TM  1-1520-240-10            3-4-3 3-4-3.  Normal Operation — Transponder System. The following steps provide transponder system operat- ing procedures. a.  Starting. (1) Move  the  MASTER  switch  from  OFF  to STBY.  If  the  aircraft  is  so  equipped,  observe  that  the STBY light on the aircraft advisory panel comes on. Also, note that the NO GO light is on. (2) Allow 2 minutes for warmup. (3) Select the codes assigned for use in modes 1 and 3/A by depressing and releasing the pushbutton for each switch until the desired number shows. (4) Operate  the  PRESS-TO-TEST  feature  of the lamp indicators. (5) Place the ANT switch BOT. (6) Move  the  MASTER  switch  from  STBY  to NORM. (7) Hold the M-11 switch to TEST, observe that the TEST/GO indicator lights. (8) Restore the M-1 switch to ON. (9) Repeat (7) and (8) above for the M-2, M-3/A and M-C mode switches. (10)   Place the ANT switch TOP. (11)    Repeat (7), (8), and (9) above. (12)   Place the ANT switch DIV. (13)   Repeat (7), (8), and (9) above. NOTE If KIT1C is not installed or keyed the following steps are not required. (14)   Set the MODE 4 rotary switch to A. If the external computer is used, set a code in it. (15)   Set the MODE 4 AUDIO/LIGHT/OUT switch to OUT. (16)   Hold the MODE 4 TEST/ON/OUT switch to TEST.b. (1) If  the  computer  is  used,  observe  that  the TEST  GO  indicator  lights.  If  the  computer  is  not  con- nected, observe that the TEST/MON/NO GO indicator lights and the KIT STATUS indicator lights. (2) Observe that the MODE 4 REPLY light and CAUTION light (on a separate “panel”) do not light. (3) Restore the MODE 4 TEST/ON/OUT switch to  ON  for  computer  use,  or  to  OUT  if  no  computer  is used. c.  Stopping. (1) If code retention is desired: (a) MODE   4   CODE   selector   switch   — HOLD, then release. (b) MODE 4 CODE selector switch — A or B, as applicable. (c) MASTER control switch — OFF. (2) If code retention is not desired: (a) MODE   4   CODE   selector   switch   — ZERO. (b) MODE 4 CODE selector switch — A or B, as applicable. (c) MASTER control switch — OFF. d.  Turn KYK-13 Mode switch to OFF. e.  Disconnect KYK-13 from aircraft receptacle. Figure  3-4-1.  AN/APX-100 Control Panel 3-4-4.  GPS Zeroize Switch.  (fig. 2-1-8) The GPS Zeroize switch is located on center instrument panel,  right  side  of  AN/APR-39AV(1)  Indicator,  and  is used to erase any crypto data and all navigational infor- mation stored in the GPS Receiver. This zeroize switch consists of a guarded toggle switch. 3-4-5.  Normal Operation - GPS Zeroize Switch. NOTE Aircraft battery must be connected, or power applied to aircraft. a.  Lift  protective  guard  from  zeroize  toggle  switch and activate switch. b.  If GPS receiver is on, turn Data Switch to Stat. Observe message on Page 1, Line 2.