Garage door opener

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.
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I doubt the circuit board is bad, since it is protected by the opener housing. Is it possible the wires were jostled so that one or more worked loose?
All voltages from the circuit board to the sensors will be in DC, less than 20 volts.
Any lightning strikes or power surges in your are lately? My opener experienced the same symptoms due to a lighning strike last summer.
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Smack your kid in the side of the head with the same broom. That should either fix the problem, or teach the kid a lesson.
Steve
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Do you have "electric eye" sensors on each side of the door opening (to prevent closing when obstructed)? Sound like they have gotten out of alignment. Clue is that door will work if you hold button down the whole time...and that you're getting blinking light on unit...that usually a self-diagnostic that sensors cant "see" each other. Check carefully. Still smack kid with broom handle for good measure.

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