Help repairing magnetic couplers

I just got some Plarail  Shinkansen with the magnetic couplers in the rear locomotives. Two of them do not seem to be working. One does not stay out. When I let go of the switch it just sucks the coupler back in. The other one would not put the nose back out. I took it apart and was not sure how to put it back together. I was hoping someone on here would have some advice on what might be wrong with them and how to fix them/put them back together!