After bad attempt to update Raspbian version from Jessie to Stretch my Raspberry PI 3 failed to boot (green LED is blinking 4 times).
I tried to reformat microSD card to install new version of Raspbian from Mac but got problems.
I downloaded Raspbian image, balenaEitcher and SD Card Formatter app for Mac OS. After formatting SD card with SD Card Formatter I launched balenaEitcher, selected image and got green checkbox after flashing as well as one small red dot showing that source and destinations checksums do not match.
Tried with 2 different SD card readers with same result.
I decided to format SD card using terminal on mac.
showed list of drives and I tried to format manually with
sudo diskutil eraseDisk FAT32 SDCARD MBRFormat /dev/disk4
got this error
Error: -69830: This operation requires an unmounted disk
This is list of my questions:
1) How can I validate that SD card has no bad blocks? And if there are any - can I use this card, fix it somehow?
2) What about diskutil error? What can I do to format this card?