What Most People Get Wrong
Most homeowners here assume a sensor that worked last month should still work this month, and when the opener starts reversing or refuses to close, they jump straight to replacing the opener board. On a lot of Downey houses - this city's housing mostly dates to the 1960s and 70s, with stock running from 1943 up through 2012 and a median build year of 1963 - the opener is often newer than the door and track, but the sensor brackets are usually bolted to the same original track hardware that's been there since the house was framed. Nobody touches those brackets during an opener swap unless the installer specifically checks them, so the misalignment problem outlives two or three openers. The sensors aren't failing electronically nearly as often as people think; they're just no longer looking at each other the way they were set up to. A sensor eye that's off by even a few degrees reads as 'blocked' and the opener refuses to run the motor, which looks exactly like a dead opener from the driveway.
The Problem
Garage slabs and the stud framing that tracks get fastened to move very slightly over decades, and on a house built in the 1960s that movement has had sixty-plus years to accumulate. It doesn't take an earthquake-grade shift, just the slow settling that any 60-year-old slab goes through. One bracket drifts a sixteenth of an inch lower than the other, and the infrared beam that used to run dead level now clips the edge of the receiving eye instead of the center. The opener sees that as an obstruction and won't let the door close, or it reverses the door partway down. Because this is gradual, most owners notice it as an intermittent problem for months before it becomes a daily one - the door closes fine on a cold morning when the track metal has contracted a hair, then refuses by afternoon.
What to Check
Start by looking at both sensor brackets where they bolt to the track - not the sensor housing itself, the bracket. On older track, that bolt and the slotted hole it sits in can be worn enough that the bracket rocks slightly when you nudge it by hand. If one eye has a steady light and the other blinks or stays dark, that's your misalignment, not a wiring fault. Wipe both lenses first; dust buildup reads the same as misalignment and gets blamed on the sensors constantly. If the brackets themselves are bent, rusted, or the mounting holes are stripped from age, realigning them is a stopgap - replacing the bracket is the actual fix, and that's a part we don't always have on the truck for older track styles, so a same-visit fix isn't guaranteed. We don't recommend rewiring a sensor pair as a first move; nine times out of ten the fix is mechanical, not electrical.
