My Mega 2560 R3 was working fine up until yesterday, using a Wall Wart, a 12 volt car battery, and also from the USB connection (I wasn't using them all simultaneously though). I am using a Ramps 1.4 shield with it, and yesterday I was taking voltage readings from the end stop pins on the Ramps. Suddenly, my board went dead. There was no noise or smoke or anything, so I'm thinking possible ESD, although my meter is a good one and should be somewhat protected against doing that?
I've been troubleshooting the problem, and I have discovered that the 2560 does still work, and I can use the Ramps shield with a car battery to power my five stepper motors, and everything is working fine - if I have the Arduino plugged into a USB port on my computer at the same time. But nothing works if I just plug in a battery, or a wall wart - either through Vin or the power jack.
I've chased power through the Ramps shield and found that it supplies the 12 volts directly to the Arduino Mega 2560 through the pin labled Vin and that the 2560 is supposed to automatically detect the external source and switch over, and I presume, regulate the power to 5 volts on board. I've poured over the schematics (what I could find), but I can't figure out what components handle that job, or if they are peripheral and can be replaced. There is a chip near the power jack that looks like it could be a voltage regulator, but I can't read the numbers on it, and it is not labeled on the board.
I can operate my project using external power for the shield, and a USB connected to a computer if I have no choice, however the Ramps I have also has a SDram port, and I'd like to fix this so that I can have it all stand alone.
My questions to those who might help me are as follows:
1 - Does anybody know how to repair the Arduino based on what I've described, (yes I can do surface mount repairs)?
2 - If it can't be fixed, can I make a small external 5 volt regulator (LM7805 ?) that taps into the 12 volt line I'm using, and connect it directly to the USB 5 volt input - perhaps with a switch to disconnect it when I actually use a computer USB connection?