DATA BUS NO. 4
OUTPUT

SAME AS
-15V DC
M7953 -15V DC
DISTR
A
B164 ADC-R (E2-3)
M7955 MODAL SUPPRESSION ACCEL-L
|15V DC +15V DCAFT (STA 2260, WL 194, LBL 65)
-15V DC
OUTPUT
+5V DC 2
LOWER YDM+5V DC
2 DATA BUS NO. 1
DATA BUS NO. 3
OUTPUT
C POWER TO
B7161 IRU-L (E1-6)
MONITOR .P  B7163 IRU-C (E1-6)
+5V DC
2
OUTPUT

DATA BUS NO. 2 PWR UP
B7162 IRU-R (E1-6)
PSM VALIDRESETTO MONITORS PSM RESET
M7358 FCE PWR SPLY 1L (E1-2)
AIR

AIR/GND 1 +15V DCAIR/GND 1/2
|15V DC
D
OUTPUT-15V DC SIGNAL GND
AIR/GND 2GND
+5V DCLOGIC GND
RXXX FCE AIR/GND+15V DC
OUTPUT RELAYS (TYP 3 PLACES)
POWER-15V DC
DISTR
+15V DC
|15V DC
B
OUTPUT -15V DC +5V DC PSM VALID POWER TO
CONTROL .P
PSM RESET
WW
INSTRUMENT
+5V DC

LIGHTING
OUTPUT

OFF
E 3
28V DCON
STBY BUS
C8780MASTER DIMM7359 FCE PWR SPLY 2L (E1-2) M7362 YAW DAMPER MODULE-UPPER YAW DAMPER AND TEST
AA
(E1-2)
UPPER NOTES:A P7-1 CB PNL ASSY INOP 1
IMPACT PRESS., AOA, TAS (SHT 2)
(S2) YAW DAMPER UPPER2
ROLL RATE, ROLL ATT, YAW RATE,
LAT ACCEL, GND SPEED M7315 (YMY) PASSENGER OXYGEN ANDYAW DAMPER CONTROL PANEL (P5)
Yaw Damper - Upper Schematic
Figure 8 (Sheet 1)

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M7353 EIU-L (E1-5) M7362 YAW DAMPER MODULE-UPPER (E1-2)
Yaw Damper - Upper SchematicFigure 8 (Sheet 2)
Page 27Feb 18/02
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MAINTENANCE MANUAL

 c)  The comparison monitor provides a VALID HI HYDRAULIC PRESS discrete signal and a HYD PRESS reset when high pressure is restored for 6 seconds after a low pressure indication.
 4) Air/Ground Relays a) Air/ground information is received on three status lines from the air/ground relays. The status lines indicate: right gear aft tilt switch level (airplane on ground - through master A/G relay), right gear aft tilt switch level (airplane on ground - direct to YDM), and right gear forward tilt switch level (airplane on ground - direct to YDM). b) A triplex majority vote signal selector/monitor is used to determine A/G status. The monitor detects when one of three previously valid inputs is different from the selected value for more than 2 seconds. When the two remaining valid inputs disagree for more than 2 seconds following a first failure, a second failure is detected.
 5) ADC a) The ADC parameter values for overspeed, impact pressure, indicated angle of attack, and true airspeed are received on the ARINC 429 data bus. Input signal monitoring provides continuous active monitoring for both primary and secondary ADC inputs. Excessive signal failure rates or lack of activity result in an ADC input fault. b) A median value for each parameter is selected for use in the control law. Incoming parameter values are compared with the median value and are fault registered if the comparison is beyond the maximum limits.
 6) IRU a) The IRU parameter values for roll rate, roll attitude, yaw rate, lateral acceleration and ground speed are received on the ARINC 429 data bus. Input signal monitoring provides continuous active monitoring for the left, right, and center IRU inputs. Excessive failure rates or lack of activity results in an IRU input fault.
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747-400 MAINTENANCE MANUAL
 b)  A median value for each parameter is selected for use in the control law. Incoming parameter values are compared with the median value and are registered as faults if the comparison is beyond the maximum limits.
 7)  Power Supply Modules (PSMs)
 a)  The FCE PSMs (No. 1 and 2 left) each furnish PSM reset and PSM valid signals. The PSM reset will have a valid low state when the 115-volt ac power input to the PSM is removed or interrupted.
 (c) Computing Channels 1) Each yaw damper module consists of two independent microprocessors with dissimilar software and instruction sets. Each microprocessor and associated software form a separate computing channel. They are a MONITOR channel and a CONTROL channel. Each microprocessor is programmed with the following software functions: a) Executive b) Power-up test and actuator ground test c) Input, output, and initialization d) Foreground software that includes input monitors, signal selectors, redundancy management, comparison monitors, degraded mode logic, control laws, and annunciation logic. e) Background monitors that conduct watchdog monitor tests and Read Only Memory (ROM) tests. 2) Control Law Computations a) The APL type code ensures that the software in the module is correct for the airplane in which it is installed. The control law continually computes output commands. The output is zero on the ground (except during the ground test) due to the disabled easy-on/easy-off function.
　
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