AnsweredAssumed Answered

54642A 2-Chan 500 MHz oscilloscope problem

Question asked by tjw on Mar 11, 2008
Latest reply on Mar 27, 2008 by edgardog
Hi,
    I have recently acquired a 54642A oscilloscope which has 2 channels, 500MHz bandwidth and a 1 or 2 GS/s sampling rate.

I do not have the correct 10073C 500MHz or 10070C 100 MHz probes to use with the oscilloscope so I am using a no-brand probe at the moment.

With the CAL signal (~5V p-p, 2KHz) connected to channel 1 or 2 using either the no-brand probe or a piece of hookup wire (< 6" long) and the vertical scale set to between 5 V/div to 500 mV/div, the display looks fine and all measurements are ok.

The problem is that when the vertical scale is switched to 200 mV/div and lower the displayed waveform appears to saturate and the flat tops of the CAL square wave become triangular - imagine an extremely under-compensated square wave. The vertical position control allows an offset of +-20V to be set but this still does not allow enough offset to see the peaks of the waveform, even though it is only 5 v p-p. The ground reference position also changes.

I am expecting the CAL signal to just clip and not change shape and distort so severely. What are the chances of this problem being caused by me not using the correct probe ? Do I have a hardware fault with the scope ?

Note that similar results are seen using a function generator although sinusoidal waveforms are ok. For example a 5 V p-p 10 KHz sine wave displays on all vertical settings from 200 mV/div to 2 mV/div without any visible distortion - just clipping as expected.

Any insight into what is happening will be appreciated.  

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