When I get a new lens for my Hasselblads, I test it by putting on the lens, taking off the back and prefiring the mirror and for each shutter speed look through the back of the camera at a light to see if the shutter opens and closes properly. I usually hold the release button for much longer than the exposure so that the aux shutter (the flaps at the back of the body) don't close too quickly to see what's going on.
There are many things that could have happened. Are you saying that the negative was black? That may mean that the lens shutter may be sticking open. I occasionally get this on my 2000FCW with my C lenses, but that is for other reasons. When I shoot slide film, the film is totally clear (overexposed). If you just purchased this kit used, it may need a CLA (clean, lubricate, adjust) or as a stop gap measure, exercising the lens shutter sometimes works out the kinks temporarily. One thing I keep hearing anecdotally is that the Zeiss lenses need to be exercised if they are not being used regularly.
If it is slide (reversal) film then completely black means that the lens shutter and or the aux. shutter on the body did not open. It would take a bit more information to determine what is going on. Another possibility is that if the magazine (back) was removed from the camera, the film was wound when a blank frame was already in position. There are too many different situations that can cause this situation. It's hard to tell from the little info you have given.
I've used no flash. The light was always measured with an external lightmeter. I don't know if my mack is an "A" or not, how can I see this? Photos were taken in my garden, with camera on tripod. The time for one shot was 1 s and the picture is perfect. Also my daughter's pictures at 1/125 and at 1/250 are perfect. But other, apparently in a random sequence, are black.
I hope this could help you... to help me!
I once had this problem with an old 250 mm lens which randomly produced black negatives (unfortunately this problem occured on the Galapagos Islands and I became aware of this problem when I was at home and got my films from the lab). It was a problem with the lens. Try your camera with another lens.
Did you use times of 1 second, or thereabouts, on only that one shot?
If you do not keep the release depressed for the entire duration of the exposure, the rear auxillary shutter will slam shut while the lens shutter is still doing its thing, resulting in what could be massive underexposure.
So there's one suspect.
You can see whether your magazine is an "A" type by the presence or lack of a foldable wind crank (as opposed to only a key) on the counter side.
I asked, because in older non-A type magazines, the dark slide operated shutter blocking feature would be lifted as soon as the darkslide was pulled out only a tiny bit. You could then take pictures and only expose the dark slide instead of film, creating beautifully unexposed frames.
Taras' suggestion about the magazine being removed and reattached to a camera in released state is also a good one. It can happen quite easily.
No use of flash rules out the bad PC-contact theory. ;-)
It's always possible that the shutter has an intermittent fault (rather a constant fault showing itself not constantly), not opening now and again. You can check if it has in a very simple way. Take of the magazine, and start firing, the full range of shutterspeed settings, many times. 3 out of 24 is 12.5%, so if there is a fault you should be able to see it within a reasonable amount of test firings.
Either look at the shutter through the front of the lens, or (better) through the back of the camera. You should see the thing open, even at the fastests shutterspeeds.
(And if you are not familiar with the "finger-timed" rear shutter action, see (and hear) what happens when you let go of the release button immediately while firing at 1 sec.)
Weel, you gave me lot of ideas. I want to specify that I've used slide film so black pictures are because of not exposed. I'm waiting to receive an used "volet" for my back so I can remove it and proceed with tests suggested.
I'll let you know as soon as I've tried.