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?