Replace the Drive's Controller Board.
Inspect the drive's controller board carefully to see if it can be
removed without exposing the drive's platters. Most drives will have an
externally-mounted controller board. If not, stop here.
Find a sacrificial drive. It is important to match the exact same model number and stepping.
Remove the controller board of the failing drive.
Remove the screws with the correct screwdrivers. Most drives use
torx head which is available at home repair stores. Be careful, the
screws are soft.
Learn everything about how it is connected to the drive. Most drives
are connected via ribbon cables and pin rows. Be gentle. Do not crimp
or damage the connectors.
Remove the controller board from the working drive. Again, be extremely careful.
Attach the working board to the failing drive.
Connect the drive to your computer or device and test. If it works,
immediately copy your data onto another form of media or a different
hard disk drive. If that didn't work, try to re-assemble the sacrificial
drive with the working controller board. It should still work.
Rub aluminum foil on the four connectors on the bottom of the failed
hard disk near the center. This will take off any corrosion. Be careful
not to damage any of the pins further to the back. Re-assemble the
failing drive. Try again.