I got a LG 42LV570S from eBay classifieds for 70€. The seller said that the device wouldn't start anymore and blink. Well, that's not too hopeless. So I thought.
First thing I noticed was that the CPU was clicking in a regular interval and that the DRV-ON signal for the backlight wouldn't go high. All the voltages from the power board were good.
Now, on the mainboard I found one DC-DC switcher with a very strange pulse signal. And because of that, it did not produce the specified 5 volts.
It should look like this (taken from a neighbour):
Peering through the magnifier, I noticed a couple of strange things. A ceramic cap had traces of sparking (yellow circle) and the switcher chip had some dirt flecks on it (red circle). It looked as if someone had dropped some tool on it and produced a short! The inductor (arrow), which is in series with the cap was shot. I measured 12V before and 8V behind it and its resistance was >1k. It should be close to zero.
I salvaged a similar inductor from a dead mainboard. Curious about what came next, I switched the TV on.
Uh oh. This looked as if source drivers #2 and #3 on the panel were dead. Dammit!! Also, the right part of the screen's brightness wasn't stable. It continously pumped from dark to bright and vice versa. That was not good at all.
Frau Johansson had some problems with her skin tone..
Ok, with front bezel and panel cover removed I carefully inspected the driver boards. Oh my god. Massive corrosion. Some idiot must have wiped the screen with a wet cloth. Driver #6 and #5 looked very bad. #4 and #1 seemed ok. One ceramic had been so badly damaged that it even lost one of its contacts. Cleaning and resoldering the mess did not help.
Oh dear, the reason for the vertical blocks of #2 and #3 revealed itself. A burned trace on the flat cable. It had molten a hole into the plastic. That was it, no hopes to get this TV fixed.
Driver #1 almost didn't make it:
I bought a piece of junk with a mysterious history. I am not sure if the seller screwed me, however it is impossible that he had not seen the panel defects before (he was using the TV), because the mainboard problem must have occured afterwards. Bastard.
At least I can sell the boards, which should all be ok, for more than I paid for the TV. The mainboard alone is worth 100€.
And once again, the panel puzzled me. This one had no gate drivers on the sides! Just the six source drivers on the bottom, which therefore must be some fancy combination of both. I just don't understand these things. :-( I'd love to crack one open and study how it is wired, but that's not likely to work.
Looking into the micro world of the panel
So here they are, the gate drivers! They live on the glass plate. Those delicate structures must be semiconductors. Amazing. A couple of thin traces on the top go to the driver boards.
My next gadget will be a decent USB microscope :-)
