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

Step 1: OPEN THE PROCESOR

just unscrew the back cover and be careful to put the five screws in a safe place

Step 2: GENTLY REMOVING THE FOOT SWITCHES PART

as this step says, gently remove the foot switch's pcb board and, with caution, remove the cable from the pins; it is not crucial, but it will be more comfortable to solder the contacts this way

Step 3: SOLDERING THE NEW SWITCHES

remove the defected switch and solder the new one. put everything back in order make sure the switches work before you close the processor. so... if the only problem you had was with the effect switch you're done. congratulations!

for the bank buttons move on to the next step

Step 4: CHANGING THE BANK/ EFFECT TYPE BUTTONS

these buttons are a little more time consuming to change, 'cause of the place where they are mounted, but it's no harder than the foot switches.

Step 5: GETTING TO THE PCB

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.

Step 6: GETTING IT FINISHED

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.