Uno external power supply problem

Hi, everyone. I'm a newbie (though I've been following these forums for some time).

I've never had to run the Arduino uno off an external power supply until now. So I connected the + ve terminal of the battery to the 2.1 mm barrel plug's centre connection and - ve to the outside connection. Nothing happened. LED didn't light up, nothing seemed to be burning either.

Then I connected the + ve to Vin and - ve to Gnd. Still nothing.

It runs just fine on a USB connection even now. But external power supply hasn't powered it even once. I have checked the diode between the 2.1mm jack and Vin. It is also fine. The 5 V regulator seems fine (it also allows current in only one direction and doesn't allow it in the opposite direction), but I'm not too sure. Any guesses as to what is wrong and why this happened?

When you attach external power to the power connector and not plugged into USB, measure the voltage on the 5 volt header pin. What do you get?

oops …between Pin 1 and Pin 2 of the regulator (see attached), there isn’t supposed be any continuity, is there?

Will replacing this regulator do the trick or does something else needs to be replaced as well?


Pin 1 is GND pin 2 is o/p. Remove the power and USB cable. What are you measuring between these? If this is shorted, your USB would note work either.

I get around 5 V between pin 1 and pin 2, 2.5 V between pin2 and pin3, 7.6 V between pin1 and pin3.

Also, between pin 1 and pin 2 of 3.3 V regulator, I get 3.2 V, between pin2 and pin3--4.2 V, pin 1 and pin3--7.5 V

Are you measuring at these points?

Yes. 5 V and 3.3 V between outputs and Gnds.

The plastic of the board next to the heat sinks looks a little rough. But I’m not sure if it was there already. The heat sinks also looks a little oxidized around the edges.