TM  55-1510-221-10 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. MODE  1  code  selectors  -  Set  (if applicable). MODE 3/A code selectors - Set (if applicable). MODE  4  code  control  -  Set  (if required). MODE  4  REPLY  indicator  - Monitor   to   determine   when   tran- sponder   set   is   replying   to   a   SIF interrogation. MODE  4  AUDIO  OUT  switch  - Set  (as  required  to  monitor  Mode 4  interrogations  and  replies). MODE  4  audio  and/or  indicator  - Listen  and/or  observe  (for  Mode  4 interrogations   and   replies). IDENT-MIC-OUT   switch   -   Press to   IDENT   momentarily. MODE   4   TEST-ON-OUT   switch - TEST. Observe  that  the  TEST  GO  indi- cator   light   illuminates. MODE   4   TEST-ON-OUT   switch - ON. ANT  switch  -  BOT. Repeat  steps  4,  5,  and  6.  Observe that  the  TEST  GO  indicator  illu- minates. TOP-DIV-BOT-ANT   switch   - TOP. Repeat  step  14. TOP-DIV-BOT-ANT   switch   - DIV. Repeat  step  14. When  possible,  obtain  the  cooper- ation  of  an  interrogating  station to  exercise  the  TEST  mode.  Exe- cute  the  following  steps: a. RAD  TEST-OUT  switch  - RAD  TEST. b.  Obtain  verification  from interrogating   station   that   a TEST  MODE  reply  was received. c. RAD  TEST-OUT  switch  - OUT. (4.)  Transponder  set  identification-position d.   Transponder   -   Emergency   Operation.   Not operating  procedure:  The  transponder  set  can  make applicable. identification-position  replies  while  operating  in code  Modes  1,  2,  and/or  3/A,  in  response  to  ground station  interrogations.  This  type  of  operation  is  initi- ated  by  the  operator  as  follows: 1. Modes  1,  2,  and/or  3/A  -  ON,  as required. 2.   IDENT-OUT-MIC   switch   -   Press momentarily   to   IDENT,   when directed. NOTE Holding   circuits   within   the   transponder receiver-transmitter   will   transmit   identifi- cation-position   signals   for   15   to   30   sec- onds.  This  is  normally  sufficient  time  for ground  control  to  identify  the  aircraft’s position.  During  the  15  to  30  second period,  it  is  normal  procedure  to  acknowl- edge   via   the   aircraft   communications   set that   identification-   position   signals   are being   generated. NOTE Set  any  of  the  M1,  M2,  M3/A,  M-C,  or MODE   4   switches   to   OUT   to   inhibit transmission   of   replies   in   undesired modes. NOTE With  the  IDENT-OUT-MIC  switch  set  to the   MIC   position,   the   POS   IDENT   but- ton  must  be  depressed  to  transmit  identi- fication  pulses. (5.)   Shutdown   procedure: 1. To  retain  Mode  4  code  in  external computer   during   a   temporary shutdown: a. MODE   4   CODE   switch   - Rotate  to  HOLD. b.  Wait  15  seconds. c. MASTER  control  -  OFF. 2. To zeroize the Mode 4 code in the external   computer   turn   MODE   4 CODE  switch  to  ZERO. 3. MASTER control - OFF. This will automatically   zeroize   the   external computer  unless  codes  have  been retained  (step  1  above). 3-82