27-41-00
ALL ú ú 02 Page 9 ú Mar 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
STAB TAKEOFF WARNING
SWITCH (S546)
(REF 31-26-24)
LIMIT SWITCHES
(AIRPLANE NOSE DOWN)
SEE A
LIMIT SWITCHES STAB AUTOPILOT AND
(AIRPLANE NOSE UP)ELEC ACTUATOR LIMIT SWITCH (S145)SEE A STAB ELEC ACTUATOR LIMIT SWITCH (S844)
SWITCH MOUNTING BRACKETS
CAM
STAB TAKEOFF WARNING SWITCH (S132) (REF 31-26-24)
FWD STAB ELEC ACTUATOR LIMIT SWITCH (S115) SWITCH (S144) STAB AUTOPILOT LIMIT
A
Stabilizer Trim Limit Switches Figure 5
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27-41-00
ALL ú ú 01 Page 10 ú Jul 15/90
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
C. Main electric nose down travel is limited by one of two limit switches as selected by flap position.
D. Refer to AMM 31-26-00/001 and Fig. 5 for takeoff warning limit switches.
9. Stabilizer Trim Relays (Fig. 2)______________________
A. Stabilizer trim relays include the phase sequence relay, trim control relay and trim safety relay. With power applied, the phase sequence relay contacts close and the safety relay holds the contacts in closed position allowing the trim control relay to control switching power directly to the motor for normal operation.
B. The stabilizer trim relays are mounted in the J5 junction box, which is located to the right of the nose gear wheel well. The J5 box can be accessed through the right aft access panel in the nose wheel well.
10. Operation_________
A. Normal control and operation of stabilizer trim is accomplished with electrical power. Control power for the relays and the electromagnetic clutches is 28-Volts DC. The actuating power for the stabilizer trim motor is 115-Volt, three-phase AC (Fig. 2). When the three-phase power source has the correct phase sequence, assuring correct direction of motor rotation, the phase sequence relay contacts will be closed. The clutch and relay control circuits are ready for normal electrical operation only when the main electric trim cutout switch is at the NORMAL position. With power supplied and the trim cutout switch at the NORMAL position, the stabilizer safety relay coil will be supplied 28-Volt DC power to hold the contacts closed. This will allow the trim control relay to control switching power directly to the motor for normal operation. The actuation of either trim control switch will switch control power to energize the trim control relay and the appropriate electromagnetic clutch. This action connects three-phase power to the motor, which rotates in one direction only, and engages the clutch which controls the direction of actuator drive. With the PSTA actuating the jackscrew, the trim wheels will be turned and the trim indicators positioned through the manual system as the manual system is driven from the cable drum on the jackscrew gearbox. The PSTA will continue to drive the jackscrew in the direction selected until the trim control switch is released, the limit switch is actuated, or the cutout switch is positioned to CUTOUT. Limit switch actuation interrupts power to the clutch which disengages the motor. The motor will not be de-energized by limit switch actuation. The trim wheel rotation will stop and trim position indicator will show that the trim action has stopped at the extreme end of travel. Release of the trim control switches will cause the control relay to drop out, interrupting motor power. Switching trim cutout switch to the CUTOUT position disconnects all normal control circuits, shorts all relay and clutch solenoids to ground, and de-energizes the safety relay to open the trim motor power circuit.
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