TM 1-1510-223-10 3-60            An extensive self-test diagnostic routine is also initi- ated 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 sec- onds immediately after the TEST switch is pressed (the code will appear in the preset display). If a fault is de- tected during self-test, that fault code will also be dis- played  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, 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 be- low. The codes are listed in table 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),  pro- vides 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 finder (ADF) mode it functions as an automatic direction finder receiver in which relative bearing to the station is presented  on  an  associated  bearing  indicator,  and  an aural output of the received signal is provided. The tone (TONE)  mode  provides  a  1000-Hz  aural  output  tone when a signal is being received to identify keyed continu- ous wave (CW) signals. The ADF receiver is powered through a 2-ampere circuit breaker placarded ADF, lo- cated on the overhead circuit breaker panel (fig. 2-7). b.   ADF Control Unit Operating Controls, Indicators, and Functions. All operating controls for the ADF receiv- er are located on the ADF control unit (fig. 3-25). (1)    Active frequency display. The active frequen- cy (frequency to which the ADF receiver is tuned) and diagnostic messages are displayed in the upper window. (2)    Transfer/memory   switch.   This   switch   is   a 3-position spring-loaded toggle switch placarded XFR/ MEM, which, when held to the XFR position, causes the preset frequency to be transferred up to the active dis- play and the ADF receiver to be returned. The previously active frequency will become the new preset frequency and  will  be  displayed  in  the  lower  window.  When  this switch  is  held  to  the  MEM  position,  one  of  the  four stacked memory frequencies will be loaded into the pre- set   display.   Successive   pushes   will   cycle   the   four memory frequencies through the display. (3)    Store switch. This switch, placarded STO, al- lows up to four preset frequencies to be selected and entered into the control unit’s memory. After presetting the frequency to be stored, push the STO switch. The upper window displays the channel number of available memory (CH 1 through CH 4); the lower window contin- ues to display the frequency to be stored. For approxi- mately  5  seconds,  the  MEM  switch  may  be  used  to advance through the channel numbers without changing the preset display. Push the STO switch a second time to commit the preset frequency to memory in the selected location. After approximately 5 seconds, the control will return to normal operation. (4)    Tuning  knobs.  Two  concentric  tuning  knobs control the preset or active frequency displays. The larg- er knob changes the 1,000’s and 100’s kHz digit. The smaller  knob  changes  the  10’s,  units,  and  tenths  kHz digits. Each detent of the larger knob changes the fre- quency in the display in 100-kHz steps. Each detent of the smaller knob changes the frequency in the display in 1-kHz steps, with the exception that the first two detent positions following a change in rotational direction of the knob will cause a 0.5 kHz change in frequency. Rapid rotation   of   the   smaller   knob   will   cause   frequency changes greater than 1-kHz as a function of rate of rota- tion. Frequencies roll over at the upper and lower limits. The two tuning knobs are independent of each other in that the upper and lower limit rollover of the 10-kHz digit will not cause the 100-kHz digit to change. (5)    Active  switch.  The  active  switch,  placarded ACT, enables the tuning knobs to directly tune the ADF receiver when depressed and held for two seconds. The bottom window will display dashes and the upper window will continue to display the active frequency. Pushing the ACT switch a second time will return the control unit to the normal two-display mode. (6)    Test switch. This switch, placarded TEST, initi- ates the receiver self-test diagnostic routine (Self-test is active only when the TEST switch is pressed). (7)    Light  sensor.  This  built-in  light  sensor  auto- matically controls display brightness. (8)    Volume control. The volume control is concen- tric with the power and mode switch.