I am thinking that it is a cold solder situation I come across this once in a while with electronic stuff for some reason it either shows up when you first plug it in or when the warranty is up. I don't know why a cold solder will work for so long before showing up. I know a guy that have a electronics repair show here in Kamloops along time ago the first thing they did was a drop test hold item up 1 foot above a 2 inch thick rubber mat and drop if it worked then it was usually a cold solder then they just had t find it my way takes a bit more time to diagnose but will not harm other components and you find the spot quicker.