I have a [SIM900 GPRS/GSM Shield](http://linksprite.com/wiki/index.php5?title=SIM900_GPRS/GSM_Shield) and an Arduino Mega. Now for the past week I have been using USB as power to send and receive GPRS data with no issue. Today the SIM900 module is continually randomly turning off, not even turning of at specific stages of communication.

I thought this could be power related, so have external power (5V 5A UBEC) into the 5V pin of the Mega, which I believe should cover the voltage and current requirements of the SIM900 shield. However this has not solved the problem.

Any ideas on what could be causing the random shutdowns?

EDIT:
Is it safe for me to wire power up like this:

[![enter image description here](https://i.stack.imgur.com/sImrM.png)](https://i.stack.imgur.com/sImrM.png)