Does your V3 intermittently lose power when it's moved, you jiggle the cable/connector, or just plain won't power up?
I had the same problem and found the solution on the Oade board by someone who'd spoken with Grace about it.
If you look at the female power plug built into the V3, you'll see there's a pair of pins in the center of the plug. Over time, these two pins get pushed together a bit, and therefore don't have solid/consistent contact with the inserted power plug.
To resolve the problem, very gently use a small glasses-type screwdriver or some such to pry the 2 pins apart just a bit. It doesn't take much. This should provide sufficient contact and reliable power.
(Don't snap the pins! If you do, you're hosed. Don't wanna scare you, it actually isn't very easy to break 'em as long as you're careful, just trying to emphasize - be careful.)