I have a 1977 Panasonic Quintrix II set my grandmother gave to me, and I adore it because when it's working right, the picture is gorgeous. Almost like Technicolor color.

It has a problem with the picture. After it runs for a time, the picture will, at random intervals, quickly become very dark. Usually changing channels fixes it, but it is stubborn and I occasionally have to just wait for it to "fix" itself.

Anyone know what this could be? Not sure, but I think the problem could be triggered by onscreen brightness levels.