I bought this as best bang for buck. Unfortunately mine just suddenly stopped working. I didn't use it a lot in my recording. It sat unused for months. I decided to use it and plugged it in. There is no variation in effect or tone when any of the knobs are turned. I;m speculating but perhaps the photo cell or bulb burnt out. I'm now in search of a new vibe pedal.
Update: It works again! I decided to see if I could diagnose the problem. Unscrewed back and after jiggling the battery I noticed a pop when one of the battery contacts hit the case. pulled out battery and the photo cells lit up. Solution was to put some tape on the raised ribs bordering the battery compartment. naked battery contacts cannot touch case now. All is good and it works! Suggest all owners apply insulating tape to inside of the case in the battery compartment!