Garage door opener interrupter cup

coldnose(N. California)April 30, 2009

I have a classic garage door opener problem: motor moves chain about a foot, then reverses it about a foot and stops. Happens just the same with the door engaged or disengaged.

I've checked the archives which tell me I should probably be looking at the interrupter cup and maybe the rpm sensor.

My question is: how difficult are these parts to access generally on an older Craftsman 1/2 horse chain unit. Are they fairly accessible with the unit in place after removing the cover, or will I have to take it down? Anyone ever done this or familiar with it?

(The problem opener is on my folks' garage in another town. I'll be visiting soon so I'm trying my best to anticipate what I'm up against!)

Thanks as usual for any help!!

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coldnose(N. California)

oops...wrong forum probably...

    Bookmark   April 30, 2009 at 9:25PM
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mayhem69(zone 6 SE PA)

hi coldnose. I had the same problem on my Craftsman 1/2 hp. about 1 yr. ago. Well that and some more. First my sprocket on top of the housing broke. I bought a replacement kit from a dealer on Ebay that came with new sprocket, worm gears, etc. After i got all that installed it was now doing the 1 ft. up and down thing like you. So, i finally narrowed it down to the rpm sensor after some research. I called a fairly local garage door installer who had the rpm sensor that i needed. It costed me less than the dealers on Ebay too. Very nice guy who helped me out with some newbie questions also.
After installing that it worked like a charm and has been so ever since.
Just be very careful not to break the 2 little tabs that fit into the holes when installing the board.
Good Luck!

    Bookmark   May 1, 2009 at 1:02PM
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mayhem69(zone 6 SE PA)

sorry coldnose, I really didn't answer your actual question. You will be able to fix this with the unit hanging. Remove the housing screws. Carefully inspect the worm gear if yours has one and other internal parts. Make sure the interrupter cup is pushed all the way onto the shaft. If you can't get it to work messing around with the cup, check the rpm sensor and make sure that is working. Sounds like the rpm sensor to me.
Take it down and get the part #. Then call some local installers and ask them if they have it in stock. Also check E-Bay for alot of good deals. Careful not to break the 2 plastic tabs.
Good luck again!

    Bookmark   May 1, 2009 at 1:12PM
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If the main light flashes 10 times when the door reverses you could be looking at misaligned or bad door sensors. Make sure the small light on each sensor is lit and not blinking. They get bumped quite often.

    Bookmark   May 1, 2009 at 4:08PM
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coldnose(N. California)

Hey, thanks a lot Mayhem and Don.

I don't think there are any door sensors so I guess the model must be pretty old. But it looks great and it's been working flawlessly up until now so I'd like to try to fix it.

At the risk of hyper-extending your ears... if I do need to remove and replace the rpm sensor, did I understand correctly that I should be able to do that too without removing the whole unit from the ceiling? Will it be fairly clear once I'm inside looking at it and, most importantly, what's an rpm sensor look like anyway??!!??

Thanks again from me and my patient, trusting parents.

    Bookmark   May 1, 2009 at 7:16PM
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THere are large pictures that show the interrupter cup and RPM sensor here:

Here is a link that might be useful: liftmaster / sears garage door opener gear replacement

    Bookmark   December 16, 2010 at 7:33PM
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It doesn't get any better than those instructions.

    Bookmark   December 17, 2010 at 6:17AM
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I have a craftsman door opener that is about 12 years old and it started doing the same as yours. I fiddled with the electric eyes to no avail and finally broke out the manual. I don't know if this is your problem but here is what fixed mine.

On the back side of the control box in the lower right hand corner there are two screw adjustments that increase or decrese the "force" on the door opening or closing. I increased mine about about 10 degrees and the problem was solved. Just a thought.

    Bookmark   December 17, 2010 at 10:05AM
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