Sears Garage Door Opener/ problem closing door

I have an older , Sears, chain operated garage door opener. Mechanically, the door is working fine, but I have a problem with the two safety sensors that beam a light across the bottom edge of the door, about 5 inches off the floor bottom.
The door will open fine, but will not close. I am 99% sure the problem is in the two sensors just described.
On one of the sensors, which I think is the sending unit, the little pilot led light is bright and pretty. However, on the other unit, which is marked the "Receptor" unit, the small led light is barely, barely, lit. It is getting voltage, as the led pilot light will very faintly light up when I apply the electrical wiring plug into it. I can also tell that when I line up the two sensors, and then place my hand across the beam of light, I can just barely detect that it faintly changes the intensity of the led pilot light.
My suspicion is that this "Receptor" unit has gone bad.
Two Questions please:
1. Am I on the right track ?
2. Can these sensors be bought at Lowe's or Home Depot ?
---------------
Any comments or input would be very much appreciated.
Thank you very much !!
James
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wrote:

How old... Model?

Interesting. At least on mine, the lamp's brightness is directly related to the transmitter's light that it receives. Are you sure that the lenses are clean on both units (no cobwebs, crud, or other stuff there) and that they are properly aligned.

There is no way without measuring the light output of the transmitting one to determine that.

Maybe. Does the door not even try to close? Or does it get part way down, then reverse?

I don't think so, but it is possible. I've seen some parts at both stores that I'd not have thought the'd have carried.

Check the light path, and make 100% certain that there is no dirt, dust or crud partially blocking the lenses on either end.
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thank you so much Peter. One thing you mentioned was to check the lens cover on the Sending unit........ I had only checked the Receiver. I will check the Sender tomorrow.
The door will start down, but after a bit it will reverse and go back up. It will open fine. I can force it down by pushing the wall switch and holding it until the door is fully closed.
I need to get the model number of the unit, and will post it. I do know that it is quite old............
Thanks again.
James
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wrote:

OK, this sounds exactly like the force seensor is tripping. This is a sensor that monitors the motor's current, when it sees a rise in current above an acceptable predetermined limit, it reverses the door thinking that the door is blocked. This is doen because it is possible to have a car in the doorway but because of the wheels holding it (the car) above the sensor light beam, the light won't be blocked.
If the light sensor is not working the door will not even start down on most models.

'quite old' is a broad range! What I call old, some people think of as relatively new. And I've seen stuff that was described as old, and I figured it was relatively new! See if you can find a date code on the label...

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Agreed. The fastest diagnosis for that is to uncouple the door and see how hard it is to opena nd close by hand.

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I would oil and lube parts.... The force sensor is doing its job. I noticed on many automatic doors the hardware gets gummed up, rusty, and parts and pieces do get loose. After a tightening, and spraying WD-40 or some type oil.....things do work more smooth. jloomis

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Ok, I did try the "free wheel" test, by releasing the latch and manually putting the door up and down. It goes up and down freely, with no binding etc
I tried to do the eye to eye matchup with the two sensors, but when I plug the receiver sensor in, the led on the transmitter goes out. This is not right........
if i just keep power to the transmitter, the led comes on.......... but when I power the receiver, the transmitter light stays off, no matter where i aim the receiver.... there is just no pilot light on the sending unit........
from this, I am suspecting more and more that I have bad sensors.....
what you guys think ??
James
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Does it have force limit adjustments? They would be trim pots behind small holes in the case.
Probably ought not say this but... you can remove the optical safety sensor from the circuit. If you do not have any small children or stupid pets then it's not really that big a deal. Mine is old enough it does not have those sensors. Alternatively you could bypass it to see if that fixes it.
If you really want to replace them I have usually found that sears is actually pretty good about having and getting parts from.

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we do not have children or pets. I still plan on getting a set of new sensors, but would like to disable them for the ten days it will take for online ordering and shipping......
to remove, can I just take the wires off the screw tabs where they are hooked up ?
James
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Seems they thought of that. Looks like they recognize being disconnected. I suspect the correct value resistor across the terminals would do it but it looks like what most people do is take them off and mount them close to each other above the opener. They seem to be fairly generic so lowes or home depot might have some that you could replace with.

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you cannot disable them. I have tried everything that I know.
and, is the sensors are not working (and I am sure now that mine aren't), putting them close together does no good.
I will just have to lower the door manually until i can get the sensors..........
thanks to all for your comments.........
James
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