MarkT:
The on-board regulator has the board as its heatsink - it can probably take upto a watt or a little less - 3.5W is way beyond safe.Most regulators detect over-temperature and shutdown automatically, which is probably what you see.
Add an external regulator with enough heatsinking?
I had a external regulator with heat sink semi-ready.
but the problem now is that if I connect using the power jack, nothing lights up.
if i connect using USB, arduino starts and all works but regulator gets really really hot. (but it shouldnt, right? cause usb is giving 5V directly, not going through the regulator.
Mark any guess of what can i try?
thanks a lot