How to inject a signal into a TV?

[ChrisW6ATV]

Originally Posted by wa2ise

Video signals have a polarity, and you can have it be upsidedown. Not upsidedown as if the vertical yoke were wired backwards, but the video looking like an old fashioned photographic negative. Whites being black, blacks being white, and so on. Also the sync circuits won't sync up.

While recently testing my RCA CTC-4 chassis, I saw exactly these results. I injected video just past the video detector diode from my Sencore VA62 Video Analyzer, which has a drive control that varies from several volts positive, through zero, to several volts negative. I could see the unsynchronized, reversed video in the positive direction, and correct video in the negative direction that increased in contrast and synchronized as I increased the negative signal voltage.