Garage door sensors losing power

I'm having trouble with a 9 year-old Overhead Door Legacy garage door.
The sensors work fine when the door is within 2' of closed, but they both lose power (both lights, green on one sensor, red on other, go out, and the sensor voltage at the motor unit goes to zero) as the door opens. Sometimes they come back on as the door nears 4' of closed, always back on within a foot or two.
Symptoms lead me to believe I have a lose connection somewhere, but I don't know much about garage door openers. Anyone know how the short would be related to the garage door's position?
I've gone over the wiring looking for a bad connection and haven't found anything, wondering if the main unit may be causing the problem.
Thanks for any help, Mark
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Your first sentence is pretty accurate.
I just love it when the average schmoe ASSumes that anything electrical not working is a "short".
If it was a "short", the damn circuit would've fried (and/or popped a fuse or breaker).
you most likely have some kind of intermittent open circuit condition breaking a signal path & causing a malfunction.
do yourself a favor and call a pro.
anyone who can't tell the difference between a "short", and an open circuit shouldn't be messing around with wiring.
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A schmuck that can't read and comprehend shouldn't respond to posts. The referral to short was only a generalization not a diagnostic assumation. Do yourself a favor and pick up a pre-school book and study...
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The "pro" in this area will replace parts until it starts working, charging $75 for the visit plus the cost of the parts. While I'll probably end up doing that I see no harm in trying to identify/fix the problem myself, it may be something simple. While I misused the word "short" the open connection may be easy to trace, I don't plan to "mess around" with anything and I have an electrician friend who will help.
Thanks for all of *your* help, you've certainly brightened my day! :-)
Mark
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Renderdog wrote:

I would guess that it must be something in the control unit. Thinking of a poor solder joint on a circuit board. But that would not explain why it would lose power relative to the position of the door. Still, if you open the unit it would be worth while to go over the joints with a solder iron. Sometimes the joint looks fine until you look at it with a microscope.
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find model number, search google.com for the manual to see if it has troubleshooting.
see why to replace it at: http://groups.google.com/group/alt.home.repair/browse_frm/thread/1fe9595ad65d99ab/24fe143b0c997988?lnk=st&q=%22Overhead+Door+Legacy%22+problem&rnum=1&hl=en#24fe143b0c997988
here's installation with drawings of one: http://www.popularmechanics.com/home_improvement/home_improvement/1276316.html?page=2&c=y
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Maybe a problem with the wire itself? Is the wire attached to the door track or is it run near the springs? I suspect it is a problem with the circuit board in the opener.
--
Joseph Meehan

Dia duit
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Renderdog wrote:

I assume you are talking about sensors to open the door if it shuts on an object (like you). Sensors may be disabled at the very end so they don't reverse the door as it hits the actual floor. The disabling switch, or mechanics that operate it, may be the problem.
bud--
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