Here's a little something I have discovered and wish to pass on as a way of thanking you guys for the endless gas and empty bank account that you have so generously given to me! Many pedals, especially those which use the square, circuit mounted power input sockets for their 9 volt power supplies (like Digitech and Tech 21) develop a problem where after using a power supply for any prolonged period of time won't then run off of batteries. I see many like these secondhand when listed on Ebay. The reason is that inside the power jack socket is a metal contact that is separated from seeing a battery as a power source the moment a 9 volt DC jack is inserted in it. When the power jack is removed this contact is supposed to spring back and separate to allow a battery's power through. Because this metal 'spring action' is a very fragile mechanism (no doubt due to the use of cheaper materials these days) after having being held in the open position by a power plug, it will often stay stuck in the power in 'position' and therefore won't 'see' a battery power source. I have often found that you can separate this tiny metal contact tag (which contacts with the barrel part of a DC power in jack) using a fine needle to prise it apart again before it is necessary to replace the socket entirely. Peace, Rob.