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Registered Member #1198
Joined: Sat Dec 29 2007, 05:39AM
Location: Seattle, WA
Posts: 21
I am having some problems with my o-scope and I don't know enough about troubleshooting them to fix the problem. When I turn it on I get a nice clean trace at 0V. However whenever I touch the probe to something conductive I get this gibberish wave:
I also get something similar when I connect the probe to the output of a NE555 running in astable mode when I should be seeing a square wave. What confuses me is the internal self test comes through just fine:
It doesn't matter if I have the scope set to measure AC or DC, the gibberish wave looks the same. I also see the same thing no matter where I use my scope (at my apartment or my parents house). I tried using a different NE555 and I got the same gibberish on the scope. Last time I played around with my scope (probably 3 years ago; it's been safely stored indoors since) I could see the output of a NE555 clearly.
Can anyone shed some light on what might be happening?
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
The problem lies in the grounding. The ground clip in your scope isn't connected to ground anymore.
The wave you pick up is the 60Hz noise emitted by everything connected to mains.
If you connect the ground for the 555 circuit to the case of the scope you could probably continue to use your probe, but really you need to repair/replace the probe.
Registered Member #1198
Joined: Sat Dec 29 2007, 05:39AM
Location: Seattle, WA
Posts: 21
I figured what I was seeing was 60Hz noise. I played with the ground clip and got it more firmly attached. Now when I connect it to the output of the NE555 and the grounding clip to the circuit ground I see a solid line at about 7V (I'm powering it with a 9V battery).
I'll try some different component values and see if that changes anything.
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Oscilloscope Trouble
