Can anyone tell me what lead to connect probes to when testing audio phase between two balanced (from XLR) signals in XY mode? Is is hot or cold, or somehow both or one and ground? Sorry, just got my first o-scope, an ancient tektronics 475.
TEK 475 is a great scope, or it was back in the 70s. You can look at that balanced wave a couple of ways, but XY mode is used more to compare two independent signals. For example, you can tune a VCO to a reference oscillator by probing each signal with the two channels in XY mode. For a close look at a balanced wave, set the mode switch to either CHOP or ALT with probes connected to pins 2 and 3 (assuming pin 1 is ground). You should see identical waveforms 180 degrees out of phase. With both vertical amp channels set to the same ZERO reference, MODE switch set to ADD and channel 2 inverted, the true balanced voltage wave will be displayed. Go back to ALT or CHOP mode and both traces should be aligned on top of each other.
The delayed sweep mode of these scopes can be very useful for viewing events in digital circuits. That was some seriously innovative scope design work. Triggering on a particular event, you can highlight a window of time, say 10 milliseconds later, then magnify that window in the display to see a string of microsecond long pulses. Even more fun, use a word recognizer to generate a trigger pulse only when a certain word appears on a parallel buss, then use delayed sweep to get a magnified look at what happens any given time later.