Hello everyone, I am new here on this forum, and also new to shooting Medium format. I just bought a "like new" mamiya 645 pro on ebay and received it yesterday. I went out shooting with a roll of Portra 400. I took my first shot and everything was fine except the camera did not wind to the second frame. It locked up and would no longer fire the shutter, it just makes a faint click sound. I have tried a lot of different things, like cleaning the electronic connections, and resetting the mirror/ shutter by holding the tiny lever next to the mirror when the lens is off and firing the shutter. Still no luck, it just gets stuck after frame one. I tried taking some snaps on multi mode with the film-back off and it seems to be working just fine. The shutter stays open the appropriate amount, and the curtains open and close. I am thinking it may be the lens back? Anyone else had a similar experience? Thank you!