Thanks Irving : about L7824, i thought some people bent this component too much and broke the middle leg ( ground as far as i understand ) and repaired it with a tiny bit of metal included in solder ( that was looking really clumsy )
Anyway, i replaced it with the one from my second board because it looked just better ( can't hurt though )

As a conclusion, because the GBU12G was tested ok, i'm afraid nothing has changed and fuses will blow again.
W'll see !))

Many thanks anyway !!!