TM 1-1510-225-10 3-10 (18)   M-3/A TEST Switch. (a)  TEST     –    Permits    self-test    in    the selected mode. (b)  ON    –   Permits   set   to   reply   in   the selected mode. (c)  OUT –  Disables replies. (19)   M-2 Test Switch. (a)  TEST     –    Permits    self-test    in    the selected mode. (b)  ON    –   Permits   set   to   reply   in   the selected mode. (c)  OUT – Disables replies. (20)   M-1 TEST Switch. (a)  TEST     –    Permits     self-test    in    the selected mode. (b)  ON    –   Permits   set   to   reply   in   the selected mode. (c)  OUT – Disables replies. (21)   Control  Wheel  R  F3   .  An   IDENT  push button  is  located  on  the  pilot's  control  wheel.    When pressed, the transponder transmits identification reply to ground.  Refer to Figure 2-22. c.   Transponder Operations. (1)   Activation/Test  Procedure.    Perform  the following setup/test procedures each time the APX-100 transponder is activated. NOTE Do not perform any checks with the master switch   in   EMERG   or   with   M-3/A   codes 7500,  7600  or  7700  without  first  obtaining authorization from the interrogating station(s). 1.   Ensure the   MASTER  switch  is  in  the STBY position. 2.   Allow   transponder   to   warm   up   for 2 minutes before operation. 3.   Operate   the   press-to-test   feature   to the TEST indicator light to ensure light illuminates. 4.   Test each   MODE   (M-1,  M-2,  M-3/A, and  M-C)  individually  by  momentarily holding   each    MODE   switch   in   the TEST     position.          The     green     test indicator  light  should  illuminate  each time. 5.   Return    all    switches    to    the    normal operating position. (2)   Operating   Procedures.      The   Activation/ Test  Procedures  above  will  leave  the  APX-100  in  an operating   condition.      The   following   additional   steps may be required, depending upon mission instructions. NOTE If   the   external   security   computer   is   not installed  in  the  aircraft,  a  NO-GO light will illuminate  any  time  the  MODE  4  switch  is moved out of the OFF position. 1.   Change   the   MODE   4   CODE  rotary switch from  A to B. 2.   If  it  is  desired  to  retain  the   CODE in the external computer during a temporary    shutdown    for    passenger discharge     or     refueling,     rotate     the MODE  4  CODE switch to  HOLD  prior to   touchdown   and   then   release   it.   Wait  15  seconds  before  turning  the MASTER rotary switch to OFF. 3.   Dumping   the   CODE  in  the  external computer  is  accomplished  by  turning the MODE 4  CODE switch to ZERO. 4.   Set any of the  M-1,  M-2,  M-3/A,  M-C, or  MODE  4 switches to  OUT to inhibit transmission of replies in the undesired modes. 5.   Set  the   IDENT  /   OUT  /   MIC  switch momentarily   to    IDENT   in   order   to transmit   the   identification   of   position (I/P) pulses.  Placing this switch in the MIC position will allow transmission of I/P    pulses    when    either    CONTROL wheel  POS  IDENT  button  is  pressed, I/P  transmission  pulses  last  for  15  to 30 seconds. (3)   Shutdown Procedures. Rotate the MASTER switch to  OFF.   This  will  automatically  zero the  external  computer  codes  unless  they  have  been retained as in step 2 of Operating Procedure.