TM 1-1510-218-10 3C-10 NOTE If   two   short   800-Hz   tones   are   heard,   the transceiver  has  detected  an  internal  fault.   Push  the  TEST  button  on  the  transceiver control  unit  to  initiate  self-test and display the fault code. Adjust  the  volume  and  perform  a  quick  squelch test  by  setting  the  power  and  mode  switch  on  the transceiver  control  unit  to   SQ  OFF  and  adjusting  the volume    level    with    background    noise.        After    a comfortable    listening    level    has    been    established, return the power and mode switch to the  ON position.   AU   background    noise   should   disappear   unless   a station    or    aircraft    is    transmitting    on    the    active frequency the fault code. (2)   Frequency Selection. Frequency selection  is  made  using  either  the  frequency  select knobs, or the XF / MEM recall switch. NOTE There    is    usually    an    installer    supplied 8.33/25   kHz   select   switch   in   the   cockpit.   This switch provides a convenience to the pilots  by  not  having  to  "ratchet  pass"  the 8.33  kHz  channels  when  not  operating  in 8.33 airspace.  The selected position of the (8.33 or 25) may or may not be annunciated, depending on installation. After the desired frequency is set into the preset frequency  display,  it  can  be  transferred  to  the  active frequency   display   by   momentarily   setting   the   XF  / MEM switch to  XF.  At the same time that the preset frequency   is   transferred   to   the   active   display,   the previously active frequency is transferred to the preset display.    A  short  audio  tone  is  applied  to  the  audio system to indicate that the active frequency has been changed,   and   the   active  (ACT)   annunciator   on  the control will flash while the transceiver is tuning to the new frequency. NOTE The  ACT  annunciator  continuing  to  flash indicates  that  the  transceiver  is  not  tuned to  the  frequency  displayed  in  the  active display. The   transceiver   control   unit's   memory  permits storing  up  to  six  preset  frequencies.    Once  stored, these frequencies can be recalled to the preset display by   positioning   the   XF   /   MEM   switch   to   the   MEM  position.      The   storage   location   (CHAN   1   through CHAN 6) for the recalled frequency is displayed in the active frequency display while the  XF / MEM switch is held in the   MEM  position.    All  six  stored  frequencies can be displayed one at a time in the preset display by repeatedly   positioning   the   XF   /   MEM   switch   to   the MEM  position.  After the desired stored frequency has been    recalled    to    the    preset    display,    it    can    be transferred    to    the    active    display    by    momentarily positioning the XF / MEM switch to the XF position. During normal operation, all frequency selections and revisions are done in the preset frequency display.   However, the active frequency can be selected directly as described in the following paragraph. (3)   Direct  Active  Frequency  Selection.    The active   frequency   can   be   selected   directly   with   the frequency select knobs by pushing the  ACT button for about   2   seconds.      The   active   frequency   selection mode  is  indicated  by  dashes  appearing  in  the  preset display.    Also,  the   ACT  annunciator  will  flash  as  the frequency select knobs are turned to indicate that the transceiver is being returned. NOTE The  ACT  annunciator  continuing  to  flash after    the    frequency    has    been    selected indicates  that  the  transceiver  is  not  tuned to  the  frequency  displayed  in  the  active display. To   return   to   the   preset   frequency   selection mode,     push     the     ACT     button     again     for     about 2 seconds.  As a safety feature, the transceiver control unit  switches  to  the  active  frequency  selection  mode when  a  frequency  select  knob  is  operated  while  the STO   and   TEST  buttons,  or    XF   /   MEM  switch  are actuated. (4)   Frequency   Storage.      To   program   the memory, select the frequency in the preset frequency display using the frequency select knobs and push the STO   button   once.      One   of   the   channel   numbers (CHAN 1  through  CHAN  6)  will  appear  in  the  active display for approximately 5 seconds.  During this time the channel number can be changed without changing the  preset  frequency  by  momentarily  positioning  the XF   /   MEM   switch   to   the   MEM  position.    After  the desired channel number has been selected, push the STO button again to store the frequency.