Not sure if I'm doing this right, but here is the +285V line at the junction of R249/R250 near the 3.58 oscillator tube, with no signal at the receiver:
When I turn on the color bar generator, the trace changes to this:
The traces are somewhat cleaner than what appears in the photos; both of them bounce up and down a bit on my scope.
I got similar results when scoping that line at its origin (junction of R266/C117B in the p-s) and at pin 2 of V117, the horizontal oscillator.
Phil Nelson