Change 3 3-57
Figure 3-24. VHF Navigation Receiver Control Unit
(5) Active switch. The active switch, placarded
ACT, enables the tuning knobs to directly tune the receiv-
er when depressed and held for two seconds. The bot-
tom 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 2-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.
(9) Power and mode switch. The power and mode
switch contains three detented positions placarded OFF,
ON, and HLD. The ON and OFF position switches sys-
tem power. The hold (HLD) position allows the navigation
receiver frequency to be changed while holding the DME
in its present frequency.
(10) Annunciators. The receiver control unit con-
tains MEM (memory) and RMT (remote) annunciators.
The MEM annunciator illuminates whenever a preset
frequency is being displayed in the lower window. The
RMT annunciator is not used in this installation.
(11) Preset frequency display. The preset (inac-
tive) frequency and diagnostic messages are displayed
in the lower window.
(12) Compare annunciator. An annunciator plac-
arded ACT normally illuminates when frequencies are
being changed. The ACT annunciator flashes if the actu-
al radio frequency which the receiver is tuned to is not
identical to the frequency shown in the active frequency