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Problem when adding the Oscilloscope probe to my circuit output

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NHSA:
Hi,

I was not sure if I should post this poblem or not  :-//  but I have not found a solution after 3 days analyzing it   :-[

Attached circuit image with marked oscilloscope probe position.

My positive / negative voltage solution using two zener diodes 1N4732A and a 100 Ohm resitor works fine. Just 15mA current consumption. Sorry the schematics has not been changed to the Zener Diode / Resistor power supply. Still depicts a battery powering or athe resistor voltage divider which is also not valis anymore. Need to change it.

When I do connect the oscilloscope probe which is connected to the oscilloscope I need to crank up the amplifier power nearly to the maximum on trim pot RV3 for Amplifier 1B because the 10LED bar does not show anything anymore. Disconnecting the oscilloscope probe I need to adjust down the trim pot RV3 50K value of Amplifier 1B.

When I just connect the oscilloscope probe (NOT connected to the oscilloscope) it does not happen e.g. the trim pot RV3 50K of amplifier 1B does not need to be cranked up.

I guess something is pulling the voltage potential of the output down to ground ¿?

I tried simulating a probe circuit at the output but no I had no luck getting the same result.

The power brick is a 2 pole main connector. It has NO ground to my mains while the oscilloscope does have it.

Thanks in advance for any tip.

regards Rainer

David Hess:
If the power supply is not floating, then attaching the oscilloscope probe ground to ground in the circuit likely shorts negative to ground.

NHSA:

--- Quote from: David Hess on August 01, 2021, 08:54:47 am ---If the power supply is not floating, then attaching the oscilloscope probe ground to ground in the circuit likely shorts negative to ground.

--- End quote ---

Hi David,

Will check what floating power supply means. Thanks.

Need to test it again with batteries if it behaves same ... Do not remember ...

Thanks Rainer

tunk:
Is this any help: https://youtu.be/xaELqAo4kkQ

NHSA:

--- Quote from: tunk on August 01, 2021, 07:53:48 pm ---Is this any help: https://youtu.be/xaELqAo4kkQ

--- End quote ---

Hi tunk,

Thanks for the link and yes I already saw that video but that is not my problem.

My oscilloscope probe connection has been always correct and on points with nearly no current flow at all.

 :-+

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