Author Topic: Trying to not blow up scope - Grounding questions  (Read 2324 times)

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Offline pigtwo

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Trying to not blow up scope - Grounding questions
« on: January 25, 2017, 06:20:36 pm »
Hello everyone,

I'm having a weird problem that I thought someone here might have some insight on.  I'm working on a board that takes +5v as an input and also has a usb connection(+5v usb power not used).   I was originally using my bench power supply to power the +5v.  I could have the usb plugged in, the +5v from the PSU, and scope probes connected to the board(with ground clips all connected to the ground on the board) and everything worked perfectly for many hours.

I then switch to a different +5v supply and things seemed to be fine at first.  The USB connection and +5v worked together fine but when I attempted to turn on my scope it wouldn't turn on and right when I pressed the power button I heard the USB disconnect on my computer.  The scope was connected to the board at this time.

I initially thought that the new +5v supply wasn't isolated and that was causing a problem but it is isolated and all my probe grounds were connected to ground.

I moved my scope to a different part of my house and and it would turn on fine.  I brought it back to the bench with everything else turned off but the scope wouldn't turn on.  I tried a different power cable and the scope would turn on.  But then when I turned the +5v and usb on the scope wouldn't turn on again.  This time I switched the port on the power strip the scope is plugged into and it would turn on again.  I then tried turning each part on individually to determine where the problem was but this time the problem never showed up.  Now everything seems fine and works properly. 

Maybe this is an issue with my power strip but I thought I would check here to see if I'm missing something. 

Also, I checked the original power cable and it seems to be fine.

Thank you!

Offline Kappes Buur

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Re: Trying to not blow up scope - Grounding questions
« Reply #1 on: January 25, 2017, 07:53:56 pm »
Your problem most likely is the USB connection.
In 99% of the cases the USB power is not isolated.

Offline danadak

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Love Cypress PSOC, ATTiny, Bit Slice, OpAmps, Oscilloscopes, and Analog Gurus like Pease, Miller, Widlar, Dobkin, obsessed with being an engineer

Offline pigtwo

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Re: Trying to not blow up scope - Grounding questions
« Reply #3 on: January 26, 2017, 04:01:16 pm »
@Kappes Buur
I do think that the USB is not isolated but as long as I only connect the scope probes to ground this shouldn't cause problems right? 


Thank you for the links, I'll look through them to see if I can find anything.

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