The video explains everything. https://www.youtube.com/watch?v=MVE3yV51MDg

I accidentally made a duplicate post

Quote
tim3716
The video explains everything. https://www.youtube.com/watch?v=MVE3yV51MDg

IS D1 installed on the Ramps board is it in correctly and is it ok D1 provides the voltage to the Arduino from the Ramps supply

Other than that it may well be the Voltage Regulator on the arduino they are known to be fragile.

Doug

How do I test if it is installed correctly?

Quote
tim3716
How do I test if it is installed correctly?

See

D1 is shown in the centre of the pic make sure yours is in the same orientation (Stripe at the pwr connector end and if so you can measure it's Resistance it should be Low one way and high when you reverse your test meter leads.

HTH

Doug

I just tested it and It seems to be working fine.

It´s just a guts feeling, but you might have screwed up the mega-board, when you unsoldered the barrel connector.
Check the area around the barrel for missing or misaligned SMD components.
-Olaf