Example, this is what is going to my GE color roundie G1, with color turned down, (21fjp22)
https://imgur.com/BSJ5KpG
and color up
https://i.imgur.com/5eI2bqn.jpg
IF I pull the horizontal blanking tube or the Y-AMPS, I-E anything to cause it to stop that pulse from getting to G1, I lose raster, BUT, can still get a dim line when setup switch is in service mode, ( no vert )
I have seen the same thing happen if I pull the 1st video amp tube, I lost all raster, same with the video output tube, it had loose socket contacts, and had a habit of losing heater voltage, AGAIN, when it did, I lost raster, but voltage did not change much at the cathodes or G1, this tells me that voltages alone are not enough to get a full raster, at least from what I have seen, are you able to get a line on the screen if you set it to service mode?
A good example is this,
https://www.youtube.com/watch?v=FpOD9g2dKjY
the crt was getting HV and some voltages 400 and up, but due to a LV power fail, it was missing signals that it needed to display anything, and would only show a line in setup mode.