As with all mechanical components in a home, an automatic garage door opener requires periodic maintenance to ensure safe and efficient operation. In fact, because the garage door is often the heaviest and largest single piece of moving equipment around a home, frequent testing and maintenance are especially important.      One of the best resources for garage door maintenance is the opener owner's manual. Lubrication requirements and adjustment details are typically found in this manual. If you don't have an owner's manual, you can usually order a replacement copy by contacting an installing dealer or the manufacturer. Some manufacturers even make owner's manuals available on the Internet. All you'll need is the brand and model number.      A visual inspection of the garage door springs, cables, rollers, and other door hardware is a great place to begin. Look for signs of wear and frayed or broken parts. Most minor repairs, such as roller replacement, can be performed by a handy do-it-yourselfer, while more complicated tasks should be handled by a qualified garage-door service technician. The springs and related hardware are under high tension and can cause severe injury when handled improperly.      Rollers, springs, hinges, and tracks require periodic lubrication. Use spray silicone, lightweight household oil, or white lithium grease according to the instructions in your owner's manual.       Periodically test the balance of the door. Start with the door closed. Disconnect the automatic opener release mechanism so that the door can be operated by hand. The door should lift smoothly and with little resistance. It should stay open around 3 to 4 feet above the floor. If it doesn't, it is out of balance and should be adjusted by a professional.      In addition to extending its life, monthly inspection and testing of the automatic opener can prevent serious injuries and property damage. Careless operation and allowing children to play with or use garage door opener controls are dangerous situations that can lead to tragic results. A few simple precautions can protect your family and friends from potential harm.      Never stand or walk under a moving door. Keep transmitters and remote controls out of reach of children and teach them that they are not toys. The push-button wall control should be out of reach of children (at least 5 feet from the floor) and away from all moving parts. The button should always be mounted where you can clearly see the door in full operation.      Test the force setting of the opener by holding up the bottom of the door as it closes. If the door does not reverse readily, the force is excessive and needs adjusting. The owner's manual will explain how to adjust the force sensitivity.       To avoid entrapment, perform the 1-inch reversing test after any repairs or adjustments are made to the garage door or opener. Do this by simply placing a 2- by 4-inch block of wood flat on the floor in the door's path before activating the door. If the door fails to immediately stop and reverse when it strikes the wood, disconnect the opener and use the door manually until the system can be repaired or replaced.      Since April 1982, federal law has required that a closing garage door that is operated by an automatic opener must reverse off of a 2-inch block.       Even with the safety improvements resulting from the April 1982 legislation, injuries continue to occur, and safety is still an issue. Consequently, a new law as of January 1, 1993, requires that a garage door opener must be equipped with a monitored non-contact safety reversing device or safety edge that stops and reverses a closing garage door.      An example of such a safety device is an electronic beam sensor that is installed at either side of the door opening, which, when broken, causes the door to stop and reverse itself.       A second safety feature is a pressure-sensitive electronic rubber strip that attaches to the bottom of the door where it makes contact with the floor. Just as with the beam sensor, when engaged, this safety edge causes the door to stop and reverse itself, avoiding injury or damage to property.      Some of the most common garage door opener problems and their respective solutions are as follows:        If an opener raises but won't close the door, the safety beam sensor may be faulty, misaligned, or unplugged.         An opener that operates by remote control, but not by the wall switch, is the sign of a short in the wiring or a loose connection at the switch.        A remote control that doesn't work may be something as simple as a weak or dead transmitter battery, an antenna wire on the opener that is not properly exposed, or a dead transmitter.        If the opener is operating, but the door doesn't open, it may be due to a worn gear or chain drive sprocket, a broken chain, or the door has disengaged from the operator.        An opener that operates by itself can be caused by a faulty transmitter, a short in the wall switch, a faulty circuit board, or a stray signal -- the latter being very rare.        If the remote control only operates the door when it is located a distance of 25 feet or less from the opener, the battery in the remote is usually weak or the signal is poor.        A door that reverses while closing, or that doesn't completely open or close, is usually obstructed or binding. This condition can also be caused when the open limit or sensitivity is set wrong.