What's the difference between a 1Khz waveform sync to a 60hz external signal VS a 1Khz waveform sync to a 400hz external signal?
How the scope behaves depends not only on what sync is selected (60Hz or 500Hz) but also on the sweep rate selection and on the trigger type (AUTO or NORMAL). All I can say in general is that when 60Hz is selected, the sweep will be triggered 60 times per second and if 400 Hz is selected, the sweep will be triggered 400 times per second.
It's the same frequency at 1Khz waveform , the only difference is the Sync frequency ( external signal )
Yes, it is the same waveform, but it looks different when each sweep of the scope display starts at a different point in the 1kHz waveform. That gives the display the free-running appearance.
What's the difference between triggering and Sourcing?
Sourcing is the synchronization , the O scope is defaulted at 60hz, the horizontal bean circuit is going across the display at 60hz[/quote]
Well, I've never heard the word "sourcing" used in that way before. But if that is what you mean, then it sounds the same as triggering. But I should point out that the scope does not default to 60Hz triggered sweep. It is just that for convenience, they make scopes that have AC Main and one of the trigger sources, since it is often the case that the circuit your are scoping has waveforms that are synchronized with the AC power supply. Other than that, the selection of 60Hz through the AC Main selection is just like any other external trigger source.
If I brought you a circuit board and had 10 outputs waveforms and I didn't tell you what the line or sync frequency was , how would you know what to SYNC , SOURCE, TRIGGER the O -scope to?
I might start by studying the schematic of that board to see if I could figure out what those waveforms are supposed to represent. If the schematic was not available, I might start from my knowledge of what function this circuit board is supposed to perform. If I didn't even know what the board was supposed to do, then I would probably give up.
[/quote]How would you find out what the signals that are periodic with a period that is related to that SYNC frequency? the frequency/time of the waveform is not the Sync frequency[/quote]
Trial and error. I would try various sweep rates and various sync sources until something made sense.
How would you find out the external signals frequency without me tell you what is it?
Instead of any EXT sync selection, I would select Internal so as to use the waveform I am displaying as its own sync source. Then I would try various sweep rates until I could see one cycle of the signal displayed. Then I could estimate the frequency from the measured period on that display.
What would you call it a clock or what would you call it since it's not really a clock? what is the right name for it?
I might call it a clock, or a sync signal. But what difference does it make what I call it?
True, Since the waveform is no superimposed, what would it be called?
I would call it a waveform that is displayed with an external sync.
Why does it matter if the circuit is reference to ground or floating? what would it change?
Ah, a very good question. It matters because when you connect a signal to scope, that signal must be referenced to the ground of the scope. This is true whether the signal is a display channel or an EXT sync input. If the signal itself is floating with respect to ground, you are going to have to connect the ground of the scope to whatever point in the circuit the signal is referenced form. For example, the 26-volt isolation transformer you spoke of has two wires coming out. If you want to connect the scope to one of those wires, then the ground of the scope has to be connected to the other wire. If that other wire was actually 200 volts above ground, then your scope (if it is not a grounded scope) will now have its chassis ground elevated to 200 volts above ground, so that if you touch it, and some part of you is grounded, you will be electrocuted. Or, if the scope is grounded, then connecting the ground of the scope to that 200 volt reference will short out that 200 volts, possibly destroying some circuitry, or at least blowing a fuse. On the other hand, if the output of the isolation transformer is truly floating, then it can be pushed around to any voltage you like (including ground) and it will not complain. You need to find out ahead of time which of these scenarios is the case and respond accordingly. It takes a thorough understanding of circuit board you are testing to answer this question. There are some empirical tests, like trying to gently force a voltage onto a point in the circuit that might be floating and seeing how much current that point draws from your "forcing". However it is much better if you just know what is going on without having to test it empirically.
TRUE , the secondary side is floating , so you can't use this as a reference because it's floating right?
Not necessarily. If it is truly floating, then it can be tied to ground without any problems. And then you can connect it to the scope. There are also battery operated scopes that are very well suited to scoping floating circuits, because the scope floats with the circuit.