housing. Clean the outside surfaces of the lenses as described above and then replace the carriage. P R O J E C T I O N    L A M P    R E P L A C E - MENT.—To   replace   the   projection   lamp,   turn off the projector and disconnect the power cord. Allow  the  upper  portion  of  the  lamp  house  to cool  before  handling  it.  Remove  the  lamp  house cover.  If  the  projector  has  a  lamp  ejector  lever, lift the lever gently to release the lamp from the socket. Remove the lamp by hand. If the lamp is hot,  use  a  glove  or  cloth.  The  base  of  a  projec- tion   lamp   is   designed   with   either   flanges   or prongs  to  hold  it  in  position.  To  remove  lamps equipped   with   flanges,   press   the   lamp   down firmly,  turn  it  counterclockwise  90°,  and  lift  it out.  For  the  lamps  equipped  with  prongs,  pull the lamp straight out. Replace the burned-out lamp with a lamp of the same wattage and type. Remember to have a spare bulb available. To   install   a   new   projection   lamp   with flanges, line up the wide and narrow flanges on the  base  of  the  lamp  with  the  corresponding lamp  socket  slots  and  insert  the  lamp  with  the socket. Press the lamp down firmly and turn in a clockwise  direction  until  it  locks  in  place.  To install  a  projection  lamp  with  prongs,  set  the new  lamp  into  the  socket  and  rotate  it  slowly until  the  prongs  settle  into  the  proper  recep- tacles.  The  lamp  will  fit  only  one  way. Try  not  to  get  fingerprints  on  the  projection lamp,  but  if  there  are  any  prints  on  the  lamp, wipe  them  off.  Fingerprints  on  the  lamp  reduce the light output and cause the bulb to get too hot in  the  area  of  the  fingerprint.  This  causes  this area to expand and may possibly cause the lamp to shatter. After  installing  a  new  lamp,  always  project the light on the screen and focus the image of the aperture.   If   the   light   distribution   is   uneven, adjust the position of the lamp as directed by the operation  manual  or  technical  order  for  the specific   projector. When  the  appropriate  projection  lamp  has been installed, reassemble the lamp house cover. EXCITER   LAMP.—Generally,   the   exciter lamp  cover  and  the  exciter  lamp  can  be  easily removed  and  replaced  without  the  use  of  tools. The   exciter   lamp   cover   acts   as   a   dampening shield which covers the exciter completely except on  the  side  facing  the  sound  lens.  This  cover eliminates   stray   reflection   within   the   exciter lamp chamber and prevents any light, other than the   direct   beam   from   the   exciter   lamp,   from entering the sound optical system. To remove and replace the exciter lamp, first turn the volume control switch to the OFF posi- tion.  Disconnect  the  power  to  the  projector. Then remove the exciter lamp cover by loosening the  thumbscrew  until  the  cover  can  be  lifted from  the  projector.  Note  the  location  of  the registration  pins  that  align  the  cover,  as  these must   be   repositioned   precisely   to   replace   the cover. Move the exciter lamp release and locking lever  to  its  extreme  right-hand  position.  This releases  the  registration  pins  and  permits  the lamp  to  be  lifted  from  the  socket.  Clean  the exciter  lamp  with  a  clean  cloth  or  lens  tissue. Avoid  leaving  fingerprints. The sound lens is partially exposed when the exciter  lamp  cover  is  off.  Clean  the  sound  lens, with  one  face  exposed  toward  the  exciter  lamp and  the  other  face  exposed  toward  the  sound drum, by blowing air across the external surfaces of  the  lamp  with  a  syringe  bulb.  Remove  any remaining dust or dirt with a camel’s-hair brush; then  use  a  lens  tissue  to  wipe  the  lens  surface clean.  Do  not  attempt  to  move  the  sound  lens from  the  projector  or  disturb  the  setting  of  the lens. Clean the external surfaces of the lens. When installing a new exciter lamp, place the lamp   base   openings   over   the   appropriate registration  pins  and  turn  the  exciter  lamp release and locking ring to the extreme left-hand position. This will seat the lamp firmly in place. Wipe the exciter lamp with a clean cloth or with lens  cleaning  tissue  to  remove  fingerprints.  The exciter lamp is prefocused and no adjustment of this lamp or its socket is required. The  exciter  lamp  cover  may  now  be  rein- stalled. If the exciter lamp cover is designed with registration  pins,  you  must  match  the  pins  to specific  holes.  Seat  the  cover  firmly  and  hold  it in position while tightening the thumbscrew. DRIVE BELTS.—Most projectors are designed  to  use  two  drive  belts.  A  takeup  belt drives   the   takeup   reel   during   projection,   a rewind belt rotates the film reel on the feed reel 7-31