TM 1-1510-218-10 3B-9 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 diagnostic (DIAG)  in  the  active  display  and  a  2-digit fault code in the preset display.  Record any  fault codes displayed to   help   the   service   technician   locate   the   problem.   Refer  to  Table  3B-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.    3B-9.  HF COMMUNICATION SET (KHF-950). a.     Description.        The    KHF-950    HF    system consists of three units; the pedestal mounted KCU-951 control panel, the remote KAC-952 power amplifier/antenna coupler, and the KTR -953 receiver/exciter.      The   system   will   operate   on   any 0.1 kHz frequency between 2,000 and 29,999.9 kHz. With    the    capability    to    preset    and    store    99 frequencies for selection during flight, the system also allows   for   selection   of   other   frequencies   manually (direct     tuning)     or     reprogramming     of     any     preset frequency.    The  system  will  automatically  match  the antenna   by   keying   the   microphone.      Power   to   the system  is  routed  through  a  25-ampere circuit breaker, placarded   HF   PWR.      The   receiving   portion   of   the system   is   protected   by   a  5 -ampere   circuit   breaker, placarded   HF   RECVR.      Both   circuit   breakers   are located     on     the     overhead     circuit     breaker     panel, Figure 2-16, Sheet 3. The  HF  system  has  two  methods  of  frequency selection.      The   first   method   is   called   direct   tuning (frequency    agile).        The    second    is    a    channelized operation  in  which  desired  operating  frequencies  are preset, stored and referenced to a channel number. b.    Controls  and  Functions.    Refer  to  Figure 3B-4. (1)   FREQ     Display.          Displays     frequency selected. (2)   Mode   Display.    Displays  selected  LSB, AM, or USB mode. (3)   CHANNEL   Display.      Displays   channel selected. (4)   Light   Sensor.      The    light    sensor    is    a photocell which adjusts brightness of the display. (5)   MODE   Button.      The   mode   switch   is   a momentary push button switch that selects LSB, AM or USB. Table 3B-2.  Self-Test Codes FAULT/ CODE DESCRIPTION FAULT/ CODE DESCRIPTION 00 No fault found 15 Frequency out of range 01 5 Vdc below limit 16   Forward power below limit 02 5 Vdc above limit 17 Transmitter temperature excessive 03 12 Vdc below limit 21 Tuning    voltage    out    of    limit    at    highest    receive frequency 04 12 Vdc above limit 22 Tuning voltage out of limit at 118 MHz 05 Synthesizer not locked 23 Local oscillator output below limit 07 Noise squelch open without signal 24 No-signal AGC voltage too high 08 Noise squelch open without signal 25 Inadequate AGC voltage increase with rf signal 12 BCD frequency code invalid 26 Reflected rf power above limit 13 2/5 frequency code invalid 27 Transmitter timed out 14 Serial message invalid