Thank you very much!
At least this did work. I remembered this externally exposed pot as for adjusting the height of the image or something like that. But it can actually be used to stabilize the vertical signal!
However, my main problem seems to be that I’m only receivingthe signal very weakly. It even seems like the channel indicator is still kinda breaking through. I’ve now tried it with a VHS recorder to rule out an error with the HDMI-to-RF converter, even though that works on another TV. It’s puzzling.
(Sorry for vertical video syndrome but it was the most efficient way to bring both into the same view.)
https://drive.google.com/file/d/1g8L...w?usp=drivesdk