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dsox3024 / msox3024 triggering

Question asked by PhilTaylor on Dec 13, 2011
Latest reply on Feb 19, 2012 by p7146
I've had a number of difficulties getting my scope (msox3024a) to trigger correctly, and sometimes at all.

In an attempt to go back to a baseline I could trust, I have connected my probe to the probe comp output.

After restoring factory default settings, and updating my firmware I see the same trouble. 

The probe/comp output is a composite of the base signal (1kHz  @ 2.5Vpp) and an am-modulated type waveform at the two frequencies:

95 MHz    carrier freq.   (100mV RMS these two combined)
2.2MHz    modn freq.

The problem does not seem to be the probe/comp generator, as the same AM signal is present on the  probe/comp ground lug, as well as the BNC ground rings on the other channels.  This signal is attenuated approx 3dB when connecting both the probe tip and ground spring to the Ground Lug (see photo).  The size of this loop seems inconsistent with these frequencies being radiated into the probe.

Image

This AM signal is at a high enough level that it swamps even the high/low slewing transistions of the base square wave.  Therefore, the scope will not trigger.

The problem is two fold.  There is garbage running around on the grounds of the scope (bnc shields, probe shields, and test point "ground").  Then additionally the scope cannot window or average the data in its trigger setting to produce a stable (or any, sometimes) waveform on the screen.

I have read all of the other discussions about the noise on the DSOX3024 ... I am simply not convinced that there is not something wrong with my scope, or the scope in general.  I would welcome any direction in sorting out this fundamental usability issue.  

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