Cant open front of wall opener controll to replace Unit has large white square to open and close door plus a light and lock switch. Unit goes to lock each time we use the remote or wall mount. Switchmaster security plus

They have self diagnostic features and are 'smart'. Make sure there is nothing near the two door sensors and make sure they are clean. No model number given, but generic help in the link.

https://www.google.com/search?q=Liftmaster+Wall+Control+Large+White+Button+green+light+is+not+illuminated

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Is the wall switch in the 'locked' position? Look for small slide switch.

disconnect motor, check the door is operating smooth and correct. check springs. check downward pressure setting

Lift the door handle as if you were opening it

Hold the handle & use a round phillips to hook
& rotate the white door latch to the open position

Sounds like you have a couple problems. The opener is in the lock mode which is the reason the remotes will not work. Press and hold for 3 seconds the button on the wall control that has the icon of a padlock on it. This will unlock the opener and your remotes will work. If when you try to close the door the main light flashes 10 times when the door reverses to the open position it is a door sensor problem. One of the small lights on the sensor may be flickering ever so slightly. Tweak them a bit and try. If this isn't the case and the main light is not flashing you can try increasing the down force just a tad. This control is on the rear of the motor unit near where all those white wires go. Increase this just a bit and try. If this doesn't work you most likely have a bad RPM sensor board which is a small printed circuit board just in front of the motor. It will cause this problem.

I think the trolley has jammed against the bolt just in front of the motor unit. Remove the bolt and then run the door until it is closed. With the door closed locate the 'up limit' control on the side of the motor unit. Turn this 2 turns in the opposite direction of the arrow printed on the cover. Replace the bolt.

There are certain models that had only a door bell type wall control and didn't have the lock and light functions. You may have one of these and someone has replaced the wall control with the three button model. If it did work in the past and has quit it is most certainly the logic board and is expensive to replace.

You say it is STILL stuck in the "lock" mode. If you cannot use your remotes you need to program it. Find the smart/learn button just to the left of all those white wires. Press and hold the button on a remote while you press and immediately release the smart/learn button. Do this for each remote.

UNPLUG THE UNIT AND WAIT 5 MINUTES.
THIS WILL RESET THE CONTROLS.

SEE IF THE WALL BUTTON LIGHTS UP.

IF THIS DOESN'T SOLVE IT GOTO CHAMBERLAIN.COM AND DOWNLOAD THE MANUAL (FREE PDF FILE) IT WILL TAKE YOU THROUGH A COMPLETE DIAGNOSTIC.

HOPE THIS IS HELPFUL

a component in the wall unit is failing , that makes the conection happen when the remote signal is recieved , ( it is recieving the remote signal but not sending it out to the control circuit for the motor )

If the wall station is flashing the lock button is on Push and hold the lock button for 2 sec. and release. The light should be solid(not flashing) For you door opening part of the way: If you have a Chraftsman/Liftmaster:
 1.Check to see if the door is running correctly.
  A. Run the door down and pull the emergency release. See if the door will run easily by itself.
    1. If it runs hard by hand try lubricating the rollers and hinges with silicone spray or some form of lubricant (not WD 40)
    2. If the door is heavy and falls back to the ground, you probably have a spring issue (either broken or needs more tension) in this case call a professional door repair company in your area.
  B. If the door runs fine then check the up and  down force on your operator (the box that hangs from the ceiling). If the light bulb(s) on your operator are on the front and/or back, the force adjustment screw is on the back of the operator. If the lights are on the sides of the operator then the force adjustment screw is on the right side (looking from the back of the operator and facing  the garage door). Turn the light blue adjustment screw with the up arrow to a higher number.
C. If this does not solve your problem the top bushing could be going out of your operator. Open the case and see if a lot of black filings are on the top of the big gear. If so the gear assy. will have to be replaced part # 41C4220A