No V-sync on dark screens

[mercifier]

Hi!

I use both an old two-prong vic and a newer cost reduced unit, with the same RF-adapter to a TV set. Sometimes, when the screen is set to black color, it starts rolling, and there's no whay to make it stable by adjusting the TV. The V-sync signal just seems to be missing!

Having the problem with two different TV:s, and (maybe) two different vic's, but using the samt RF-modulator, I assume there's either a problem with this unit, or some common problem to old vics.

Might there be an issue with the level of the black color relative to the level of the sync-signal? There's a lot of adjustable screws in the RF-adatpter, but I have no clue on which of them to touch.

[Boray]

I don't know about the rf-modulator, but I got the same trouble with a video cable when I had adjusted the brightness screw next to the vic chip.