"Arcing" between Oscilloscope and Stereo System

[rentner]

I wanted to hook up my oscilloscope to the stereo system hooked up to my computer.

The Stereo System or amplifier is not grounded, but the Audio Input is grounded over the PC Soundcard. The oscilloscope of course is grounded aswell. I did measure the Voltage difference between the stereo amplifier output and the oscilloscope ground and input pins in all thinkable combinations and did not get any difference other than 5mV over the 2 Ground points, which can happen in a ground loop. But why did it arc or short, when I hooked up the Vin of the oscilloscope to the Vout of the amplifier? How can that be without noticeable potential differences?

[con-f-use]

After you measured, you might have changed cloths or rubbed on something -> electro static discharge. Did anything break?

[rentner]

It is working all fine. I don't know why, but after switching the pins, no short circuit happened again, so even I don't know why, it is working now. No Idea, what the problem was. Just 1 combination of input shorts out everything - and that without music playing so without any potential.

[Galaxyrise]

I presume you measured the dc potential; I suppose there could have been an AC potential that looked like near 0 to a DC voltmeter.  But since the probe tip should be high impedance to everything else, I find it more likely that you touched two things together that you didn't mean to touch.

[Bryan]

http://youtu.be/xaELqAo4kkQ

[rentner]

Bryan: That Video does not explain this. I am well aware of it! If no music is applied, I have 0V at the Output. And GND is 0V. Oscilloscope GND is 0V and Oscilloscope GND is high impedance. So none of all compinations CAN actually cause a short. 3 Cables have 0V and one is so high impedance, that even 500V would not let it spark.


But that issue is fixed anyway.