numbered. Refer to these numbers while you read the following section. 1.   The   GRAY   SCALE   switch   energizes   the circuit  in  the  power  supply-video  converter  WRA, which presents ten shades of gray across the bottom of  the  video  indicator. 2.  The  MODE  switch  is  a  6-position  rotary switch  that  selects  the  mode  of  operation.  In  the STBY  position,  the  system  is  maintained  in  the operational  readiness  state.  The  air  conditioning  and cryogenic  cooling  of  detectors  is  activated.  The receiver head is in the stow position (CCW and up limits). 3.  The  AZIMUTH  knob  controls  the  receiver slew  signals  (azimuth)  in  the  position  mode  of operation. 4.  The  SYS  GO  push  button  illuminates  to indicate  a  good  system  at  the  completion  of  BITE. The  light  can  be  extinguished  by  pressing  the indicator. 5. The BIT ON push button initiates the BITE test sequence. The push button is lit while BITE is in progress.  The  light  goes  out  upon  completion  of BITE. 6.   The   POWER   SUPPLY   FAIL   indicator illuminates if the power supply-video converter fails BITE. 7. The POL switch is a two-position switch that selects   the   polarity   of   video   signals   from   the postamplifiers  of  the  receiver-converter  detector  array video amplifier circuits. In the WHT HOT position, the hot targets appear white on the video indicator. In the BLK HOT position, the hot targets appear black on  the  indicator. 8. The FOV switch selects either wide (WIDE) or   narrow   (NAR)   field   of   view.   It   does   this   by switching  an  afocal  lens  assembly  in  or  out  of  the optical  path  of  the  receiver. 9.  The  GAIN  knob  adjusts  the  dc  level  of  the video output to the video indicator. This affects the contrast of targets on the indicator. 10. The LEVEL knob adjusts the dc level of the video  output  of  the  receiver-converter.  This  affects the  brightness  of  the  background  on  the  video indicator. 11.   The   RCVR   CONV   FAIL   indicator illuminates  if  the  receiver-converter  fails  BITE  test. 12. The FOCUS switch is a four position rotary switch that selects target range for focusing the afocal lenses in the narrow FOV. 13. The RTCL BRT knob controls the brightness of the reticle that is superimposed on the video signal applied  to  the  video  indicator. 14.  The  NOT  READY  indicator  illuminates when   the   receiver-converter   is   not   at   operating temperature, when gyro spin-up is not complete, or when BITE is in the fault isolation mode. 15.  The  COOLING  indicator  illuminates  to indicate  the  IR  detectors  in  the  receiver-converter have not reached operating temperature. 16.   The   RCVR   O   TEMP   indicator   shows excessive  temperature  within  the  receiver-converter. 17.  The  SERVO  FAIL  indicator  illuminates  if  the control  servomechanism  fails  the  BITE  test. 18. The ELEVATION knob controls the receiver slew   signals   (elevation)   in   the   position   mode   of operation. VIDEO INDICATOR The   typical   video   indicator   (fig.   6-18)   is   an 875-line,   30   frames-per-second,   closed-circuit   TV monitor.  On  the  front  of  the  WRA  is  an  ON-OFF power  switch,  an  elapsed  time  meter,  brightness  and contrast  controls,  and  a  status  indicator.  Operation  of the  indicator  is  similar  to  that  of  a  TV  monitor. Figure 6-27 is a simplified block diagram of a video indicator’s  signal  processing  circuits. Composite  video  from  the  video  line  driver module  of  the  power  supply-video  converter  is applied to the video amplifier/sync stripper module. This   module   separates   the   video   signals   (IR, RETICLE, GAI, and gray scale) from the sync signals (blanking,   clamping,   and   sync).   The   module amplifies  the  video  signals  and  provides  the  video output  to  the  CRT  for  display.  The  contrast  control  is also  injected  in  the  video  amplifier/sync  stripper module. The module also sends the composite sync signals  to  the  vertical,  sync,  CRT  protect,  and brightness  control  module. The   video   amplifier/sync   stripper   module processes  the  composite  sync  signal.  It  provides vertical and horizontal sync signals to the vertical and horizontal sweep module. It also provides blanking and  clamping  signals  to  the  CRT.  The  brightness 6-26