First of all, looking at the negs I see a lot of bleed between frames and the rebated edge on the overexposed frames. To me that says that if you changed nothing between the good shots and you see this overexposed result, you have a camera failure. Looks to me like the shutter is sticking or the aperture is sticking. Look into the lens from the front and the back with a magnifying glass and see if there is oil on either the aperture blades or the shutter blades. Most probably the shutter is causing the problem.
Secondly, take the camera and open the back or remove the back and aim the camera at a table lamp or some light source (illuminated white wall) and run twenty to forty exposures. Look into the back of the camera and get some sense of the amount of light you are seeing and then run the exposures. You will be able to see a much brighter 'flash' if you have a sticking shutter or the aperture blades are not closing. Between the lens shutters are extremely vulnerable to the slightest bit of oil. If the camera were left, for example, in a hot car during the summer months, the oils/grease will migrate from the focusing helicoid into the shutter blade/aperture blades. If it is not a migrating lube problem, then I would suspect a failure in the electronics.
Be sure when peering through the back of the camera to try all exposure modes including manual to see if the auto modes may be failing. Hopefully, this way you will be able to isolate the reason for the heavily overexposed frames. Also, try and duplicate the shooting situations you encounter by running the open back test outside. It is more difficult to evaluate in bright sunlight since your pupils will be closed but with that much overexposure you certainly will see a difference. Try different apertures, such as 16, and run a batch of dummy exposures. F16 will be obvious when you look through the back. If it fails to close down, you will see it immediately.
Lastly, doing the open back exercise may help if it is a camera that hasn't been used much. I typically will run a 100 open back exposures at all apertures and all shutter speeds with a new(used) camera just to exercise because most cameras I buy are likely to have been sitting in the closet and not used for a while.
It is definitely an exposure problem with the camera. Now it's up to you to find the issue! Good luck!
Last edited by Fred Aspen; 02-28-2013 at 08:43 PM. Click to view previous post history.