I would do a search for the threads dealing with a very similar problem with the DD-3, they may contain good pointers. Firstly check physical connections inside the pedal - look for loose/broken wires, check components are not touching (shorting) on the bottom case panel, clean the switch with contact cleaner, try manipulating the cable ends in the jacks to see if any effect comes through and also check the pedal is receiving sufficient power (try a new battery or different adaptor). If still no luck then you would need to start looking at the components themselves - again the DD-3 threads give tips on where faults can occur and what components may need testing and replacing.