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 The maintenance flag does not actuate when the system is in
 fast synchronization mode.
 (10) INS Valid Sensor
 (a) If an INS platform heading valid signal is not present at the
 INS valid sensor, (sheet 1, Fig. 5) fast synchronization
 cannot be initiated and the superflag output will be invalid.
 The maintenance flag does not actuate under this condition.
 (11) SET HDG Knob Function
 (a) The set heading control (Sheet 1, Fig. 5) is controlled by
 the SET HDG knob on the compass controller. Since the set
 heading control is not disabled in the SLAVED mode, the SET HDG
 knob may be used to check slaving. When the SET HDG knob is
 rotated to any position other than center, a signal is applied
 through the set heading control to increase the excitation
 voltage to the stepper motor and to cause the superflag output
 to be invalid. The rate at which the stepper motor will rotate
 (set heading rate) is controlled by the signal which is applied
 to the frequency control and limiter.
 (b) When the SET HDG knob is in the first clockwise or counter-
clockwise position, the heading output will change at a rate
 of 40 to 80 degrees per minute. When the SET HDG knob is at
 either extreme clockwise or counterclockwise position, the
 heading output will change at a rate of 800 to 1200 degrees
 per minute. The direction of rotation is controlled by the
 position of the SET HDG knob from center.
 (c) The SET HDG knob is spring loaded to the center (off)
 position. In SLAVED mode, after the SET HDG knob is released
 the system will synchronize back to the airplane magnetic
 heading at a rate of 1 to 2 degrees per minute.
 C.  Functional Description, DG mode

 EFFECTIVITY

 

 ALL  ATG Page 31  Apr 25/8734-21-00

 (1)  
The MHRS operates in the DG mode when the COMPASS switch on the compass controller (Sheet 1, Fig. 5) is placed in the DG position. In this mode, the slaving circuits which control the stepper motor are turned off. The system follows the changes of the heading information from the INS platform. In this mode the output synchros can be set to any desired heading by using the SET HDG control on the compass controller.

 (2)  
Magnetic Field Sensor

 (a)  The magnetic field sensor input is not used in the DG mode. The magnetic heading error signal from the heading error amplifier is disabled by the DG mode input to the frequency control and limiter. In the DG mode the output of the SLAVED/DG control disables the magnetic field sensor excitation monitor, the annunciator, and the slaving circuit.

 (3)  
Superflag Control

 (a)  The operation of the superflag control is the same in the DG mode as in the SLAVED mode, except that when magnetic field sensor excitation is lost, the superflag output will remain valid.

 (4)  
SET HDG Knob Function

 (a)  The heading outputs of the control transmitters are controlled by the SET HDG knob on the compass controller and the inertial platform signal. The control information supplied by the SET HDG knob in the DG mode is the same as that supplied in the SLAVED mode, except that when the SET HDG knob is released, the heading will remain at the set position until the airplane changes heading. When the airplane changes heading, the servo loop will position itself to the relative heading change.

 D. Controls
 (1)  
Prior to operating the magnetic heading reference system, electrical power must be provided to the airplane (Ref 24-22-00). The STANDBY IGNITION switch must be in NORM position and both VOR/ILS-INS switches must be in the VOR/ILS position. All flight instrument switching must be in the normal position and instrument panel lighting should be adjusted for optimum intensity.

 (2)  
Inertial navigation systems No. 1 and 2 must be on and operating in NAV mode with present position inserted. Main power, platform heading, and HSI circuit breakers must be closed (Ref 34-41-00, Adjustment/Test.

 (3)  
The STBY IGN and MHRS circuit breakers on main circuit breaker panel (P6) must be closed. The MHRS, RMI, HDG SYNC EXCIT, and FLT INST SW RELAYS circuit breakers on the electronic circuit breaker panel (P7) must be closed.

 EFFECTIVITY

 

 ALL  01 Page 34  Apr 25/8734-21-00
 MAGNETIC HEADING REFERENCE SYSTEM - TROUBLE SHOOTING
____________________________________________________

 1.  General
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