I have a Pentax 645N. The camera works, but the shutter speed knob on top of the camera is broken. I shoot the camera in Aperture Priority and adjust the shutter speed using the exposure compensation knob. There are no parts available, so the camera cannot be fixed.
I wanted to replace the camera, but my budget would not allow the purchase of another Pentax 645N. While researching, I saw that the earlier version was a few hundred dollars cheaper. It does not have many of the features of the 645N. The Pentax 645 only has Center-Weighted metering, while the 645N has spot, center-weighted, and matrix metering. The 645N has autofocus and allows for 1/3 of a stop exposure compensation, while the 645 does it at full stops.
Last Saturday, I left home around 7 AM to catch the early morning light with the new camera. I discovered another difference between the cameras. The Pentax 645 shoots 15 frames per roll, not 16 as the 645N does.
I enjoyed the experience and look forward to using the camera for the rest of the year. I developed the film in HC-110(B) for 7 minutes @20C.