................................................................................. | YDC 28V | msg. no. | Possible Causes: | | DC high | 22-21007 | 1. Excessive 28 VDC voltage applied to Yaw Damper | | | | Coupler | | | | 2. Yaw Damper Coupler | | | | | | | | Corrective Action: | | | | 1. Make sure that the voltage to D295 pin 4 is | | | | between 22.0 and 29.5 volts DC with the Yaw Damper | | | | DC circuit breaker closed. | | | | 2. If the problem is not corrected, replace the | | | | Yaw Damper Coupler (AMM 22-12-31/401). |
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH 10-62253 ú

 22-12-01
 YAW DAMPER COUPLER  ú ú 02 Page 110 ú Jul 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 ~............................................................................... | FAULT MESSAGE/CORRECTIVE ACTION (TABLE 101) | ................................................................................. | YDC Fault | YDC Fault | Corrective Action | | Message | Detail 1 | | .................................................................................
 | YDC 28V  | msg. no.  | Possible Causes:  |
 | DC low  | 22-21008  | 1. Low or No 28 VDC voltage applied to Yaw Damper  |
 |  |  |  Coupler  |
 |  |  | 2. Yaw Damper Coupler  |
 |  |  |  |
 |  |  | Corrective Action:  |
 |  |  | 1. Make sure that the Yaw Damper DC circuit breaker  |
 |  |  |  is closed.  |
 |  |  | 2. Make sure that the voltage to D295 pin 4 is  |
 |  |  |  between 22.0 and 29.5 volts DC.  |
 |  |  | 3. Inspect electrical connectors for bent or broken  |
 |  |  |  pins, contamination, or damage.  |
 |  |  | 4. If the problem is not corrected, replace the  |
 |  |  |  Yaw Damper Coupler (AMM 22-12-31/401).  |

 ................................................................................. | YD sol | msg. no. | Possible Causes: | | short | 22-21009 | 1. Yaw Damper Engage Solenoid | | | | 2. Yaw Damper Coupler | | | | | | | | Corrective Action: | | | | 1. Make sure that the resistance from D295 pin 20 | | | | to ground is between 50 to 80 ohms. | | | | 2. Do a wiring check between D295 pin 20 and D291 | | | | pin 1 at the Yaw Damper Engage Solenoid. | | | | 3. Do a wiring check to ground from D291 pin 2 at the | | | | Yaw Damper Engage Solenoid. | | | | 4. Inspect electrical connectors for bent or broken | | | | pins, contamination, or damage. | | | | 5. If the problem is not corrected, replace the Yaw | | | | Damper Engage Solenoid (AMM 22-12-21/401). | | | | 6. If the problem is not corrected, replace the | | | | Yaw Damper Coupler (AMM 22-12-31/401). |
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH 10-62253 ú

 22-12-01
 YAW DAMPER COUPLER  ú ú 02 Page 111 ú Jul 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 ~............................................................................... | FAULT MESSAGE/CORRECTIVE ACTION (TABLE 101) | ................................................................................. | YDC Fault | YDC Fault | Corrective Action | | Message | Detail 1 | | .................................................................................
 | PR sol  | msg. no.  | Possible Causes:  |
 | short  | 22-21010  | 1. Pressure Reducer Bypass Valve  |
 |  |  | 2. Yaw Damper Coupler  |
 |  |  |  |
 |  |  | Corrective Action:  |
 |  |  | 1. Make sure that the resistance from D295 pin 31  |
 |  |  |  to ground is bewteen 50 to 80 ohms.  |
 |  |  | 2. Do a wiring check between D295 pin 31 and D7377  |
 |  |  |  pin 1 at the Pressure Reducer Bypass Valve  |
 |  |  |  solenoid.  |
 |  |  | 3. Do a wiring check to ground from D7377 pin 2 at  |
　
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