My garage door will not open but approx. 8" , no cable broken , chain on track. Today I found that one spring is broken. how hard is it to replace.

They are not light weight but there is no reason if the motor can raise it, then you cannot raise it by hand.

1. disconnect the door from the chain. 2. inspect the door again, try oiling the rollers and joints. It is the chain that lifts the door. Try manually lifting the door. If it still does not lift open, it is the door and not the Opener unit. 3. Although you don't see kinks, look for any obstructions eg. the track. 4. Make sure the track has not lossened out at any point. 5 If you can lift the door,. connect with the chain. Goog luck. Basically I think it is the door mechanism that has some how misalligned.

open your garage door , when the door is going up block with your hand one sensor eye , if your door going down ,you have inverted down-up cycle if not mother board is damaged youll need remplaced

My plastic gear stripped soon after a spring broke. I think the broken spring put a huge load on the opener that day and ruined the gear. Replacement wasn't too hard. It will be obvious when you remove the cover if the gear is stripped. Here are instructions:
http://tinyurl.com/gearfix

You need to call a door technician. The bottom rollers are usually connected by a cable to the door spring and can be dangerous.

You probably have a broken torsion spring. If you have a spring on a shaft above the door (usually 2 if it is a double door) then you have a torsion spring. From this shaft you have a 2 cables wound on a drum going down to the bottom of the door. If it is a single door, then this cable will be loose. If you have a double door, then most likely one spring is broken. This allows the door to open slightly, until one side is trying to lift(good spring) and the other side cannot (broken spring) Unless you are an EXTREMELY CONFIDENT DIYer then you should leave this do a door repairman as winding a torsion spring is dangerous, and can break bones or even kill. Now if your door has extension springs on each side of the track,with a pully and cable, then these can easily be replaced yourself. Check that cables are connected to the springs and the door and that one didn't break or come loose or cable off pully and binding.

check the track system to make sure all the wheels are in track and/or there are no obstructions preventing it from opening, it may be equipped with an emergency shut off if there are any obstructions, also, make sure track is well greased, too dry of a track causes alot of friction.

check with your model number on chaimberlain's manual download page here:

http://www.chamberlain-diy.com/doityourself/support/manuals

Too much tension on the door can make the "brain" respond by opening the door, thinks something is in the way.... check for binding tracks or wheel guides, loose bolts, dry chain, tension on cables or springs ( be careful here), misaligned sensors....

Sounds like a bad spring or the drive gear is going bad. Take a good look at the springs above the door. It is sometimes hard to tell when one is broken. Remove the cover and look at the gear. It is obvious when this is going bad.

pull the rope attached to the garage door opener.  And get a friend to help you lift the door.