Locating the problem
After unscrewing couple screws, the power/inverter board can be removed and unplugged from the scaler. Interesting thing here, LG opted for this black PVC thing to provide insulation between the board and the metal chassis of the LCD panel. So you also have to remove that if you want to solder anything. It holds on the board via two plastic teeth.
As you can see, the board is kinda darkened under the inverter transformer. There are some drilled holes to provide some tiny airflow around the transformer, which are made pretty useless when there is that PVC cover over the whole board. Oh well. This transformer is the EEL-22W, which is one of a few which go bad the most, so it is always a good idea to check if these are still good by measuring ohmic resistance of both its secondary windings.
Although in this case, the problem was as in most times – bad crapacitors. It was something like Su’scon or other garbage brand. There are two rails on this power board, stand-by of +5 V, and +22 V for the inverter. It can often happen that the caps for the inverter board go bad first, in this case it was the stand-by rail which feeds the logics on the scaler board, hence the W2252TQ appeared to be completely dead.
Since I have quite a number of old caps of trustworthy brands in good shape, waiting to find a new home, I used three 1500μF/6.3V ones and five 470μF/35V (three replacement ones and two in the vacant spots) ones so the actual capacity rises somewhat, as I usually do these things. Could have used new ones too, like Chemi-Con KYB 1000/25, but then the capacitance could be a bit too high, this should be enough to last more than another decade (if the backlight survives as long).
So after reassembling everything together (don’t forget pieces like the metal cover of the lamp connectors, and especially the metal reinforcement of the stand mount, like I did 
), it should run as a new one. And hopefully, happily ever after
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