if you are having problems switching through presets or banks , this should probably mean that the micro switches have worn out. this instructable will guide you through a few steps on how to change them.
all you need is :
a soldering iron
a few micro switches
a screw driver
first, you have to unscrew the jack inputs and output , then the circuit board can be removed slowly( it's not screwed to the chases )
one you get to the actual circuitry, remove the two screws and turn the cover and remove the knob buttons by just pulling them out. remove the nut and then you can remove the defected buttons and replace them.
screw all the circuitry back on, connect the cables to the pins, check once more for the buttons to work , close the back cover and you're ready to rock with your favorite multi effect processor that responds like the first time you turned it on.
please excuse me if i made any expression mistakes and if i'm unclear in any of the steps; it's my first instructable.