dos disk repair on Linux

 https://askubuntu.com/questions/147228/how-to-repair-a-corrupted-fat32-file-system

So, either

sudo apt-get install dosfstools

sudo dosfsck -w -r -l -a -v -t /dev/sdc1 

or

fsck.vfat -a /dev/sdc1

fsck.fat 4.1 (2017-01-24)
Logical sector size is zero.

https://ubuntuforums.org/showthread.php?t=1908329

Apparently

testdisk is the solution. 

Disk /dev/sdc: 232.91 GiB, 250059350016 bytes, 488397168 sectors
Disk model: External USB HDD
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x4d2b50bb

Device     Boot Start       End   Sectors   Size Id Type
/dev/sdc1  *       63 488392064 488392002 232.9G 83 Linux

(In this case, found that the partition had been overwritten by a linux partition :)