I followed the instructions as described but after clicking the start button in the window "disk USB check" with correct errors in the file system automatically checked, for some seconds the program starts doing something little on the external hard disk
and quits. The window Check disk disappears; no message, no error message, no report.
The USB hard disk is a Toshiba 1TB I checked extensively with Data Western Digital Lifeguard for Windows (took about 12 hours) but found non physical problems.
I located the corrupted file but cannot delete it or do anything with it.
The cause for the damage is most likely that I pulled out the USB plug out of the laptop before writing was completed.