My 3D printer is down for an extended break. While fixing the connector problem, I accidentally plugged the X sensor in one location over to the right, shorting 5V to ground on my Arduino Mega that controls the printer.
How did this happen?
I was fixing the connector issue mentioned in a previous post and was testing it. I was just inserting the last connectors for the X, Y and Z end stop connectors.
I was in a hurry to do something upstairs, I just pushed them into their location, I never turned it on.

Next day I turned on the printer and noticed the LCD did not come on. I quickly turned it off and went over to the control board and could instantly smell the distinctive smell of burning semiconductor.

I remembered the last thing I did and, in better light, I could see that I had shifted the connector over one location. I had caused a short circuit. To fix it I removed the regulator from another Arduino board that I had. (I will order a new regulator when I get a chance). Soldered in the part.
It now appears to be working again.