Sounds like a bad capacitor, bad limit switch, bad circuit board or
stuck button. If it was a gear, the motor would usually run until you
hit the button to stop it & not usually run for just a couple of
Unplug opener, remove cover, if it looks like it snowed inside, the
gear is shot, if you see what looks like oil in the cover the capacitor
is blown. Sometimes the capacitor itself will show it is obviously
If nothing appears obvious the challenge becomes in determining which
part is bad when you don't have a truck full of parts sitting in your
driveway. The opener could have run thru a limit & jammed to where the
motor doesn't have enough power to unjam it. The motor capacitor could
be bad to where it doesn't give the motor the starting power. The
circuit board could be faulty & is actually telling the motor to run in
both directions at the same time. A button could be stuck.
First unhook the wall button wiring at motor head to see if
transmitters work. If not remove all transmitter batteries & jump
across terminal screws on motor head to see if it now works. If not,
try spinning the motor shaft (w/ opener unplugged & door disconnected)
to get the opener in the half way position. Plug in opener to see what
happens. Will the opener run one direction & not the other (bad board)?
If motor just hums try to spin the motor shaft (carefully while unit is
humming) & see if it runs (bad capacitor). If motor still won't start
tap on circuit board relays (there are 3, light, up, & down) lightly to
free up a stuck relay contact. If the motor does run verify that the
limit switches will shut it off & not simply run thru them.
As you can see there are a number of possibilities & "humming" doesn't
always have the same fix.