Mr +5v meets Mr Gnd

I shorted 5v and Gnd on my arduino nano while it was running on USB. Highlights the danger of poking around with a voltmeter. The chip wont power up now and Im guessing somthing is fried. Does anyone know what component is most likely to have taken the damage? Im thinking its possibly the USB chip.


I would think the most likely thing is the fuse in the computer or USB hub protecting the USB power line. Check (carefully) if there is 5 volts on the +5 volt line. If not, try connecting to another USB connector on your computer.

I was hoping that, the USB seems fine unfortunately and the Nano won't work on any other USB port either.

look at the big surface mount diode on the board, high currents can cause it to crack in half literally.

i can almost guarantee its not the atmega, as no current would have passed through the chip itself.

oh whoops i forgot you had a nano: the diode is on the bottom side between the yellow capacitors and the power LED. see if that is intact.

A short should bypass power to the chips, so they should be fine. Check to make sure that nothing failed short (you should have no continuity between 5V and ground) before doing anything else, though.

The diode is the most likely failure point, but the Nano also runs power through a few traces that aren't huge, so I suppose there's a remote possibility that one of them failed, particularly around the USB connector. I would use a continuity tester on the board (with no power connected) to locate the failure. If it is the diode, external power should still work, and you should be able to solder a jumper across the diode to get usb power working again. Many boards don't even have a power selection diode.

Thanks guys, shorting the diode did the job.

Im reading 0.5 megaohms resistance between +5v and analogue inputs. Is this normal?

Mine reads closer to 10 (DIP package), I wouldn't worry about it.

Glad to hear it's working. I just hope you've learned your lesson, you won't have such an obvious failure point if it happens again.

Thanks guys, shorting the diode did the job.

You have just removed any protection you had. It would be better to replace the diode if you have SMD soldering skills.

Mr +5v meets Mr Gnd

Those two don't play well together without something between them, do they!


They certainly dont :). Managed to solder a piece of wire across the diode last night and it started up right away. Thanks for the help I would have thrown it away otherwise.