Ok. Let’s try this again…RCA 9TC240 Alignment

[Yamamaya42]

Originally Posted by bandersen

Trigger is not used in XY mode.

You are prob right, but if so, then again, he should get no horizontal activity when the input to CH1 is disconnected.
No input = dot roughly in the center of the oscilloscope
CH1 connected = line sourced from alignment device

And changing the trig source switch (int/line/ext) should have no effect on the dot's movement at all, only input on CH1, if it's working the way it should.

info on scope here.
https://w140.com/tekwiki/images/1/1c/070-3827-00.pdf page 22