No communication after plugging in power supply

I have a RAMPS 1.4 board and an Arduino Mega as part of a SmartRap kit that I have never got successfully working.

I can connect them up to my computer via USB I am able to communicate with the Arduino. I can read a temperature and correctly see the status of an endstop. I have removed all other components for debugging purposes.

If I then plug in the power supply (to the 5A connector) I can no longer communicate with the board. If I unplug and plug the USB back in I can no longer connect.

I've checked the power supply output is 12V with a multimeter.

I'm slightly confused by the D1 diode, I have one (I think from looking at the board) and my understanding is that powers the Arduino if the USB isn't plugged in. Is this a problem if I want to use the 12V external power supply and USB at the same time?

I'm concerned I may have damaged either board with some incorrect wiring at some point or have a faulty component. Any advice would be greatly appreciated.

I had the same issue and the seller of my Mega 2560 believed it to be the 16000 crystal placed close to the USB port on the Mega 2560 board.
They said they sometimes saw this if the crystal was too close to the pcb or if excessive solder was used. Mine was flush up against the PCB.
I redid he soldering job but had no change.

The L led on the Mega had a steady light, as did the PWM led. Seller said it meant (so they believe) that the main chip worked fine. The L led also blinked once when pressing reset, which indicates that the main chip Works, but the USB interface is dead.

Can your computer even see the Mega Card when connected to USB? My USB port stopped working completely.I tried 4 different computers, one of them an XP, with two different cables.

From what I have understood it is ok, as you pretty much have to, have both USB and Ramps power connected. The USB to control it (unless you have lcd) and the power inputs to Ramps are necessary for all the devices to function.

I have read about the D1, but I honestly don't understand it.

Edited 1 time(s). Last edit at 03/31/2015 03:55PM by dintid.

Quote
dintid
Can your computer even see the Mega Card when connected to USB?

Yeah it can and so far as I can tell I can program it normally. I guess this means the Arduino is okay. I'm thinking the issue must either be a dodgy power supply or something to with the RAMPS board (either incorrectly configured or faulty).

Edited 1 time(s). Last edit at 04/05/2015 02:52PM by richardjgreen.