I should have been more specific on what I was doing in the video. The beginning of the video is showing a blank screen because I have paused the source. The vertical lines are way easier to see when there's nothing on the screen. I am adjusting the potentiometer in one direction and at second 3 you can see the vertical bars stop and start moving in the other direction. Then at about second 6 I start moving the potentiometer in the other direction and you can see the vertical bars stop and move back in the original direction. Then at second 11 I played the source video again so you can see the problem isn't vertical hold in the set itself. The set lost vertical sync as you can see, but the bars are "in front" of that. I continue to adjust the potentiometer with the source material playing.
I'll shoot another video and give a play by play voice over of what I am doing.
Here's more of the TV circuit. I am injecting at pin 1 of VT-6A below and have removed the output from the detector that was going there.
Pin 3 of VT-6A goes to pin 6 of the seven pin plug P7.
