Sat oscilloscope probe down and it hit a point causing a short - Page 1
Forum section: electronics / beginners

author: dewcansam
author_rank: Newbie
timestamp: May 31, 2024, 02:53:13 am
content: I just got a real oscilloscope and was testing it out on a laptop that is not getting power somewhere. Even though I still have no idea what I am doing, I felt like I was learning something. I was finished and sat down the probe. It then jumped (flopped) from where I sat the probe down and it hit a point on the pc board causing aspark. Fortunately it was very brief. And I know that the voltage at that point was 19v. I tried to test the scope after that and it seemed okay. So my questions are. What would happen to the scope if it does cause a short ? Will it mess up the probe ? Will it mess up the scope itself ?Well, crud, this took a turn for the worse. I am beginning to suffer from dementia and I can loose my complete thought pattern. So I can't complete my thought or series of questions. So if anyone can provide any extra info on oscilloscope probes shorting would be helpful.

author: SteveThackery
author_rank: Super Contributor
timestamp: May 31, 2024, 09:12:58 am
content: I don't think you will have done any harm to the oscilloscope or probe if the highest voltage involved is 19V. The probe must have bridged two points on the circuit board to cause a spark. You can't get a spark just by touching a single point on the circuit, because the probe has a very high impedance.Such a accident is more likely to damage the circuit under test than the probe or 'scope.

author: Ian.M
author_rank: Super Contributor
timestamp: May 31, 2024, 09:21:15 am
content: Without the hook tip installed, oscilloscope probes generally have an exposed ground ring round the tip, and that is probably what shorted your board. New probes generally come with a plastic cover for the ground ring you can fit as required. However its generally bad practice to put the probe down on or too close to the circuit board when not using it so get in the habit of unclipping the ground lead from the PCB and setting the probe down somewhere safe!

author: pcprogrammer
author_rank: Super Contributor
timestamp: May 31, 2024, 09:24:43 am
content: Check the tip of the probe to see if there is any damage from the spark. Might have caused some oxidation or blacking that needs to be cleaned. The scope itself can withstand these low voltages even in x1 setting of the probe, but be careful in situations with higher voltages.Also check on the PCB what damage is caused. Maybe it was on a capacitor and it being briefly it might not have done any harm. 19V on a laptop sounds like very near the input of the adapter in the power supply section, and only shorted to ground.

author: tggzzz
author_rank: Super Contributor
timestamp: May 31, 2024, 09:31:55 am
content: Quote from: dewcansam on May 31, 2024, 02:53:13 amIt will depend on which part of the probe touched the circuit (tip or shield), where the current flowed (e.g. along the shield, or just within a probe clip), and the magnitude of the current.If the probe shield touched 19V and the current was conducted along the shield to the scope's case and protective mains earth, then I suspect the scope was not damaged but a high current might have damaged the probe's shield. Visually inspect it carefully.Do NOT under any circumstances remove/disconnect a scope's earth wire. Such "floating a scope" can be literally LETHAL. See references below for examples.QuoteSee the safety and praxis section ofhttps://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/and the references about the correct types of probe to use.Sadly as we age we do become less capable; examples include but are not limited to failing eyesight and shaking hands. It is necessary that we adapt out actionsand objectives/aspirationsas we grow older.

author: jh15
author_rank: Frequent Contributor
timestamp: May 31, 2024, 02:35:52 pm
content: EEVblog #279 "How not to blow up your oscilloscope" refers to the grounded scope issue.

author: dewcansam
author_rank: Newbie
timestamp: June 01, 2024, 06:56:14 am
content: I gave the scope a very close once over and yes, there is a very small mark on the collar. So it was the collar that hit the board. I then put each probe, singularly, through the compensation test, then put the probe on the other channel. And everything tested good. So I just have to do a better job of where I am placing things.I had watched that episode of "How not to blow up your oscilloscope" once before. But I think it was only on in the background. So good recommendation to watch it again.Thank you all for your suggestions.