Electronics > Repair
Weird USB oscilloscope ground issue?
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m k:
Different grounds can have different levels on purpose.

180mA can be an overcurrent protected short.
magic:

--- Quote from: wraper on June 23, 2024, 08:25:35 am ---To the level of what he'd seen it's not normal.

--- End quote ---
Fair enough, I measured my own computers and found only up to 10mV between USB port grounds and PSU chassis under full load, so 250mV may be a little excessive. I also have a few mV difference between the chassis and earth on a nearby mains socket, indicating that I already have ground loops sending DC through mains earth, maybe through the monitor.
Alex_Baker:
I have tested earth paths around my workbench, which is where I am using the scope. I have not tested the earth path of the actual outlets in the wall since that would need me to turn the power off, but other than that I have not found any problems.

Correct me if I am wrong, but I don't think this stray current issue actually poses any risk to me or my electronics, so I don't think it is worth chasing any more. If I had to guess, a mixture of long usb cables and a sub-optimal set of power strips feeding my PC and workbench make this seem much worse than it normally would be.
wraper:

--- Quote from: Alex_Baker on June 26, 2024, 03:49:02 pm ---I have tested earth paths around my workbench, which is where I am using the scope. I have not tested the earth path of the actual outlets in the wall since that would need me to turn the power off, but other than that I have not found any problems.

Correct me if I am wrong, but I don't think this stray current issue actually poses any risk to me or my electronics, so I don't think it is worth chasing any more. If I had to guess, a mixture of long usb cables and a sub-optimal set of power strips feeding my PC and workbench make this seem much worse than it normally would be.

--- End quote ---
You don't need to shut down the power to check the earth connection. Yes it poses safety risk as some devices my be working without proper protective earth connection.
Alex_Baker:

--- Quote from: wraper on June 26, 2024, 04:01:13 pm ---Yes it poses safety risk as some devices my be working without proper protective earth connection.

--- End quote ---
I have tested all the earthed devices in this room, I cant find anything wrong with any of them.
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