The device's production year is 2011. I did not suspect any faulty caps in it. From what I have seen in LG TVs so far, this is not a likely fault, even more so after a little more than three years.
Nothing special under cover (no plastic, nice one). The usual. The cover is made of steel, I guess this is to give the very flat TV more stability.
Ok. First test all the voltages. 3.5V standby, 12V, 24V, all there. The backlight voltage was only 36V and is supposed to be 64V. However, the DRV-ON line was low all the time, so the backlight was never activated. Nevertheless, I checked all diodes and FETs for shorts and the electrolytics for ESR. No findings.
I used two 10k pull-up resistors to let the power supply activate all voltages. The main board was disconnected. One R between STDBY and PWR-ON, another one between STDBY and DRV-ON. And lo and behold, the backlight turned on.
The power supply was flawless. It had to be the main board. So, next, I checked the voltages at all the swiching converter's output inductors. Nothing extraordinary. But what's that? An electrolytic capacitor with no voltage at its plus leg?
This is the schematic from the service manual:
It ought to have 24V! Something had to be wrong with the inductor between the 24V line from the pwr supply and the cap.
When I put the probe of my multimeter on the solder joint (red arrow) sparks where flying. Wow. This joint was severely broken. I reflowed it and , Frau Johansson looking good again:
I think the problem here is the glue, which is supposed to secure the white socket. It covers one side of the inductor and so this side is more rigid than the other. The mechanical stress of expanding through heat and shrinking while cooling down affects mostly the side without the glue. This will eventually break the solder. If the inductor could expand in both directions, this would probably not be a problem.
One last easy job was left. The power button on the remote did not work. Whiping the black contact surface and the rubber button with cleaner fluid fixed it.
This is a good TV. Nothing extraordinary, but it has a very solid picture with pleasant colors, and an acceptable sound. It sports two expert modes for fine adjustments of white balance and colors. And it looks good. LG manages to build middle class TVs, which look nice even though everything is plastic.
(FROM:alpengeist-tvrepair.blogspot.com)
