I've received a number of these units for repair, and all of them have had the same problem to varying degrees. The PWR jack, which is a mini-USB connection, had broken loose from the PCB. I've managed to fix all that have come in, but a couple needed some jumpers on the PCB to the connector pins as the connector coming loose ripped traces off the board.
I decided that since I was installing my virgin WIU on my new layout power panel, maybe I should look at mine to see what it's condition was. So I opened it up and here's what I saw. Note all he indicated points are devoid of any solder, they're completely bare. While there is a spot of solder on the bottom of the two outboard pins, it seems obvious from all the failures that it's not sufficient to hold the connector in place, my suspicion is that it barely touches the shell pins. This explains why even minor strain on the power connector can result in the connector breaking free, and of course, the WIU doesn't work any longer!
The fix really isn't that complicated, and it's a lot easier on a virgin unit that hasn't had the connector pulled off the PCB yet! I just reinforce the mounting by soldering all the bare places on the connector shell.
This may not make the connector bulletproof, but it will sure go a long way toward keeping it from breaking free of the PCB and killing your WIU. Here's what mine looks like, it's ready to go back into the case and hopefully provide years of reliable service. 
