I have been using the Mega for a couple projects here recently, mostly for the mutliple UARTs. We built a board controlling small LED arrays running off a second power supply (using transistors). Upon powering the logic of the unit and programming it with USB, everything worked beautifully. The external supply connected to the shield separately and drove the meatier current to the LEDs. However, when powering the device with two power supplies (one for logic, one for LEDs), the unit runs smoothly for around a minute and then begins to reset about every 3 seconds.
Again, when powering this with USB, it works great and there's no overcurrent notice happening.
But when logic has an external supply connected (through the standard Mega barrel plug), the board gets very hot and appears to be failing through the regulator.
Just a bit stumped by this. I've been looking over the board design eagle files, and everything seems on point. I've done this before with a standard Arduino without problem, so I'm curious as to what could be causing the issues (and if its a flaw I don't see in the Mega design).
I can send on an image of the schematic if necessary.