Any reason why the O-scope can trigger , because of why? the waveforms are Free running when they aren't in SYNC with the 400hz
The O-scope and the circuit board under test have to MATCH the same MAIN Lines that you plug into the wall?
No it does not! The only time that would apply is if the scope is setup for Line Triggering where the scope uses its line frequency for the trigger source. Assuming Internal triggering the scope can trigger from any source you select. You have things like SOURCE and MODE for triggering. Again, you are not understanding how triggering on a scope works or how to apply it.
Yes I did this and it works, but what is this Called when you SYNC the o scope to a different main line frequency? because it's not sync to 60hz it's sync to 400hz
There is no different main line frequency. There is only one mains line frequency and that is the scope's mains power line frequency. You really need to work on your terminology. The scope triggers from a SOURCE, the user determines the source.
All scope triggering needs a source.
YES! The trigger source!
True you do have to use a AC Step down ratio transformer
Depends on the scope.
Yes what is a good AC isolation transformers for O-scopes?
Again, it depends on the scope as well as the signal, there is no ne size fits all.
Would I need an AC 115v 400hz Isolation transformer? for my O scope?
Do you mean to power the scope? I have no clue what you mean with that statement.