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TROUBLE  PROBABLE CAUSE  ISOLATION PROCEDURE  REMEDY 
Column force and autopilot travel out of limits on one hydraulic system only. Column force normal, autopilot travel not within limits. Excessive force required to move control columns, power off.  Hydraulic pressure from feel computer. Defective power control unit. Excessive elevator friction or elevators out of balance. Binding elevator tab lock linkage.  Check if feel computer differential pressure switch light is on. If light is not on, check hydraulic pressure from feel computer. Check per 3), trouble-shooting item: Column force below minimum tolerance and autopilot travel excessive. Examine data from Autopilot Authority. Check 27-31-0 A/T. If travel is not within limits with hydraulic system A off and B on, problem is with right PCU. Test elevator feel forces balance per instructions in 27-31-0 A/T and 27-31-41 R/I. Disconnect elevator tab pushrods and check for worn or defective components.  Replace feel computer. Replace power control unit. Replace elevators per instructions in 27-31-41. adjust elevator balance panels, or replace components showing excessive friction. Replace components as necessary (Ref 27-31-121 R/I. 

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TROUBLE  PROBABLE CAUSE  ISOLATION PROCEDURE  REMEDY 
Excessive force required to move control columns, power off. (Cont) Faulty elevator centering, power on.  Faulty PCU Excessive friction in elevator control system. Defective centering unit. Elevator control system out of rig. Excessive play in elevator surface.  Individually disconnect lower PCU rod end at structure and manually cycle yoke. Check elevator breakout force at column. If it exceeds 7 pounds for up elevator, or 7.5 pounds for down elevator, system friction may be too high. Check for loose worn or defective parts. Check for rubbing or misaligned cables. Check for foreign objects interfering with system. Check for excessive stiffness in the elevator input Torque Tube/Elevator feel and centering unit support bearings. Check elevator breakout force at column. If it is less than 3 pounds for up elevator or 3.5 pounds for down elevator, centering unit may be defective. Disconnect centering unit input rod from lower torque tube. Check breakout force required to move centering unit input crank. Rod force at breakout is 10 pounds minimum and 14 pounds maximum. Move centering unit input crank by hand up and down. Centering of crank should feel stiff with no backlash. Check for proper rigging of elevator control system (Ref 27-31-0 A/T). Refer to trouble shooting item: Moderate vertical vibration in aft and forward fuselage.  Replace faulty PCU as required (Ref 27-31-101 R/I) Replace worn or defective parts. Remove foreign objects. Replace defective feel and centering unit. Ref 27-31-151 R/I. Rig elevator control system per 27-31-0 A/T. 

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TROUBLE  PROBABLE CAUSE  ISOLATION PROCEDURE  REMEDY 
Faulty neutral shift operation, power on. Excessive airplane pitch-up or pitchdown when both A and B flight control switches are moved to STBY RUD.  Neutral shift mechanism out of rig. Defect in neutral shift mechanism. Interference or binding of centering unit. Defective centering unit. Elevator tab out of rig.  Check for proper rigging of neutral shift mechanism (Ref 27-31-0, A/T). Check neutral shift mechanism for worn or defective components. Disconnect centering unit input rod from lower torque tube and mach trim actuator rod end from neutral shift crank. (Disconnect backlash springs if installed.) Rotate centering unit by hand. Movement should be smooth with little effort. Check elevator centering per 27-31-0, A/T. Refer to trouble-shooting item: Faulty elevator centering, power on. Check power off tab rig position per 27-31-0, A/T.  Rig neutral shift mechanism per 27-31-0, A/T. Replace or repair components as required. Remove interference, replace or repair defective centering unit. Correct improper rigging. 
　
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