(3)  
The processed data is also provided to the ACMS (Ref 31-35-00).

 (4)  
An ATE connector and fault indicator are located on the front panel of the DFDAMU. The ATE connector is provided to connect external test equipment. The FDAU FAULT indicator comes on to indicate that the DFDAMU has detected an internal fault.

 (5)  
The DFDAMU provides 28-volt dc power for the accelerometer
 excitation.

 (6)  
The DFDAMU coding and aircraft ident shorting receptacle are located behind the DFDAMU. Access is through the partition from the forward cargo compartment.

  GUN 051 ú

 31-31-00
 ú CONFIG ú 01 Page 4 ú Dec 20/93

A

757
MAINTENANCE MANUAL

 F. Digital Flight Data Recorder (DFDR)
 (1)  
The DFDR records the data output by the DFDAMU. Data from the last 25 hours of operation is stored on 1/4-inch wide magnetic tape. The tape is located in a crash-proof container within the DFDR.

 (2)  
The DFDR is installed on the voice and flight recorder rack E7. This rack is located above the aft galley ceiling. The exterior of the DFDR is painted bright orange and has reflective tape affixed to it to aid in its location in the event of an accident.

 (3)  
The front panel of the DFDR contains a BITE indicator and a copy recorder connector. An underwater locator beacon is installed on the front panel. The indicator is black when the DFDR is operating properly. The BITE indicator turns yellow when a fault is detected in the DFDR or power is off to the unit. The copy recorder connector allows the recorded data to be transferred to separate copy recorder.

 (4)  
The underwater locator beacon (ULB) aids in location of a submerged DFDR by sending out an acoustic signal when the unit is submerged in water.

 (5)  
The ULB is contained in a cylindrical watertight case designed to withstand high impact shock and deep water immersion. It is mounted on the front panel of the DFDR.

 (6)  
The ULB is battery operated and is designed to operate for at least 30 days when immersed. It will withstand water depths of 20,000 feet and has a maximum detection range of 2,000 to 4,000 yards.

 3. Operation
_________
 A. Functional Description (Fig. 2)
 (1)  Power Distribution and Control
 (a)  
During normal operation, ac power is supplied to the flight recorder system through the left and right ENG START-TO-STOP relays. The relays are wired in parallel so that any one relay can provide power to the system.

 (b)  
The left and right ENG START-TO-STOP relays are actuated when the corresponding engine is first started. The engine ignition switches control the operation. At engine start, when an engine ignition switch is first turned on, the corresponding ENG START-TO-STOP relay (left or right) is energized. After the fuel control switch is set to RUN, it will cause the flight recorder control relay to remain energized after the ignition switch is selected to OFF. The relays remain energized until the fuel control switches are set to CUTOFF.
　
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