Brush headphones are glued shut, and glued well indeed, so there's no practical way to open them to see what happened. I have some dead ones but they will have to be sawed open using either coping saw or Dremel. I really would like to try growing my own crystal element but i can't take that on now. I am really valuing the small vintage earpieces with the aluminum diaphram now, as these have been universally replaced by the new, "de-improved" lower sensitivity ones with brass diaphram.