Electronics > Beginners
Is something wrong with my oscilloscope?
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sincspecv:
I just got my first ever oscilloscope, a HP 56400B, that is showing ~5.5v with or without a probe attached on ch 1. Ch 2 is also showing voltage, but not as high as ch 1. Is this a misconfiguration somewhere or is it a bigger issue. I've gone through every menu to try to find a setting that would fix this but have not found anything.
Psi:
Did you mean to say HP 54600B instead of 56400B ?

Are you aware that you can move the trace up and down with the vertical position knobs for each channel?
The 'ground' level is not fixed to the centerline

Sorry if you already know this, i'm just not sure where your skill level is at.


It shows a little marker on the right to indicate where the 'ground' position is for each trace.
See here


Brumby:
Like Psi said - if you are new to oscilloscopes, it could be that simple.

Look for "Vertical position" adjustment.
sincspecv:
Sorry, yes it is an HP 54600B. I am completely new to oscilloscopes other than watching a couple of "how to" videos. I have the position set at 0.0V for both channels and it is still showing voltage. Possibly worth noting is that on Ch1 the voltage drops to ~2V when I change to 5V/div and lower.

Here is an image of what's going on on Ch1:


And here is Ch2 (it's actually showing negative voltage):


Thank you for your help.
ledtester:

Some things to try out:

- Set the channel coupling to GND
- With the probe tip grounded (i.e. the ground clip attached to the probe tip) set the coupling to AC
- Same as above with the couple set to DC

All three should give the same trace - i.e. the same horizontal line. (Don't change the vertical position during these tests.)

Then put your probes on the scope's calibrating signal output and it will be interesting to see what you get with AC coupling vs DC coupling.

While you are at it you might as well adjust the compensation on your probes:





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