[Electronic M]

If you have the video testpattern generator, then you can test it by connecting the video out leads to the video input jack on a modern TV.

If the video generator works the next thing I'd do is connect it to the side of the video detector diode in the monarch that feeds the video amp(s) and see if you get video.
If you do then concentrate your search on everything between and including the antenna terminals and the detector. If you don't get video then focus on every thing between the detector diode and the CRT.

Hope this helps.

Tom C.