It is almost certainly something physically wrong with the camera, because the image tails off into black smoothly and this is extremely unlikely to happen with any kind of digital problem.
If you are using flash then this kind of symptom would be very characteristic of using too fast a shutter speed, assuming the shutter is vertically-moving (I don't know whether it is for this camera). But this would only occur for flash pictures.
If you are exposing images under flickering light then you can get partial stripes like this but you would expect them to appear at random places across the frame: if they're always at the top this isn't it.
If it occurs for all pictures then it could either be
- a problem with the shutter, assuming the shutter is vertically-moving (if it's not it can't be this);
- a problem with the mirror.
It's probably more likely to be the shutter I think.
If the camera has an option to lock the mirror up you could distinguish between these: lock the mirror up and then take a frame: if it has this problem it's the shutter, if it doesn't it's the mirror.
In either case it needs someone to look at it I think.