Copied from someone else - I didn't write 99% of what is below but I think it's very useful - especially if you are messing with json files on your UM3 and it stops booting. you'll find a recovery image here: recovery.img. You can install this update by putting this image in a micro sd card - but don't just copy the file there you have to do a special process to make it a bootable sd card. here is a nice guide on putting a disk image on a sd card: https://www.hifiberry.com/build/documentati