XYZ Mode on a TDS784C

[Tony_G]

Hi All,

I borrowed a TDS784D to work on my HP 8340B Signal Generator and I'm trying to get the XYZ mode to work but not having much success.

The 8340B puts out a Z-Axis signal that is +5V when there is no signal and should be blanking, 0V when there is signal and -5V when the sweep frequency is coincident with the marker. You can see all 3 of those features in this image (Ch3 is the 8340B Z-Axis in this case, Ch2 is an 8473C Crystal Detector and Ch1 is the 8340B Sweep Output):



However when I turn on XYZ mode it isn't either blanking or showing the increased intensity for the marker:



The manual refers to 5 divisions rather than volts so I've tried playing around with the vertical scaling for the channel (CH3 in this case) but that seems to have no impact.

Does XYZ mode actually modulate the intensity as per the manual or is this the best I get and I should go buy an old analog scope? The reason I borrowed this scope was that my other digital ones either don't do anything with the Z or simply do the blanking so I can't get the marker.

Any suggestions on what I may be doing wrong?

Thanks,

TonyG