Beechcraft C-12C Operator And Technical Reference Manual page 254

TM 1-1510-218-10
(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.
The ACT annunciator's 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.
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.
desired channel number has been selected, push the
STO button again to store the frequency.
When storing a frequency, the second
actuation of the STO button must be done
within 5 seconds after selecting the
channel number or the first actuation of the
STO button. 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
button. Memory is retained even when the unit is
turned off for an extended period of time.
(5) Stuck Microphone Switch. Each time the
push-to-talk switch is pressed, the microprocessor in
the transceiver starts a 2-minute timer.
3A-12
NOTE
To program the
After the
NOTE
The TX
annunciator on the transceiver control unit will be
illuminated whenever the transmitter is transmitting. If
the transmitter is still transmitting at the end of
2 minutes, the microprocessor turns it off.
intentional transmissions last much less than 1 minute;
a 2-minute transmission is most likely the result of a
stuck microphone switch. This timing feature protects
the ACT channel from long-term interference.
When it turns
microprocessor switches the transceiver to receive
operation. A stuck microphone switch will prevent you
from hearing received signals, or the two warning
beeps. The microprocessor then waits until the push-
to-talk switch opens to sound the two beeps.
To transmit for more than 2 minutes, release the
microphone switch briefly and then press it again. The
2-minute timer resets and starts a new count each
time the microphone switch is pressed.
(6) Overtemperature
microprocessor regularly monitors the temperature of
the transmitter. If the transmitter gets too hot during a
transmission, the microprocessor
transmission, and the sidetone will cease. When the
microphone switch is released, you will hear two
beeps. Press the TEST switch on the transceiver
control unit to observe the fault code. As long as the
temperature remains above the limit, the micro-
processor will not respond to a normal push of the
microphone switch. If you must transmit, however,
you can override the protection by rapidly keying the
microphone switch twice, holding it on the second
push. The shutdown temperature is 160 °C (320 °F).
(7) Self-test.
diagnostic routine can be initiated in the transceiver by
pushing the TEST button on the transceiver control
unit. The control unit will modulate the active and
preset display intensity from minimum to maximum to
annunciate that self-test is in progress. Several audio
tones will be heard from the audio system while the
self-test routine is being executed. At the completion
of the self-test program, the transceiver control unit will
usually display dashes in the active display, and 00 in
the preset display. This indicates normal operation. If
any out-of-limit condition is found, transceiver control
unit will display DIAG in the active display and a 2-digit
fault code in the preset display.
codes displayed to help the service technician locate
the problem. Refer to Table 3A-2 for a description of
the self-test fault codes that can be displayed on the
transceiver control unit. The TEST button must be
pushed before any fault code can be displayed.
off the transmitter,
Protection.
will stop
An extensive self-test
Record any fault
Most
the
The
the