Motherboard is no longer powering up.

We have about 2k+ of this model. I am starting to see lots of them fail due to power failure at the charging post. I have fixed this by replacing the motherboard. I hope someone has a better fix for this. Like maybe a bad solder job. Have not been able to identify the problem other than replacing the motherboard. The device is now 18 months old and only had a 12 month warranty. Being a school district, people cringe when I ask them to spend money. Please Help.