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OK. This makes some sense. I have found that the vertical hold becomes unstable when a scene changes - especially if a scene in the picture becomes a nighttime scene with an abundance of black. I also see it occur when for example, when a tv program goes to commercial: the commercials tend sometimes to be less stable than the program pictures, of if watching local news, the studio shots are more stable, but when they go to a reporter in very "contrasty" setting again the hold decreases. Some times in fact, you can go to no vertical lock at all, going from upward to downward roll by the slightest adjustment of the vertical hold control. Change scene, and it'll lock right in.
I also notice it once in awhile if I'm playing a DVD however the video out on the DVD runs thru an image stabilizer to remove any kind of copy guard interference which could affect things, so overall watching DVD's are the most stable. If I run my cable thru the image stabilizer it has no effect.
When I first restored the set I was able to make the vertical hold more stable by swatting the sync separator tube but I didn't touch the noise inverter / vertical output tube. Perhaps I'll take a look at that next.
-George-
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