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Solution: Using the auto set feature on the FNIRSI 1013D oscilloscope without a voltage across the probe leads (i.e., shorting gnd lead to signal on the probe) will brick the scope.

I was recently playing with an Arduino Nano and testing someone's code with a scope probe (FNIRSI 1013D). The scope probe's ground was set to ground on the Nano. I was sweeping the signal lead across analog pins looking for a signal, accidentally hit the ground pin without thinking about it, shorted the two leads and bricked the scope.

How do I sweep pins to locate a signal without damaging my scope? My first thought was that there must be some sort of impedance between the two leads, but I don't think that's right. I believe the reference lead should have some sort of DC offset, like -1 V or 6 V if the operating range is between 0 and 5 V.

But this confuses me slightly more. I can see with digital PWM signals there is some sort of offset (low condition is never actually ground due to hysteresis), but AC signals frequently cross 0 V. And if the probes are not connected to anything, there is a high-impedance condition. So what is actually happening?

Edit: This is the schematic. I had the ground lead on the ground pin below D2. The other lead was sweeping across the left [moving from terminal to terminal while I was looking at the display]. When it hit RST or GND below the +5 V pin is when the scope started dying. Was it actually GND or was it RST? I don't know, it happened in a couple seconds. I'm fairly sure it was ground, and the scope made a clicking sound in its autorange mode when it scales the signal to display, and subsequently died.

Arduino Nano Pinout

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  • \$\begingroup\$ Well, for one don't literally sweep your probe. But touching two probes together, in and of itself, should not be an issue. You probably need to provide a schematic of your circuit, what you were clipped to, and what you were sweeping. \$\endgroup\$
    – DKNguyen
    Jun 26, 2023 at 2:43
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    \$\begingroup\$ diomed - Hi, On Stack Exchange: (a) We don't put "solved" or similar in question titles. Accepting an answer is effectively indicating that a question has been solved. (b) We don't edit questions to put the answer in the question. Please write your own answer (or, if someone else provided the solution then ask them to write an answer) and then you can áccept the answer which is your choice of the "best" solution. || Please see here and here. Thanks. \$\endgroup\$
    – SamGibson
    Jun 26, 2023 at 4:36
  • \$\begingroup\$ Hypothesis: GND on this 'scope differs from GND on a line-connected lab 'scope. This 'scope has a puny AC supply to charge its battery, so its probe ground clip doesn't connect to earth. This fact may be the "brick that broke". Exactly how it happened is mysterious, but I can imagine a transient discharge caused an internal 'scope over-voltage - enough to cause damage. It might help to describe its current state: completely dead? If it is powered from a different 5V supply, does it start? \$\endgroup\$
    – glen_geek
    Jun 26, 2023 at 13:04
  • \$\begingroup\$ @glen_geek When I use either the provided charger or my laptop's USB-C charger, the red LED indicating charging status is off. I suspect something is wrong with the power system. I took the scope apart; there is shielding on one side of the board, which I desoldered and removed. Under the shielding are six HFD signal relays. These components make clicking sounds when the scope is powering on and autoranging. I have not yet looked into it more. \$\endgroup\$
    – diomed
    Jun 30, 2023 at 2:12

1 Answer 1

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So obviously dragging the probe tip across the pins poses a risk of shorting pins together which could damage the device under test, so it's better to avoid doing that. But I've done this a few times myself on low-cost hardware where I just wanted to quickly verify I saw the output on one of the pins so I can understand why you did it.

However, nothing you've described here provides an answer for why the scope died. I'm slightly confused about what you mean by "impedance between the probes" and the "DC Offset" of the probes. Most o-scope probes have impedances in the megaohm range and there shouldn't be any large dangerous currents that could flow in them. The only thing I would expect to get damaged by what you did is the Arduino, not the o-scope. Without more information on the exact setup, I can't think of a reason why the o-scope died. This setup should not have damaged it.

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  • \$\begingroup\$ Don't worry, I was not shorting the pins. The Nano was in a breadboard, my attention was on the scope display, I was moving the probe across the respective terminals of the pins. \$\endgroup\$
    – diomed
    Jun 26, 2023 at 3:27
  • \$\begingroup\$ "Impedance between the probes" and "DC offset" is operating under the assumption that there needs to be some kind of potential difference between probes. Sorry, I'm new to electronics and I don't have experience with oscilloscopes. \$\endgroup\$
    – diomed
    Jun 26, 2023 at 3:28
  • \$\begingroup\$ If theoretically I should be able to short the probes without issue then I think this particular scope model (FNIRSI 1013D) might have just autoranged itself to death. \$\endgroup\$
    – diomed
    Jun 26, 2023 at 3:29
  • \$\begingroup\$ So one thing to clarify, when you say probes, an oscope probe typically has two parts. A ground clip for setting the "0 V" level, and a signal probe that actually measures against the ground clip reference level. Are you calling these two parts, two probes? The two parts make up one probe. See an image here for what I'm talking about (m.media-amazon.com/images/I/51q7e44-z9L.jpg). So the signal you see on the oscope will be the voltage difference made by the device. Good oscope probes shouldn't interfere with the circuit. You can pretty much always touch basic oscope probes together. \$\endgroup\$
    – cEEa
    Jun 26, 2023 at 3:41
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    \$\begingroup\$ I'm going to give two answers based on how you might be naming things. Answer is the same though, no (in most basic cases). First case: shorting the probe ground lead to the probe signal lead will cause no harm. Second case: Having a ground pin on the device and a signal pin on the device. Shorting these pins through the metal of the oscope probe would cause no damage to the probe unless there was a really high current that melted things or something. This could damage the device you're probing though. What is the model of the probe that you're using with the oscope? \$\endgroup\$
    – cEEa
    Jun 26, 2023 at 3:53

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