My garage door opener (Craftsman 1/2 HP) stopped working some time ago (even lights didn't come on). I replaced the circuit board and now the lights are working and the board reacts to the remote (rapid blinking) but the motor doesn't start (doesn't even make a noise). I decided to replace the motor but it didn't help. There is a large capacitor between the CB and the motor. When I press the remote my voltage meter doesn't show anything on that capacitor's legs. Could it be the capacitor?
When I was working on modifying my garage door opener, I found two things:
One of the failure sensors was tripped; there are several, but the one that got me was the obstruction sensor. It was incredibly easy to bypass by short-circuiting the sensor's connection with a jumper wire.
The communication may be off, especially since you replaced the board and remotes sometimes don't clear their memory so well; check the blink patterns in the diagnosis manual. The blinks may indicate that the remote's rolling keycode pattern is incorrect. This is exactly what happened to me.
No voltage at the capacitor may mean it is never getting current to be charged. There is some sort of relay that the computer triggers to run the motor. That is a likely failure point in the system.