| Electronics > Beginners |
| I keep ruining circuits with oscilloscope |
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| JxR:
Now, I'm not saying this is your problem, but: You need to be careful with this power supply. It has (or at-least used to have) a design flaw, where it would supply a negative voltage when the output is turned off. I killed a couple microcontrollers with it until I fixed the problem. You can test this with a multi-meter to be sure. The repair requires removing one of the transistors and adding some extra resistors. It is discussed in this thread: https://www.eevblog.com/forum/testgear/tekpower-tp3016m-power-supply-output-funkiness/ (same power supply, different brand) Honestly, I probably haven't used mine in over a year, but the outputs are certainly isolated from mains, and after the repair it is a decent little unit for the portability factor. Also, if you discover that you have this same problem I would consider adding a switch to physically turn the powersupply off while you already have it open. It always bothered me that the powersupply remains on whenever its plugged in. |
| Jeroen3:
Above power supply is isolated, see the double square symbol on the back, but it is not linear. (Maximum float voltage is on the back I believe.) This means it is a switching power supply, and it has a high leakage current. It also has a two capacitances: - Capacitance from the Y capacitor, because it is switching. - System capacitance that must discharge when you attach ground to it. This is what kills your board, as it is similar to a severe ESD burst. The second one will also happen to any people who have "floated" their scope and attach the ground while power is already on. A linear power supply with a foiled isolation transformer does not have the first problem, and the second one is negligible. |
| David Hess:
--- Quote from: cabalist on May 28, 2019, 05:14:20 am --- --- Quote ---Combine two oscilloscope channels using add and inverter mode (or subtraction) and use them as a differential probe with the ground leads connected together and not to anything else. --- End quote --- @David Hess I never would have though of that. Very interesting. Thank you. --- End quote --- I have occasionally done this is the field when I do not know if "ground" on the device under test is the same as the ground my oscilloscope is plugged into. Watching an oscilloscope ground lead turn white hot and melt once was enough. |
| Psi:
Your mileage may vary using the two probe differential mode trick. It works better on some scopes than others. With some scopes it turns into a noisy mess very quickly. |
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