I have a Craftsman 1/2HP garage door opener. All has been well for several years. My son smacked the opener with a broom (not very hard but seems to be when the problems began). The door would not shut after this. It would barely start and then blick 10 times. I messed around with the sensors and the door shut normally. The next day, late in the afternoon, the door stopped working again. This time there were no lights on the sensors. I've checked the wiring and all appears fine. I bought an inexpensive electrical tester but really don't know how to work it. When I place the sensors on screw 2 and 3 and ask for AC, nothing moves; when I put the dial on DC, the needle jumps. How do I know if the main box is sending voltage to the sensors? I've read earlier suggestions and believe that the logic board is probably bad in the unit but I need to verify its not the sensors before replacing parts.
Also, the yellow light on the back of the unit flashes. There doesn't seem to be a pattern to the flashing but it might be related. At the current time, the remotes won't work; the keypad won't work, only the direct wired button works if it is held in the entire time.
Many thanks.