I've been having issues ever since attaching the Atomic Pi Breakout board.
My Pi will periodically power cycle, so often I was able to see the 5V line drop to 0 on a meter.
A clean 5V 1A PS is attached to the FDD Power connector.
Iv'e tried 2 different PIs (which worked with the small breakout board)
I've disconnected everything from the breakout board except power (UART, speakers, USB, etc) with the same results.
While I haven't checked current draw, I cannot believe it's over 1A. Nothing is smoking, no obvious shorts I can see on the Breakout Board.