Very dark screen afterswap ( with battery plugged) Fuse help

[juju_paris]

Hello, I swaped my screen with battery plugged and now old and new screen boot with very poor light, but works.
After searching on forums, I found that might be a fuse (F19 or F3?) as there there no inverter on T420.

My mother board is :
Genuine IBM Lenovo Thinkpad 04W2047 T420S T420Si System Board Information
Manufacturer Part Number
04W2047
Model of the unit
T420 T420i

Here is a close up photo of video connector area. I see F19 and F3 inscription. it's a kind of map of white boxes? F3 is bottom left one? Do they change color when burned?
http://imageshack.us/a/img266/4498/gdg2.jpg (230KB 1280x960)

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