Ask Slashdot: Recover twenty years old's diskettes

Zilog writes: "The end of the 3½-inch floppy and the disappearance of associated drives showed to me the need to backup the tens of diskettes that accompanied my youth. Carefully preserved, these diskettes have been proved readable for the most part while some are approaching 20 years. However, some diskettes have shown some surface defects in areas with compressed archives (zip). Any idea to recover as much as possible these bad sectors?"