Chosen Solution
How do your fix/ replace heart rate sensor? Half the time it will flash the blinking heart but never read and the light on the inside of the watch itself no longer lights up. Any idea on cost /process?
@newayulike there are of course no schematics for the Fitbit. You would rely on something like this guide Fitbit charge HR Disassembly to see if there are obviously damaged components. I would probably start with the battery since these error could be originating from a poor battery condition. Fitbit Charge HR Battery
