This broke on transit to Vanbrugh college for Woodstock 2009. The symptoms of the problem were that it didn't mix, the 7-segment LED digits at the top were at a fixed value and couldn't be changed, the mixing T-bar didn't do anything, various LEDs were always on or always off regardless what buttons you pressed.
It turned out to be because two of the ribbon cables inside it had become disconnected at one end. Reattaching them made it work fine. Note: Panasonic Max has a LOT of screws on the bottom!