If I use a vom and go to the plugs at the sensors and remove the plugs and put the probes to the wires on the plug connectors what voltage should be there?
If one or both sensors are blinking, the sensors are misaligned.
If one of the sensors is out, the door sensors typically need to be replaced.
If both sensors are out, the problem is typically a bad logic board or bad sensor wiring. You can test the wires/ sensors with an ohm meter and terminals. You can remove the sensor wires from the terminals on the logic board and check for voltage across terminals 2 and 3 (black and white) on the logic board. If you have 4-5v you will need to replace the sensors. If you don't have 4-5v between terminals 2 and 3 and the opener is plugged in, the logic board is bad. You can also test the wiring at the sensors to verify that you have 4-5v. This will tell you if the wiring is bad or shorted.