TM   55-1520-240-T 18-3.3   DOPPLER/GPS   NAVIGATION   SYSTEM   OPERATIONAL   CHECK 18-3.3 INITIAL  SETUP Applicable    Configurations: All References: TM  11-1520-240-23 TM  11-5841-305-12 TM   55-1520-240-23 Tools: Electrical Repairer’s Tool Kit, NSN   5180-00-323-4915 Materials: None Personnel   Required: Aircraft Electrician (2) Equipment   Condition: TM   55-1520-240-23: Battery  Connected Electrical Power Off Hydraulic  Power  Off Doppler/GPS  Navigation  System  Visual Check  Performed (Task  18-3.2) NOTE TASK RESULT NOTE Remove aircraft from overhead cover. CHECK   CIRCUIT   BREAKERS 1. 2. Check that DOPPLER breakers (1) on No. 1 and 2 pdp are closed. If circuit breakers are open, close them. Start  APU.  Refer to task 15-1.4. APU ON capsule shall come on. CHECK  DGNS  LIGHTING 3. Turn aircraft CTR CSL LTG control (2) clock- wise  and  counterclockwise  while  checking CDU (3) Edge lighting is illuminated and all keyboard  keys  are  illuminated. 4. Set CDU (3) MODE switch (4) to LAMP TEST. CDU MAL LAMP and all LED segments on four-line Enter GPS mode “M”. Verify that MAL LAMP display are illuminated. If CDU MAL LAMP and all LED and ail LED segments on four-line display are segments are not illuminated go to task illuminated. 18-3.5. 5. Press CDU (3) DIM (5) pushbutton several times, the BRT (6) pushbutton several times. CDU (3) panel Edge light and all keyboard lights shall vary with the changing setting of the aircraft dimmer control  (2).  If  CDU  (3)  panel  Edge  and  keyboard  lights are not visible or intensity level does not vary with air- craft dimmer control (2) go to task 18-3.4 The LED display will grow dimmer then brighten. If the intensity of the LED display does not vary replace CDU. TASK RESULT 6. Set CDU (3) MODE switch (4) to TEST. After Doppler and/or GPS self tests have been com- pleted (approximately 15 seconds for Doppler, up to 2 minutes for GPS) one of the following indications will be observed in left and right displays. If the display is not GO ALL go to task 18-3.6. In the event TEST mode display is not GO ALL the system should be recycled through OFF to verify that the failure is not momentary one. LEFT  DISPLAY RIGHT  DISPLAY GO GO GO NG DN DF GN ALL P C, R, S or H fol- lowed by a nu- meric  code A failure has occurred in the Computer Display Unit or the Signal Data Con- verter Power Supply. The operator should not use the System. GPS failure code GPS has failed but operator can use Doppler to perform all navigation. Doppler  failure code Doppler has failed. GPS is still performing self test. Doppler  failure code Doppler has failed but operator can use GPS to perform all code navigation. REMARKS Doppler has completed Built In Test (BIT) and is operating satisfactorily, GPS is still performing BIT (GPS has a 2 minute BIT cycle maximum). Note that a rotating bar in the display indicates that the GPS is still performing self test. The entire system has completed BIT and is operating satisfactorily. Pitch or Roll data is missing or exceeds 90 degrees. In this case, pitch and roll in the computer are both set to zero and navigation in the Doppler mode continues with degraded operation. Problem may be in the vertical gyro or aircraft  cabling. GO  TO  NEXT  PAGE 18-70   Change   19