in my Zenith 20XC136. any pointers on where to look?

I cant get rid of them not mater what the settings, diagonal lines (RGB) grouped closely together, groups are spaced about 2" apart the full screen.

Very dim, but alway there (there intensity does not seem to change so more noticable in dark scenes.

My guess is... did the screen control on the flyback get moved? I've seen that control get flakey-intermittent too and need rotating back-and-forth a few times to make good contact, then set it til the lines disappear, I assume this set has a focus and screen controls on the flyback assy, if not, disregard!

(I had an NEC 30" set that needed a little tweaking to the screen control a couple of times in its 20 years of service, same symptom)

nope my bad, I had the CRT brightness range turned way down (during an early battle with blooming). After I reset the brightness range it all cleared up.