Stanley Garage door help

Hello, I have been trying to repair Stanley t300 garage door, just put in a new gear housing.
Now what is happening is that when I push the button, motor turns for a few seconds then goes into reverse for a few seconds.
I have disengaged the worm gear from the other gear to see if there was some obstruction, but same thing is happening.
Could anyone provide help or guidance on what it could be, just spent $45 buying the new housing which shattered when the beam fell, but at the time motor worked fine.
Thanks
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On Mar 28, 12:53 am, musahussain_at_gmail_dot snipped-for-privacy@foo.com (vision1227) wrote:

That's the behavior of something binding. I'd go back over everything to make sure something is not out of alignment or bindng somewhere. Try spinning the motor shaft by hand.
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Or could he have accidently moved one of the limit settings, eg the down force, when making the repair? Seems more likely something is binding though, because I would think even with the force set to lowest, with no door connected, it would still run. And if something other than force is stopping it, eg light beam sensors, then I don't think it would start to begin with.
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wrote:

disconnect door from opener try door it MUST move easily and smoothly.
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wrote:

Actually I have seen some of them start to move and then decide that a sensor was tripped and revrese. Worth checking. Along with confirming that the sensor wires are connected properly. Mine here at this house is so old it doesn't have those so I always forget about them.
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Oren wrote:

I have two garage doors with sensors. The sensors are mounted atop the motor, about six inches apart.
Never had a problem with them being out of alignment.
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you know the sensors yu disabled could of saved a life someday.
think door coming down on animal or child, or coming down and harming your vehicle
the sensors are reall important
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Even the openers with sensors reverse when excessive force is required to close or open the door. Besides don't you believe in Darwin?
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vision1227 wrote:

Have you checked the screw jack mechanism attached to the gearbox? It operates the limit switch on the circuirt board (thing sticking over the long slot cut into the board) through two adjustable plastic tabs (they're what adjust when you turn the small knobs on the bottom of the opener to set the limits of door travel) and attaches to the rear of the board through 4 screws:
http://www.electro-tech-online.com/attachments/repairing-electronics/31372d1247409661-strange-problem-garage-door-opener-stanley_cb.jpg
The limit switch can be manipulated manually with a chopstick or plastic pen (don't use metal, as there's exposed high voltage in the opener, including at some spots on the circuit board) to make the opener stop or start. Could this screw jack have come unsychronized when you fixed the gearbox? BTW if you remove the screwjack to check the motor, the motor won't run forever but will probably stop in 15-30 seconds because there's a time-out safety feature.
Unless the Stanley T300 is from the 1980s or earlier, it measures force by measuring the motor RPM with either a round magnet or a slotted cylinder on the shaft. Could the sensor for it be bad? Optical sensors get dusty, but all sensors can have problems because of poor wiring.
How's the motor capacitor? It's a cylinder about 1-2" diameter, 3-5" long. If it fails, the motor will barely run.
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