I'm too lazy to go through the technical documentation the TS has provided - but whether its a dual beam or a dual gun scope determines where to look for the fault.Ok, thanks for the photos.
Everything seems clear now.
It appears that the Channel 1 input amplifier is shot, i.e. the amp output is way off the screen.
Or maybe the Channel 1 vertical position control is at fault.
We will have to take a look at the schematic. I have to take a break for a number of hours (time-zone difference).
In the meantime, have at look at the Channel 1 circuit board and see if you can post some clear pictures (if you haven't already)
Edit: You did mention in your first post:
6) Traced calibration signal input to CH-1, to C106 and notice signal drops to negative DC bias, probably a clue there?
Yes, that is a big clue. Will follow up on this later.
With a dual gun CRT, it could be a dud cathode or heater. A dual beam scope either chops or alternates the traces depending on timebase speed. Often chop/alternate is a switch on the front panel, some scopes tie it in with the timebase speed selector, the switching is complex and worthy of examination.