I have measured the voltage in power supply (PLLM-M702A) output connectors for the CCFL lamps, and there is some high voltage there for 2 seconds. I can buy a new board, but I would like to test the CCFL lamps to be sure that the problem is with the power supply board. Any hints to test the CCFL lamps or an additional check that I can do in the power supply board?
Assists PETER
Dear All,

The feeding circuit of the lamps is based on the OZ9938 circuit. I have analysed the circuit and the ignition voltage does not occur before the time of shutdown timer.

I made a simple test to increase the capacitor that controls this shutdown timer. Before this change, after 2 seconds the LCD enters in shutdown. With tha capacitor change it takes a few minutes before it goes to black mode.

During that period, the TV shows a normal image. For times with some interference, but I think it should be related to the inverter operating noise.

What I want to clarify is whether I can conclude that the lamps are in good condition and the problem is the inverter? Or if the inverter operates with some aged lamps this can occur?

Your comments are welcome to conclude if the best option is to buy a new inverter board, or if the lamps are aged, I should focus on the lamp replacement.

Best regards,
Peter
Assists PILI
The problem could be caused by one of the lamps that is cut or improperly welded.
Store LCD
Attends to breakdown