I have taken out my 3DS SD Card and copied some files to my PC a few times (also using my Android phone a few times, which may have caused an issue)
The boot section (FAT formatting) for the SD card was broken, so it wouldn’t mount and the 3DS couldn’t read it (windows disc utility showed it as RAW, meaning no file system, just a bunch of raw data that no device can read)
You can re-write the boot mount (you can “recover” or “backup” lost files, but all the programs are expensive – do not format the card if windows says “can’t read drive, would you like to format”
3DS message: sd card can’t be accessed
Unzip the app – click the EXE testdisk_win.exe – then start a log file, select your 30GB or whatever size of SD card from the list – do a quick scan, then do a deep scan, then scan the boot record entry. The type is Windows/Intel/PC for type, then scan and “write” the boot entry – if the scans are successful you can also “view” all the files in the SD card – it should show some folders ” DCIM Nintendo 3DS ”
Then quit X 4 – and your PC should refresh and mount the drive as normal (made a backup of the entire SD card just in case…
issue with mass usb device sd card android
CHKDSK is not available for RAW drives. (If the drive can’t boot – it is RAW, meaning that there are no files, just a bunch of ones and zeros that the computer doesn’t know what to do with , raw data, but when you fix the file system from RAW to FAT-format with repaired boot sector, it’ll all work as normal.