.  
If problem persists, remove and replace
rudder power control unit.

.  
If problem persists, replace yaw damper
coupler.

500 
May 01/99  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  22-12-01 Page 109 

Ground Test various faults not covered elsewhere 
YD not  msg. no.   YD sw  LATCHED:  TYPE:  Possible Causes: 
engaged  22-21015  /wrg/YDC  NO  . Yaw damper engage switch not engaged during YDC BITE self test . Yaw damper coupler . Autopilot accessory unit Troubleshooting: . Perform the yaw damper coupler installation  test, ref AMM12-12-01, page 401 step 4. . Verify resistance from D295 socket 14 to ground is less than 2.0 ohms with yaw damper engage switch in the OFF position. . Verify wiring between D295 socket 14, yaw damper engage switch, and autopilot accessory unit. . Inspect electrical connectors for bent or broken pins, contamination, or damage. . If problem persists, replace the yaw damper engage switch. . If problem persists, replace yaw damper coupler. . If problem persists, replace the autopilot accessory unit. 
B hyd not  msg. no.   B hyd  LATCHED:  Possible Causes: 
on  22-21016  /sensor  NO  . B system hydraulics not pressurized during YDC BITE servo test . Flight control system B pressure switch . Yaw damper coupler Troubleshooting: . Verify wiring between D295 socket 7 and D816 socket 3 at the flight control system B pressure switch. . Verify connection to ground at D816 socket 2 at the flight control system B pressure switch. . Inspect electrical connectors for bent or broken pins, contamination, or damage. . If problem persists, replace flight control system B pressure switch. . If problem persists, replace yaw damper coupler. 

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YD actr limit  msg. no. 22-21017   YD actr  LATCHED: NO  Possible Causes: . Excessive yaw damper actuator travel . Rudder power control unit position transducer . Yaw damper coupler Troubleshooting: . Verify resistance between: D295 socket 46 and D295 socket 47 is 80 ohms D295 socket 9 and D295 socket 1 is 100 ohms . Verify wiring at the rudder power control unit position transducer: D295 socket 46 and D295 socket 11 D295 socket 47 and D291 socket 12 D295 socket 9 and D291 socket 10 . Verify connection to ground at: D295 socket 1 D291 socket 9 at the rudder power control unit position transducer . Inspect electrical connectors for bent or broken pins, contamination, or damage. . If problem persists, replace rudder power control unit. . If problem persists, replace yaw damper coupler. 
YD actr rigging  msg. no. 22-21018   YD actr /rigging  LATCHED: NO  Possible Causes: . Asymmetric yaw damper actuator travel . Rudder power control unit position transducer . Yaw damper coupler Troubleshooting: . Verify resistance between: D295 socket 46 and D295 socket 47 is 80 ohms. D295 socket 9 and D295 socket 1 is 100 ohms . Verify wiring between at the rudder power control unit position transducer: D295 socket 46 and D295 socket 11 D295 socket 47 and D291 socket 12 D295 socket 9 and D291 socket 10 . Verify connection to ground: D295 socket 1 D291 socket 9 at the rudder power control unit position transducer . Inspect electrical connectors for bent or broken pins, contamination, or damage. . If problem persists, replace rudder power control unit. . If problem persists, replace yaw damper coupler. 

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YDC, PCU incompat  msg. no. 22-21019   YD actr  LATCHED: NO  Possible Causes: . Aircraft wiring . Restricted yaw damper actuator travel 
.  Rudder power control position transducer 
.  Yaw damper coupler 
Troubleshooting: 
.  Inspect D295 socket 17, D295 socket 53, and YDC electrical connector for bent or 
broken pins, contamination, or damage. 
.  Verify D295 socket 17 and D295 socket 53 resistance to ground is consistent with aircraft wiring diagrams, summarized; 
737 MODEL  D295 - 53  D295 - 17 
-100/200/200 ADV RIDE QUALITY  GROUND  OPEN 
-100/200/200 ADV  OPEN  OPEN 
.  Verify resistance between: D295 socket 46 and D295 socket 47 is 80 
ohms 
D295 socket 9 and D295 socket 1 is 100 
ohms 
.  Verify wiring at the rudder power control unit transducer: 
D295 socket 46 and D291 socket 11 
　
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