I have a mega 2560 and ramps 1.4 for a 3d printer. I can control the printer and do everything with it however I can't power the Arduino with out the USB and with the 12v power supply like I used to. Everything works perfectly when the arduino USB is plugged in.
When I use only the 12v supply I get a slightly backlit screen and nothing else. I have done a bit if researching and have checked both D1 and D2 diodes these still both seem to work as they should. I have tried to understand as much as I can and electronics is not my strongest point so the schematic is some what foreign looking.
So I have removed the Ramps board and now I only have the mega 2560 in question
I have connected +12v to the 'VIN' pin and and ground to GND.
I have measured across the 5v regulator and the input pin reads at MINUS 3v. The output pin is reading PLUS 8v. I'm hoping to replace the regulator but the fact that the input is reading -3v makes me think something before the regulator is throwing this??
Thanks in advance for any input, Wes.