There is a tiny spring on the back of the Janome 7700 APC plate and I believe that is the weak link in that machine as well. If you have your machine back you might take your plate to a Janome dealer and see if it's the same mechanism. If so, the Janome plate will run you about $45 IIRC (to cannabalize for that spring; I don't think it's a direct replacement plate) and you'll be back in business faster.
Michelle