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Okay, so I was following this tutorial to control an RGB led strip with Arduino Uno R3: http://learn.adafruit.com/rgb-led-strips/usage

And the LED strip wasn't lighting, so I tried plugging the other end of the LED strip into ground. Then I realized I was using the wrong pin for ground, so I switched that and then the lights were working, but the Arduino began to overheat, and the black box next to the 12v power supply and IOREF pin became unsoldered before I had a chance to unplug the power supply. USB power works at the moment, but not 12V.

What exactly happened to cause this? Should I have not plugged in the other side of the strip into ground? What is the black box that fell off, and is there any way to solder it back on?

Edit: The part is shown here: https://www.dropbox.com/s/xu7fbycufhlq9fl/arduinopart.png?m=

enter image description here

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What exactly happened to cause this?

It seems you short-circuited the power supply to ground.

What is the black box that fell off

The item marked M7 is a surface mount diode. It is equivalent to the standard 1N4007 rectifier diode. I believe it is there to protect the board against the power being connected with the wrong polarity.

enter image description here Uno schematic

If that heated up and melted the solder, it is probably damaged. You could replace it with a new one.

However if that has been damaged, it is possible other parts on the board are also damaged. If you were drawing power from the Vin pin, the PCB tracks may have also overheated, but you may be lucky.

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  • \$\begingroup\$ See the edited post for the photo. \$\endgroup\$
    – aftrumpet
    Commented Nov 16, 2013 at 16:23
  • \$\begingroup\$ So would this be fixed by soldering on a normal diode, or does it have to be similar to the one that fell off? As far as I can see no other parts were damaged. \$\endgroup\$
    – aftrumpet
    Commented Nov 16, 2013 at 16:31
  • \$\begingroup\$ @aftrumpet: see revised answer. I would replace it with a brand-new but equivalent M7 diode. \$\endgroup\$
    – RedGrittyBrick
    Commented Nov 16, 2013 at 16:34
  • \$\begingroup\$ Also I uploaded the blink code via USB to test if the Arduino is still functional and the 13 LED blinked, so at least that portion is functional. \$\endgroup\$
    – aftrumpet
    Commented Nov 16, 2013 at 18:24
  • \$\begingroup\$ @aftrumpet if you connect 12v to the vin pin (and ground to ground) do you get power to the board? If so, the diode did its job. If not, the 5v power regulator also died. \$\endgroup\$
    – Passerby
    Commented Nov 17, 2013 at 7:06

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