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My Arduino Uno (r3) board seems to be broken. It can still be powered over USB, and can store/run code properly, but the DC power in system appears to be crippled. I'm not entirely sure what happened, but I was most likely being careless with the power in and the vin pin. I'm not sure what component(s) are broken, but when I plug in 12v into the barrel connector, the uno doesn't power on. I can read about 0.6 volts from the 5 volt pin, and at some other locations on the board. Besides the 0.6, the only other voltage I read is the 12 volt, although it is slightly lower than the power supply, which outputs about 12.2 volts. How can I go about fixing this? Or is it even worth it?

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    Most certainly the voltage regulator is broken. Maybe you shorted the 5V pin intermediately or you tried to draw too much current from it. Do you have a specific question? – chrisl Nov 10 '18 at 8:28
  • What is the voltage of the vin pin? If it is near 0v, then the diode is blown, if it is near 12v then the voltage regulator is broken. A broken voltage regulator can leak current of have a shortcut, if you remove a broken voltage regulator then you can use the board with usb power. – Jot Nov 10 '18 at 13:21
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As you have noticed, measuring voltages is the first step. Here's some voltages for you and what they mean if they aren't there. These are all assuming precisely 12V in through the barrel jack. They are in order of "priority" - start at the top and work down, the first one that fails is your culpret (i.e., the barrel jack feeds VIN through the diode, VIN feeds 5V through the 5V regulator, and 5V feeds 3.3V through the 3.3V regulator).

  • Roughly 11.4V on VIN - if it's not there the input protection diode has blown
  • 5V on the 5V pin - if it's not there the 5V regulator has blown
  • 3.3V on the 3.3V pin - if it's not there the 3.3V regulator has blown

Fixing it may be as simple as replacing the faulty component identified above - although they are all surface mount and some are more tricky to replace than others. That said, if it is (as it sounds) the 5V regulator that has gone, that is one of the larger components (SOT-223) so should be eaiser to replace. Also it's dirt cheap - I get them for a few cents each in bulk.

  • It would appear to be the 5v regulator, thank you! This was super helpful – John Freeland Nov 10 '18 at 19:45

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