Originally Posted by
scifi
I know some people are saying that the Stab Trim Cutout switches near the quadrant, cut the circuit to the stabiliser... But is this just the signal circuitry, or all d.c. power to the Screwjack as well.
I thought the Screwjack contains a transistorised power supply circuit that produces an a.c. supply for the brushless motors, which are required to turn the screwjack nut..
The stab trim electric motor is a 270 volt DC motor. However, the aircraft supplies 3 phase 115 volt AC power to the actuator assembly in the tail. Power is converted from AC to DC. The autopilot and the column trim switches provide a smaller dc voltage to the control relays in the actuator assembly. The cutout switches on the quadrant stop the smaller DC signals from reaching the trim switches and also stop (via a big relay) AC power from reaching the actuator assembly.
There are relays and power converters in the tail assembly, but unless the converter is solid state, I can't imagine there are too many transistors there.