The board works when connected to via USB and I can even upload code. But when I connect external 9V supply, it does not work. The LED ON indicator is not working. I checked the adapter to make sure I’m getting 9V and it seems fine. The leads of the barrell connector are 9V as well. Is it a problem with the voltage regulator? How can I check?
Never mind, I figured it out. The AC/DC adapter’s barrell connector had the reverse polarity, i.e., Positive on the sleeve and negative inside. Arduino expects it the other way around. Was able to flip the wires and make it work.
Yeah, I hate it when that happens! Not a bad idea to grab a DMM and see what the polarity is on the power supply and double-checking the polarity on Arduino barrel jack connectors which should be center postitive.
There are also dimension checks. Barrel jack connectors for Arduino products should be 5.5x2.1mm as far as I know.
Glad the issue and solution were simple. cheers for now.