TM 1-1510-224-10 4. Power and mode switch (fig. 3-25)  - ON. After  power  is  applied,  the  control  unit  displays the    same    active    and    preset    frequencies    that    were present when the equipment was last turned off. (2)   Frequency selection. Frequency selection   is   made   using   either   the   frequency   select knobs, or the  XFR/MEM (transfer/memory recall switch). Rotation   of   either   frequency   select   knob   increases   or decreases the frequency in the preset frequency display. The  larger,  outer  knob  changes  the  frequency  in  1-MHz increments  (number  to  the  left  of  decimal  point).    The smaller,  inner  knob  changes  the  frequency  in  0.05  MHz increments.    After  the  desired  frequency  is  set  in  the preset   frequency   display,   it   can   be   transferred   to   the active   frequency   display   by   momentarily   setting   the XFR/MEM  switch  to   XFR.    At  the  same  time  that  the preset  frequency  is  transferred  to  the  active  display,  the previously  active  frequency  is  transferred  to  the  preset display.  The ACT annunciator on the control unit flashes while the receiver is tuning to the new frequency. NOTE The    ACT    annunciator    continuing    flashing indicates that the receiver is not tuned to the frequency displayed in the active display. The control unit has memory that permits storing up   to   four   preset   frequencies.      Once   stored,   these frequencies   can   be   recalled   to   the   preset   display   by positioning the   XFR/MEM  switch  to  the   MEM  position. The   storage   location   ( CH   1   through    CH   4 )    for    the recalled  frequency  is  displayed  in  the  active  frequency display while the   XFR/MEM  switch  is  held  in  the   MEM position.    All  four  stored  frequencies  can  be  displayed one    at    a    time    in    the    preset    display    by    repeatedly positioning the   XFR/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  XFR/MEM switch to the XFR position. During normal operation, all frequency selections  and  revisions  are  accomplished  in  the  preset frequency  display.    However,  the  active  frequency  can be   selected   directly   as   described   in   the   direct   active frequency selection paragraph. (3)   Direct  active  frequency  selection.    The active    frequency    can    be    selected    directly    with    the frequency  select  knobs  by  pushing  the   ACT  switch  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  receiver  is being retuned. NOTE The    ACT    annunciator    continuing    flashing indicates that the receiver is not tuned to the frequency displayed in the active display. To    return    to    the    preset    frequency    selection mode, push the  ACT  switch  again  for  about  2  seconds. As    a    safety    feature,    the    control    unit    automatically switches to the active frequency selection mode when a frequency select knob is operated while the  STO,  TEST, or XFR/MEM switches are actuated. (4)   Frequency  storage.    Up  to  four  preset frequencies  can  be  stored  in  memory  in  the  control  unit for  future  recall.    To  program  the  memory,  select  the frequency   in   the   preset   frequency   display   using   the frequency select knobs and push the   STO  switch  once. One  of  the  channel  numbers  (CH  1 through   CH  4)  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   XFR/MEM  switch  to  the   MEM  position. After   the   desired   channel   number   has   been   selected, push the STO switch again to store the frequency. NOTE When     storing     a     frequency     the     second actuation  of  the  STO  switch  must  be  done within  5  seconds  after  selecting  the  channel number or the first actuation of the STO STO switch.    If  more  than  5  seconds  elapse,  the control   will   revert   to   the   normal   modes   of operation   and   the   second   store   command will be interpreted as the first store command. After a frequency has been stored in memory, it will remain there until changed by using the  STO switch. Memory  is  retained  even  when  the  unit  is  turned  off  for an extended period of time. d. Self-Test.        During    self-test,    the    VIR-32 provides   VOR,   ILS,   and   marker   beacon   test   outputs. The     following     paragraphs     provide     the     procedures required and the results to be expected when performing the self-test. (1)   VOR Self-Test 1. Tuning   knobs   (NAV   control   unit)  - Select a VOR frequency. NOTE A   specific   frequency   is   not   required   for   the   test. Also, a signal on the frequency will not interfere with the self-test. 2. VOR/localizer    pushbutton    selector switch  (display  controller,  fig.  3-8)    - Select VOR1 or VOR2, as required. 3-59