Scenario: If the door closes and reverses and the light bulbs do not flash, here are some possible causes to the problem:
1. DOWN TRAVEL OUT OF ADJUSTMENT
2. DOOR MAY BE OUT OF BALANCE (SPRING PROBLEM)
3. WORN GEAR / SPROCKET
4. BROKEN / BENT LIMIT SWITCH ASSEMBLY OR BAD LOGIC BOARD
1. DOWN TRAVEL OUT OF ADJUSTMENT
POSSIBLE SOLUTION:
When the door touches the floor before the opener’s limit reaches it closed set point, the unit will feel the resistance of the floor and the door will reverse as system is designed to do. You will need to reduce the down limit travel adjustment screw or button, making sure to door closes in the proper position (not over traveling).
2. DOOR MAY BE OUT OF BALANCE (SPRING PROBLEM)
WARNING:
To prevent possible SERIOUS INJURY or DEATH: ALWAYS call a trained technician if your garage door binds, sticks, or is out of balance. An unbalanced garage door may not reverse when required.
NEVER try to loosen, move or adjust garage door, door springs, cables, pulleys, brackets or their hardware, all of which are under EXTREME tension.
POSSIBLE CAUSE:
The problem could be that the door is too bottom heavy. The opener motor is not made to handle the weight of an out of balanced door. If the door is too heavy, door can travel down a bit faster than the motor causing the travel limit set point to drift. This will cause the door to reach the closed position before the limit switch assembly reaches the closed set position. This will cause the limits to come out of adjustment.
POSSIBLE SOLUTION:
Perform these steps to test the proper alignment and balance of the garage door .
•Close the garage door.
•Disconnect the garage door from the garage door opener
•Pull the manual release rope down and back towards the motor unit to disconnect
•With the door still disconnected, open and close the door by hand. The door should move easily with one hand. If the door sticks or binds, remove any obstructions and lubricate the door rollers, and hinges. After lubricating the door check if the door is still sticking or binding. If you are unable to resolve the sticking or binding issue, contact a professional door technician
• Open the door half way and then release it.
• The door should remain in place completely supported by its springs.
• If the door slowly rises upwards or falls to the floor gently, this is acceptable.
• If the door slams shut or shoots upward with force, the door is out of balance.
If the door fails the balance test, contact a professional door technician.
If the door passes the balance test and is not sticking or binding, reattach the door to the opener:
Activate the garage door opener and the door will automatically reconnect.
Note: If the door is the problem, you can reduce the down travel again; but the problem will persist until the springs have the proper tension to carry the weight of the door.
3. WORN GEAR / SPROCKET
The bearings in the sprocket can wear out. When this occurs the sprocket will start to move side to side, causing the sprocket to turn at an angle. This causes the helical gear (inside the motor) not to mesh with the drive gear on the limit switch assembly. If this happens the motor will cause the sprocket to spin but since the helical gear is not meshing with the drive gear on the limit switch assembly, the center limit contact will not move towards the down contact to close the circuit. The motor will keep running until it feels the resistance of the door hitting the floor and then causes the door to reverse.
POSSIBLE SOLUTIONS:
First unplug opener, check if the bearings in the sprocket has worn out. You will have to loosen the belt or chain, remove the sprocket cover and grab the sprocket and move it side to side. Do not try turning the sprocket just move it side to side. If it moves side to side then the gear and sprocket assembly needs to be replaced.
If the sprocket does not move side to side, the gears may be stripping out inside the unit. To determine if the gears are stripping out, you will have to remove the metal cover and inspect the gears inside the unit. If you see the gears all chewed up or white shavings on the housing the gears need to be replaced.
4. BROKEN / BENT LIMIT SWITCH ASSEMBLY OR BAD LOGIC BOARD
POSSIBLE SOLUTIONS:
If you have reduced the down travel by at least 7 full turns and the problem persists, you will have to remove the metal cover and inspect the limit switch assembly. When the metal cover is removed, look for the limit switch assembly and observe the limit switch assembly while the door is closing. When the door reaches the closed position, it should touch the down limit contact.. When the center contact and the down contact touch it closes the circuit and the logic board should then send the signal to the motor for it to shut off.
If the center limit contact does not touch the down contact (brown) when the door reaches the closed position, then make the proper adjustments using the white plastic adjustment screw.
If the center contact does touch the down contact and the center contact keeps pushing against the down contact, make sure that the center contact is not bent. Also, check for any loose wires. If the center contact is not bent and the wires are in place snug and the center contact continues to push against the down contact then the logic board needs to be replaced.
If the center contact is bent or broken then the limit switch assembly has to be replaced.
After ANY adjustments are made, the safety reversal system MUST be tested. The door MUST reverse on contact with 1-1/2″ high (3.8 cm) object (or 2X4 laid flat) on the floor.
This information was taken from LitfMaster.com