thanks everybody !

someone sent me the schematic by mail : R32 is 2.7Kohms, exactly.

i bought the resistance and soldered it, as well as some other components,
and now my PSU works damn fine ! and the board too, i think i got 2X less
parasites : cool !

but the radiator is still damn hot. is it normal ? never checked before...
(it's an old PSU : 1992)

thanks again
matthieu