................................................................................. | YD EHSV | msg. no. | Possible Causes: | | fault | 22-21013 | 1. Yaw Damper Transfer Valve | | | | 2. Yaw Damper Coupler | | | | | | | | Corrective Action: | | | | 1. Make sure that the resistance between D295 pin 30 | | | | and D295 pin 32 is 2000 ohms. | | | | 2. Do a wiring check between D295 pin 30 and D291 | | | | pin 8 at the Yaw Damper Transfer Valve. | | | | 3. Do a wiring check between D295 pin 32 and D291 | | | | pin 5 at the Yaw Damper Transfer Valve. | | | | 4. Do a wiring check between D291 pin 7 and D291 | | | | pin 6 at the Yaw Damper Transfer Valve. | | | | 5. Inspect electrical connectors for bent or broken | | | | pins, contamination, or damage. | | | | 6. If the problem is not corrected, replace the Yaw | | | | Damper Transfer Valve (AMM 22-12-21/401). | | | | 7. If the problem is not corrected, replace the | | | | Yaw Damper Coupler (AMM 22-12-31/401). |
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 22-12-01
 YAW DAMPER COUPLER  ú ú 02 Page 114 ú Jul 12/01 
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A 
737-300/400/500MAINTENANCE MANUAL
 ~............................................................................... | FAULT MESSAGE/CORRECTIVE ACTION (TABLE 101) | ................................................................................. | YDC Fault | YDC Fault | Corrective Action | | Message | Detail 1 | | .................................................................................
 | YDC 26V  | msg. no.  | Possible Causes:  | 
 | AC fault  | 22-21014  | 1. Rudder Power Control Unit  | 
 |  |  | 2. Yaw Damper Coupler  | 
 |  |  | 3. DAA  | 
 |  |  |  | 
 |  |  | Corrective Action:  | 
 |  |  | 1. Make sure that the resistance between D295 pin 9  | 
 |  |  | and D295 pin 1 is 100 ohms.  | 
 |  |  | 2. Do a wiring check between D295 pin 9 and D291  | 
 |  |  | pin 10 at the Rudder Power Control Unit position  | 
 |  |  | transducer.  | 
 |  |  | 3. Do a wiring check to ground at D295 pin 1.  | 
 |  |  | 4. Do a wiring check to ground at D291 pin 9 at the  | 
 |  |  | Rudder Power Control Unit position transducer.  | 
 |  |  | 5. Do a wiring check between D295 pin 9 and D2165B  | 
 |  |  | pin C14 at the DAA.  | 
 |  |  | 6. Inspect electrical connectors for bent or broken  | 
 |  |  | pins, contamination, or damage.  | 
 |  |  | 7. If the problem is not corrected, replace the  | 
 |  |  | Rudder Power Control Unit (AMM 27-21-91/401).  | 
 |  |  | 8. If the problem is not corrected, replace DAA-1  | 
 |  |  | (AMM 34-28-41/401).  | 
 |  |  | 9. If the problem is not corrected, replace the  | 
 |  |  | Yaw Damper Coupler (AMM 22-12-21/401).  |
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