I've just received my Uno today and already I think I may have broken it :(

I was able to connect to usb and upload a sketch (the blink). However, I then tried to connect a circuit to do the Hello World LCD example. After trying this a few times, I noticed the LCD chip get very hot...and I had mis-wired it. In any case, after a few more tries, the USB connection to my Arduino UNO stopped working.

I tried swapping the cable, connecting it to another mac and to a windows with no luck. I'm worried I may have shorted the USB bus chip when trying Hello World.

I also tried connecting a 12V DC power supply.

I still get the green power light and the amber L light... Did I break my Uno? How do I troubleshoot this one? thanks

  • What do you mean that it "has stopped working?" Any errors? Right COM/board selected? Any luck with no LCD? Commented Jul 19, 2014 at 3:42
  • Basically the serial USB didn't show in the list of ports and also it doesn't show in the mac system profiler...no luck with the lcd
    – hagope
    Commented Jul 19, 2014 at 3:59
  • Try reflashing the firmware on the atmega8u2. You might be able to do this using dfu, if the bootloader on it wasn't corrupted (too).
    – Gerben
    Commented Jul 19, 2014 at 14:52
  • Very similar disscussion: arduino.stackexchange.com/q/129/37 Commented Aug 28, 2014 at 22:35

2 Answers 2


When the LCD pulled enough current to overheat, the Arduino's power supply (which I gather was the Uno's USB interface, at the time) was probably stressed to the point of failure. One fortunate result is that the Arduino took the hit instead of the computer's USB port that was supplying it. It's not clear which part was involved but here's a discussion on another forum concerning a similar failure and replacing the ATMegaxU2 which does USB-interface duty on the Uno (x = 8, if it's a rev 2 Uno, x = 16, if rev 3). It may be possible to replace the failed chip - regulator or USB interface (though with LEDs working, it's probably not the regulator). Otherwise, you can probably still program it with an ISP (In System Programmer). But the easiest way to do that is probably involves another Uno.

  • Replacing a QFN is no easy feat. Drawing to much current however shouldn't break the atmegaXu2. The u2 is only connected to the atmega328 via TX and RX, and those connections have a resistor. My suggestion would be to try reflashing the firmware on the atmegaXu2, and maybe replacing the atmega328 (which is could be broken due to excessive current through one of the IO pins).
    – Gerben
    Commented Jul 19, 2014 at 14:50

You can try and buy the Arduino serial board, and connect it directly to the pins on the Arduino , see if this works, basicly override the Arduino's own interface, or if you have another Arduino you can try and "serial" connect them using the first Arduino as ISP.

Else it is like JRobert says, you could move the chip from another arduino burn it on that one and then put it back, using the second Arduino as a run only.

Last but not least, you may find a cheap broken Arduino board on some online auction site, where the chip is broken, then move the defect chip to your defect board, and the working chip to the working board, and throw the defect Arduino in the electronics recycling.

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