Another option is the TrelloExport Chrome extension:
You may run into a situation where you need to use Trello’s JSON export to locate a piece of information. To do this, we suggest reaching out to a developer—JSON, particularly when it’s covering a whole board, can be complicated to parse out correctly. If a developer isn’t available, you may want to try using an online JSON-to-CSV converter, such as: (This converts to XLS, not CSV)

via Making sense of Trello’s JSON export – Trello Help