Garage door bounces back open - Sears Craftsman LiftMaster Chamberlain Garage Door Opener Wireless Keypad Model 976LM Security+

What about force setting. It should be set about a little less than half. If it hits the ground and bounces back up even after you positively check the travel limits than its the motherboard/logicboard.

You need to go through the programming again and reset your limits. Your limit was set too far closed causing the door to "bounce".

If the door reverses when it hits the floor it is traveling too far in the down direction. Locate the 'down limit' adjustment on the side of the motor unit. Turn this control in the opposite direction of the arrow printed on the cover. Some tweaking will be necessary to get it just right.

The limit switch of both the sides are not reached. The drive must be realigned to work till the door closes fully so as to touch the limit swittch to switch off.
Similarily the open door must go to the extreme point to cut off with the activation of the limit switch.

Don't tighten the chain. It sounds like you have either a broken door spring or the drive gear in the motor unit is going bad. Release the opener from the door and operate it by hand. It should be easy enough to raise that your wife can do it with no problems and it should stay put when released about waist to shoulder high.

Is there a limit switch to tell it when it is fully closed?

It sounds like the door is traveling too far in the down direction. Locate the 'down limit' adjustment on the side of the motor unit and turn it in the opposite direction of the arrow printed on the cover. Some tweaking of this control will probably be necessary.

On the side of the motor unit you will find the 'down limit control'. Using a small screwdriver turn this control in the opposite direction of the arrow printed on the cover. Some tweaking will most likely be necessary. You can remove the cover and watch the limit switch assembly and get a good idea how it works.

If the door reverses when it hits the floor it is traveling too far. Locate the 'down limit' control on the side of the motor unit and turn this in the opposite direction of the arrow printed on the cover. Some tweaking will most likely be necessary. You can always recognize a sensor problem because the main light will flash 10 times. If the main light isn't flashing it isn't a sensor problem.

Have the power solenoid looked at