This caused ,me some headaches so I'd like to share with you.
The instruction for the Brain Jr states that is doesn't matter how you connect faders to the analog input as long as the wiper is on the signal pin.
Well it does actually matter if the faders are mounted on a grounded metal plate as is the case with my setup. Everytime I screwed the panel down to the rest of the casing (which was grounded) the analog channels went completely crazy. After some measurement I found out that the metal of de faders where actually connected to the +connector on the Brain Jr. Breakout. Effectively causing a short between + and ground...
The easiest way for me to solve this was swapping the + and - wires on the breakout board and flipping the inputs in the configuration...
So remember: The part of the fader which connects to the outercasing of that fader should go to the - pin on the Brain Jr.
Hoped to help prevent some strange problems to some ;-)