(6)  
The following messages are displayed by the yaw damper module:

 (a)  
NO FAULTS - There are no FAULTS NOW and no LAST LEG FAULTS.

 (b)  
NO FAULT NOW - There are no FAULTS NOW but there are LAST LEG FAULTS.

 (c)  
NO LEG FAULT - There are FAULTS NOW but there are no LAST LEG FAULTS.

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MAINTENANCE MANUAL
 (d) (e) (f) (g) (h) (i)  FAULTS NOW - There are one or more FAULTS NOW faults, and they are displayed by pressing the DISPLAY button on the faceplate of the yaw damper module.LAST LEG - There are one or more LAST LEG FAULTS, and they are displayed by pressing the DISPLAY button on the faceplate of the yaw damper module.TEST RUNNING - Power Up Test (PUT) or Pre-Flight Test (PFT) is running on the yaw damper module.ACCEL - The yaw damper module has determined that there is a fault with the modal suppression accelerometer.L ADC, R ADC - The yaw damper module has determined that the data from the indicated air data computer is invalid.ADC DIFF - The yaw damper module has detected an invalid input from an air data computer but is unable to determine which one is at fault.
 (j) (k) (l) (m) (n)  AIRGND 1, AIRGND 1/2, AIRGND 2 - The yaw damper module has determined that the indicated air/ground discrete is invalid.AIR DIFF - The yaw damper module has detected an invalid air/ground discrete but is unable to determine which air/ground relay is at fault.26 VAC - The yaw damper module has detected the loss of or the invalid level of the 26V RMS reference voltage.HYD SWITCH - The hydraulic pressure high signal agreed with the hydraulic pressure low signal for more than 2 seconds.L IRU, C IRU, R IRU - The yaw damper module has determined that the data from the indicated inertial reference unit is invalid.
 (o)  AIRPLANES WITH -124 YDM AND SUBSEQUENT YDM DASH NUMBERS; IRU OFF - The IRUs are not on or no data is transmitted.
 (p)  AIRPLANES WITH -124 YDM AND SUBSEQUENT YDM DASH NUMBERS; IRU NCD - IRUs are on but no data or bad data is transmitted.
 (q)  IRU DIFF - The yaw damper module has detected an invalid input from an inertial reference unit but is unable to determine
 which one is at fault.
 (r) (s)  LVDT - The yaw damper module has detected that the LVDT common mode voltage is low. During the preflight test, an LVDT fault is recorded if the common mode voltage is low and a position test fault is detected (valid high hydraulic pressure must be present).YD ACT - During normal operation, a yaw damper actuator fault occurs when the yaw damper module detects a servo loop fault. During the preflight test, a yaw damper actuator fault is recorded if a position test fault occurs. To record a YD ACT fault, valid high hydraulic pressure must be present and the LVDT common mode voltage must be normal.

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757 MAINTENANCE MANUAL
 (t)  
AIRPLANES WITH -124 YDM AND SUBSEQUENT YDM DASH NUMBERS; YD TEST - Failure of PFT (Pre-Flight Test).

 (u)  
YDM - A yaw damper module fault is recorded and latched with the following faults: power up test fault, preflight test fault, A/C type code input fault, control or monitor channel command coincidence fault, or a computing channel fault. A YDM fault is also recorded when either control or monitor channel detected auto-disengage relay faults.

 (v)  
AIRPLANES WITH MODAL SUPPRESSION ACCELEROMETER; YDM fault is also shown when there is a loss of excitation voltage for the accelerometer. 1) If no YDM fault exists, the YDM fault latch resets for the

 following conditions: a) Successful completion of power up test or maintenance reset on ground. b) Power up reset, manual engage or YDM autoreset in air or on ground.
 (7)  
Fault messages are displayed on the 12 character alphanumeric LED display located on the faceplate of the yaw damper module. To view the fault messages, the DISPLAY button is pressed on the faceplate of the yaw damper module until all the fault messages are displayed. To display the fault messages one at a time, the DISPLAY button is pressed and released to display each message. The fault messages automatically extinguish from the display after 30 seconds. LAST LEG FAULT messages are distinguished from FAULTS NOW messages by an asterick (*) preceeding the fault message. To view the first fault message, the DISPLAY button is pressed and held for over 2 seconds.
　
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