Sears garage door opener question

lihpgJune 28, 2008

Greetings. I have read many helpful replies to questions about Sears garage door openers here, and IÂm hoping I can receive the same. IÂll list the symptoms and what IÂve done to try and check things out. IÂm guessing that IÂve lost the sensors or the logic board, but please let me know what you think.

Sears model 139.53673SRT1 ½ hp from 10/97.

It worked fine for 10 years. Starting the other day it will not close the door. It starts, moves a few inches, then stops abruptly and the light flashes, as if there were something in the path between the sensorÂs sender and receiver eyes.

The door moves freely when disconnected. The override (pressing and holding the hard-wired switch) works fine. So, this does not seem to be a mechanical problem.

After using the override to get the door closed, the door will open normally using either the hard-wired switch or the remote.

Changing pressure settings makes no difference.

I can see no glow (green or yellow, although the plastic appears green on both) on either the sender or receiver, making me wonder if power is reaching them. At the motor unit, I read 30 volts being sent to the hardwired switch and just 3 volts being sent to the sensors. I also tried shining a TV remote into the receiver, as was suggested in this forum. No glow in response.

I can place the sender and receiver eye to eye without changing the behavior, so I assume alignment is not the issue.

The remote works fine, in terms of activating the motor. Jumping across the sensor (putting a jumper wire across poles 2 and 3) just defeats the remote. (This, IÂm sure, reveals a noviceÂs mental model; just including it to be comprehensive here.)

I see a blinking yellow light on the rear of the unit (2 blinks then wait; repeat), which I imagine simply means the remote signal is being sought.

We recently had lightning storms, and the door opener problems may have coincided, but IÂm not 100% certain of the timing. I removed and examined the logic board and can see no visual evidence of a strike.

So, is 3 volts normal, implying sensor or wiring problems? Or is this half of what the unit should be putting out, meaning a logic board problem? Or something else that would account for problems exclusive to door closing? Thanks for any advice.

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2 blinks of the LED on the rear of the motor unit means "sensor shorted or wires reversed."

    Bookmark   June 30, 2008 at 2:32PM
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Don, Thanks. I'm glad I was thorough in the description.

I think I can rule out "wires reversed" because they were not touched when this occurred, and I have verified that they are located where, according to other messages, they belong--red stripe (from wall switch) to pole 1 (red), three white (from wall switch and sensors) to pole 2 (white), and 2 black stripes (from sensors) to pole 3 (black).

To try to locate a short, I disconnected the wires to the sensors from the unit then sent power to each (independently, using what I have access to--an AC/DC adaptor--to control voltage). The sender lights up green. The receiver will flash green, but I can't get this to happen consistently. Reconnected to the board, together or independent, neither sender nor receiver lights up, and the problem persists. (And in the midst of this I got 4 flashes from the unit warning light.)

I infer this to mean one of two things. First, there may be a short on the board, since I can get the sender to light up with a different power source. But putting a meter on the two sources (unit and AC adaptor) shows only about a 3V difference, with more from the unit. Trying to rule out some sort of shutdown or load issue when the sensors are attached, I do find more of a drop with the unit (7 to 2.5V) than the adaptor (5 to 4V).

Alternatively, maybe there is something amiss with the receiver. But if so, why would the sender not light up from the unit, regardless?

The puzzle continues ... I'd be grateful for any further thoughts.

    Bookmark   June 30, 2008 at 9:49PM
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As you well know both sensors are connected to the same terminals. If the receiving unit is shorted it could cause the light in the sending unit to not light. Try disconnecting the receiving sensor at the terminals and then see if the sending unit lights. Won't fix anything but will verify our diagnosis.

    Bookmark   July 1, 2008 at 2:31PM
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Don, Yes, I tried connecting the sender and receiver independently to the terminals (i.e., one at a time with the other completing disconnected). No light comes on in either case.

    Bookmark   July 1, 2008 at 4:10PM
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Unfortunately there is still the possibility that it is the logic board and the fact you had s storm pass through almost cinches it. The components on that board are sensitive to surges. Leaves us still in the air and I can't help you with the voltages as I never ever had a reason to check them. If you live in a large enough area you might call around and see if anyone has a used board they will sell you. They change these openers out on a daily basis.

    Bookmark   July 1, 2008 at 5:40PM
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Thanks Don. You have been very helpful. I'll seek to swap out the board, and I'll post the results so that others might learn from the experience. Best wishes.

    Bookmark   July 1, 2008 at 9:10PM
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Don (and others), Here are the results.

I had things narrowed down to the receiving sensor or the logic board. On the promise of a return if parts were in shipped condition, I ordered the sensors, which come as a pair, and the logic board. I wanted to be able to test out both quickly and be done.

Attaching the new sensors directly to the unit, I found everything worked fine. So, it was not the logic board. It had to be the receiving sensor so I replaced it by splicing in at the door. And the opener still did not work!

I started down the list of possibilities again, for example, I considered whether it might be just a short in the wire to the receiving sensor. But to test that I'd need new wire.

Before running for wire, I decided to make absolutely sure other possibilities were eliminated. If the new sending and receiving sensors worked at the unit but not at the door, the problem had to be a wire.

I swapped the new sending sensor for the old one. And everything works fine! In other words, the problem was (at least) the sending sensor, even though that sensor would light up from an external source which had a slightly higher voltage.

An interesting puzzle solved. Thanks again.

    Bookmark   July 7, 2008 at 1:31PM
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