TM 1-1510-224-10 3. Single-needle bearing pointer source selector switch (display controller, fig. 3-8)  - VOR1. 4. Double-needle bearing pointer source selector switch (display controller, fig. 3-8)  - VOR2. 5. Course   knob   (HSI)      -   Rotate   until course pointer indicates approximately 0 degrees. 6. TEST  switch  (NAV  control   unit)     - Depress and hold. 7. NAV  flag  on  the  HSI  will  come  into view. After approximately 2 seconds  the  flag  will  go  out  of  view, the   HIS   course   deviation   bar   will approximately    center,    and    a    TO indication   will   appear.   The   bearing pointers   will   indicate   approximately a  0-degree  magnetic  bearing.    The VIR-32 will return to normal operation     after     approximately     15 seconds, even if the  TEST switch is held. (2)    ILS  (Localizer  and  Glide  Slope)    Self- Test. 1. Tuning  knobs  (NAV  control  unit)    - Select a localizer 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. TEST  switch  (NAV  control   unit)     - Depress and hold. 3. HSI   -    NAV   and   GS   (glide   slope) flags    will    come    into    view.        After approximately  3  seconds,  the  flags will  go  out  of  view,  the  HSI  course deviation bar will deflect right approximately  2/3  of  full  scale  and the   glide   slope   pointer   will   deflect down approximately 2/3 of full scale. 4. The    VIR-32    will    return    to    normal operation     after     approximately     15 seconds, even if the  TEST switch is held. (3)   Marker   beacon   self-test.      The   marker beacon  assembly  is  tested  automatically  when  the  self- test is actuated and either a VOR or localizer frequency is   selected.      Proper   operation   of   the   marker   beacon assembly  is  indicated  when  all  three  marker  indicators are  displayed  on  the  EADI.    A  30  Hz  tone  will  also  be present in the marker beacon audio output. e. Marker beacon audio.  Marker beacon audio generally    associated    with    an    ILS,    must    be    source selected  by  the   NAV  A or    B   audio   selector   switches located  on  the  audio  control  panel.    Sensitivity  selection for  marker  beacon  audio  is  accomplished  by  a  toggle switch placarded MKR BCN HI-LO,  and  audio  volume  is controlled by a knob placarded  VOL (both are located on the pedestal extension, fig. 2-14). f. Diagnostic display. NOTE The  diagnostic  routines  are  intended  as  an extension   of   the   self-test   capability.      The pilot    should    first    observe    the    deviation indicators    and    associated    flags    for    the proper     self-test     responses.          If     a     fault condition exists, the problem may be verified in more detail by the diagnostics. An  extensive  self-test  diagnostic  routine  is  also initiated   in   the   VIR-32   NAV   receiver   by   pushing   the TEST switch on the  NAV control unit.  The  NAV  control unit will modulate the active and preset display intensity from minimum to maximum to annunciate the self-test is in progress.  If a fault condition existed prior to actuating self-test, the  NAV  control  unit  will  display  the  diagnostic code    associated    with    the    fault    for    approximately    2 seconds  immediately  after  the   TEST  switch  is  pressed (the  code  will  appear  in  the  preset  display).    If  a  fault  is detected   during   self-test,   that   fault   code   will   also   be displayed  on  the  NAV  control  unit  along  with  the  word ‘DIAG',   'FLAG',   or   four   dashes   ('----'):    in    the    active display.  The four dashes will be displayed along with the code   '00'   indicating   that   no   faults   have   been   found. 'FLAG’  will  be  displayed  along  with  a  2-digit  code  when something  is  abnormal  but  a  failure  has  not  occurred (i.e.    low  signal  level,  etc).    'DIAG’  is  displayed  along with a code to indicate a failure has been detected in the VIR-32.    Completion  of  self-test  is  indicated  when  either the    normal    frequency    displays    or    a    fault    code    is displayed on the NAV control.  A partial list of diagnostic and  fault  codes  is  provided  in  table  3-7.    (The   TEST switch  must  be  pushed  before  any  fault  code  can  be displayed.) 3-25. ADF RECEIVER (ADF-60). a. Introduction.    The  ADF  receiver  (fig.  3-25), provides   aural   reception   of   signals   from   a   selected ground   station   and   indicates   relative   bearing   to   that station.  The ground station must be within the frequency range of 190 to 1749.5 kHz.  The ADF receiver has three functional   modes   of   operation.      In   the   antenna  (ANT) mode  the  ADF  receiver  functions  as  an  aural  receiver, providing only an aural output of the received signal.  In automatic direction 3-60