Can't adjust UP and DOWN limits on old Chamberlain opener
I just changed the belt on old Chamberlain 3280 opener (41ab050 control board). Starting fully open, the door (or the trolly only with the door disconnected) closes, flexes the bar (as though wanting to close more) then automatically reverses course and opens all the way being stopped only by the stop screw with a thud (going too far open).
For the Down Limit, I turned it clockwise and was eventually able to get to not fully close. However, it still reversed and re-opened. I tried to adjust it back down a bit, but the screw is not reliable (same position doesn't equal same door / trolley result). Unfortunately, the trolley will now only go to up position (even with the screw completely turned clockwise) and is now stuck in the up position. Pressing the door opener only elicits a buzz.
Before this, I tried to adjust the UP Limit (counter clockwise), but never got it to reduce the UP Limit and it would always bang against the stop screw. Eventually this resulted in over-doing it and the screw detached. I had to take the cover off and reattached the plastic screw into its clips.
Any advice would be appreciated. It would be nice if I didn't have to replace the whole unit.