I think that Save button only affects the LCD screen on the side of the 500. The other things I'd check are that the cable to the viewfinder is securely connected to the camera. Also jiggle the cable and see if that affects the viewfinder. There are 5 controls on the front that adjust brightness etc. Turn them all back and forth a couple of times. Although your camera can't be more than 2 years-old, perhaps one of those controls is dirty and causing the problem.
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