This very detailed guide was originally written by Chris Faulds and used to be available at cfdesign.work/derancilio. Unfortunately, his website is no longer online. Thanks to the Wayback Machine the article is still readable. But since the presentation is a bit wonky, I decided to mirror his awesome tutorial is this gist.
Chris has spent a huge amount of time writing an in-depth instruction on how to take the machine apart, which may also come in handy for other repairs for the Dedica 680/685. Again all credits go to him. Thanks a lot for the great work!
Monday 1st August 2016