Found one - look for Official Reign's YouTube channel, this video: "How to add Firmware Update/Sega Genesis Flashback HD 2018".
Scroll down to the comments, expand the correct comment thread and you'll have a link to the img file.
Awesome.
Hey, I'm late to the party and seems like I missed the latest Sega Flashback HD 2018 firmware update that allows the use of the SD card...can anyone share this file?
Thanks!
I just registered to this forum to thank you for this excellent post...
Very well detailed explanations and pics.
Results are fantastic.
I used this to restore other buttons I also had experiencing trouble with.
Very much appreciated.
The best from Mexico.