Our voltage regulator on our Arduino Mega2560 is smoking, and we don't have any idea why. Can someone please help?

So we are designing a 3D bioprinter using an Arduino Mega2560 along with a RAMPS board to power our motors and LCD screen. We are using open source software for the RepRap printer Marlin (http://reprap.org/wiki/Marlin). Our RAMPS board is powered by an external power supply unit. When we have only our motors plugged in, we have some control over them, but when we plug the LCD screen in, the voltage regulator starts to smoke.

Its surprising that the LCD is enough to push the regulator over the edge. Have you tried the LCD on its own, with the RAMPS board disconnected from the Arduino ?

Well that answer is simple it is working hard.

If you check the data sheet on the voltage regulator of Arduino it is a lot less current than a LM7805 take a CJ78L05, it is only good for 100 ma.

Then the additional hardware is causing a major power draw on the regulator. Your trying to pull more power from it than it can provide or you just need to add a heatsync.