There was a case some time back on a B757 Freighter on a high security European flight (money) where the local plod insisted on inspecting the landing gear bays. So open the panel underneath, select the Door Arm switch and Doors Open. Nothing. Scratch head, check the books and try again -still nothing. So AOG - same system does the alternate gear. The B767 has the same system.
The system of alternate gear extension are quite different on B757 and B767. the B757 has electrical switches that operate a hyd pump that uses L HYD to power the door locks open.
On the B767 a rotary actuator under the flight deck floor operates a cable system that mechanically opens the door up locks.
Strange that the B767 has mechanical cables under the floor of the flight deck, but a small electrical actuator to operate them. Why not a hatch in the floor like B737? Perhaps the switch is for commonality with the B757, to make the pilots think that two different systems are the same.