TM  55-1510-221-10 NOTE It  is  not  possible  to  load  displays  from  the keyboard.  A  temporary  failure  of  a numerical   key   may   prevent   data   loading. If  a  number  cannot  be  loaded  into  lati- tude  or  longitude  displays,  after  pressing/ wiggling  the  key  several  times,  the  cause may  be  the  momentary  hang-up  of another  key.  To  identify  the  faulty  key, rotate   the   data   selector   to   DSRTK/STS. The  right  digit  on  right  display  will  indi- cate  suspect  key.  Press  and  release  suspect key   several   times.   To   test   whether   the keyboard  problem  is  corrected,  try  press- ing   any   other   numerical   key.   Its   number should   now   appear   as   the   right   digit.   If this  test  is  successful,  press  the  CLEAR key  and  return  data  selector  to  original data  loading  position.  Otherwise,  a  CDU failure  is  indicated. minated. (d.) CDU  BAT  indicator  light  is  illu- Operation  on  battery  is  an  indication  that there  may  may  be  no  aircraft  power  to blower  motor  with  resultant  loss  of  cool- ing.  The  INS  can  operate  only  a  limited time   (normally   15   minutes)   on   battery power  before  a  low  voltage  shutdown  will occur.   Then,   immediate   corrective   action must  be  taken. NOTE CDU  BAT  indicator  will  illuminate  for 12  seconds  in  alignment  State  “8“  (about 5   minutes   after   turn-on).   This   is   normal and  indicates  a  battery  test  is  in  progress. No  corrective  action  is  required. NOTE During  ground  operation,  it  is  recom- mended   that   operation   on   battery   power not  exceed  5  minutes. 1. To  determine corrective action:   (Monitor   CDU   dis- plays  while rotating   the CDU  selector  switch.) a. If   displays   are   frozen (do   not   change   while data  selector  is  being rotated)  problem  is normally  in  the  naviga- tion  unit. b. If  displays  respond  nor- mally  to  the  data  selec- tor,  the  problem  is  nor- mally  absence  of  115V AC  power  to  INS. (e.)   For   corrective   action:   Check   to assure  proper  settings  of  following  switches  and  cir- cuit  breakers  essential  to  INS  operation: 1.   Overhead   circuit   breaker panel  (fig.  2-26)  -  Circuit breakers  in: a. AVIONICS  MASTER CONTR b.  INS  CONTROL c. AVIONICS  MASTER PWR  No.1 d.   AVIONICS   MASTER PWR  No.2 2.  Overhead  control  panel  (fig. 2-12):  INVERTER  No.  1  or INVERTER  No.2  switch  - ON  (either). 3.  Mission  control  panel  (fig. 4-1): a. #1    INV    or    #2    INV switch  -  ON. b.  Bus  cross  tie  switch  - ON/AUTO. 4. Mission  AC/DC  Power  Cab- inet (fig. 2-2): INS AC PWR circuit  breaker  -  In. NOTE CDU   BAT   indicator   should   extinguish after  above  corrective  action.  If  it  remains illuminated,   INS   will   eventually   shut down   when   battery   voltage   drops   below approximately 19VDC.   Flight   crew should  prepare  for  shutdown. (3.)   Malfunction   indications   and   proce- dures:  Table 3-3 details the procedure for a Malfunc- tion  Code  Check.  Table  3-4  lists  a  number  of  mal- function  indications  which  occur  under  given  modes of   operation.   Follow   procedure   given.   Table   3-5 details  action  codes  and  recommended  action.  Table 3-72