1)  The fault mode is entered as a result of the following: a) Failure of the power-up test
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 b) Failure of the preflight test c) INOP type failure resulting in automatic disengagement
 2)  AIRPLANES WITH YDM DASH NUMBERS -101 THRU -121; When the fault mode is entered, the associated channel is disengaged, the INOP lamp is illuminated, and the affected faultballs are set.
 3)  AIRPLANES WITH -122 YDM AND SUBSEQUENT YDM DASH NUMBERS; When the fault mode is entered, the associated channel is disengaged, the INOP lamp is illuminated, and the corresponding fault message is recorded.
 4)  The fault mode exits to the power up mode by a maintenance reset, or to the ground operational mode by automatic re-engagement if no INOP faults remain.
 (3) Yaw Damper Schematic (Fig. 8)
 (a) Electrical Power
 1)  Yaw damper module operating power consists of +5 and |15 vdc parallel inputs from CSEU power supply modules 1L and 2L.
 2)  AIRPLANES WITH YDM DASH NUMBERS -101 THRU -121; Two parallel inputs from the CSEU circuit breakers supply the 28 vdc used to drive the fault ball indicators.
 3)  The 28 vdc engage solenoid power is supplied by a YAW DAMPER circuit breaker via the ON switch. The 26 vac, 400 Hz servo LVDT excitation is supplied by the CSEU power supply modules.
 (b) Inputs
 1)  AIRPLANES WITH YDM DASH NUMBERS -101 THRU -121; Airplane Type Code a) The airplane type code is a three-wire ground
 combination with a fourth wire for parity.
 b)  The parity monitor checks parity and compares type code with the software issue code. This ensures that the correct software is used for the airplane type in which the yaw damper module is installed. If installed correctly, an APL TYPE VALID signal is issued. A detected failure disengages the yaw damper, illuminates the INOP light, provides an EICAS yaw damper message, and sets the YDM faultball.
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OUTPUT
28V DC

+28V DC POWER
BUS NO. 1STBY BUS CSEU POWER
FLT CONT
RIGHT YAWELEC 1L-DCA
SUPPLY
DAMPER MODULE RIGHT AIR DATA CMPTR1 MODULE
OUTPUT FLT CONT BUS NO. 1ELEC 2L-DC LEFT AIR DATA CMPTRP11
P OTHER
SIGNAL (|15V) GND
LOGIC (|5V) GND
1700 PSI CSEU +5V DC
MODULES
POWER  HYDRAULIC PRESSURE
B
SUPPLY  SWITCH+5V DC A DATA BUS 3OUTPUT IRU SELF TEST RIGHT YAW+15V DC
DAMPER OUTPUT|15V DC +15V DC RIGHT IRU MODULE
-15V DC
-15V DC
POWER PSM 1 VALID

CSUPPLY
DATA BUS 3
POWER UP
RIGHT YAW
MODULE

IRU SELF TEST
PSM 2 VALIDRESET TO
DAMPER
VALID

MONITORS
PSM 1 RESET

MODULE
CENTER IRU
AND DATA BUS 3
FAULTBALLS IRU SELF TEST
POWER PSM 2 RESET
SUPPLY
MODULE
RESET

LEFT IRU
+5V DC
DOUTPUT
RIGHT YAW DAMPER MODULE
|15V DC

+15V DC E OUTPUT
-15V DC
AIR CSEU POWER SUPPLYMODULE 1 L
AIRTEST PANEL
GND GND
AIR/GND SYS AIR/GND SYSNO. 2 RELAY
AIRNO. 1 RELAY +5V DC GND F
OTHEROUTPUT CSEU AIR/GND SYS MODULES
AIR NO. 1 RELAY|15V DC
+15V DC
OUTPUT

-15V DC GND POWER
AIR/GND SYS
SUPPLY
NO. 2 RELAY
MODULE OFF WW
VALID INSTRUMENT LIGHTINGPOWER
28V DC
G
SUPPLY
STBY BUS
INOP
MODULE
L-YAW

RIGHT YAW
RESET +5V DC DAMPER
DAMPER
OUTPUT +5V DC MODULE
ENGAGE
P11-1
H |15V DC -15V DC
+15V DC
POWER AA |15V DC SUPPLY MASTER DIM
OUTPUT -15V DC B AND TEST
SIGNAL (|15V) GND INOP
LOGIC (+5V) GNDMODULE 2 LCSEU POWER SUPPLY
LEFT YAW DAMPER
PRESSURE RETURN

FLIGHT CONTROL PNLN0TE: TYPICAL SYSTEM (LEFT SIDE SHOWN)
LEFT YAW DAMPER
　
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