I did that.
Chain doe's not move.
Motor just hums a few seconds and then shuts off.
The long part of the Chain is slack and the short part of the chain that runs around the sprocket and connects to the cable is under pressure.
Sounds to me like your motor is bad...Or the chain is misaligned...You would have to remove the chain to see if the motor will spin....But most likely the motor is bad...
I removed and re-installed the drive chain.
Door goes down as long as I hold down the button. If I let off the button it does not stop, it reverses.
Bob thought the motor was bad or the chain was misaligned/binding, they weren't.
My last question to Bob " Door goes down as long as I hold down the button. If I let off the button it does not stop, it reverses." he never answered this reply/question.
I ask that same question to a garage door company a they said it is the safety reverse system, so I am going to go with that answer.
When we first started you said the chain was loose on one end that the sprocket was under pressure...You replied that you readjusted the sprocket and now it works...So now the motor is spinning not humming and frozen up...Your second problem was the door goes down and will reverse once the button is let off....I was not able to get back to you right away with your second question.....I apologize....By not being there infront of opener and not actually looking at the opener..there could have been a fe varations..the limit switch...Door sensor position...Etc....Glad you have it fixed...
You did not timely respond to my last question, a garage door company did.
Thanks for trying.