replace lamps. These tasks are extremely impor- tant  for  continued  operating  efficiency. There is a tendency for film emulsion to rub off the film and build up at certain places in the film  path.  Caked  emulsion  or  burrs  can  cause loop   loss   due   to   nonclosing   of   sprocket   shoe locks.  Other  problem  areas  are  excessive  film slap  which  is  due  to  a  dirty  gate;  jammed  film splices   in   sprocket   shoes;   clicking   noises   and fading  high  frequencies  which  are  due  to  dirty sound   drums;   and   the   sticking,   ejection,   or pileup of film in the takeup sprocket shoe areas. Cakes  or  burrs  on  film  guides,  shoes,  aperture, or  pressure  plates  often  cause  film  scratches. These are a few of the troubles that could result. Any obstruction in the film path can be expected to  interfere  with  proper  transportation  of  the film.  You  will  save  time  by  cleaning  the  film path and, at the same time, make an inspection of lenses and lamps after each reel is shown. FILM  PATHS.—All  film  path  areas  must  be kept   free   from   emulsion   buildup   or   other foreign  materials.  Never  use  metal  tools  to remove  material  adhering  to  guides,  rollers,  or sprocket  shoes.  Metal  tools  could  do  damage  to some of the parts. Use an orange stick, a plastic rod, or   a   toothpick   whenever   scraping   is necessary.  Soft,  lint-free  cloth,  lens  tissue,  or  a pipe  cleaner,  dampened  with  acetone,  naphtha, or  isopropyl  alcohol  are  very  convenient  for removing  emulsion  from  the  film  path  and  for cleaning in restricted areas. Tricholorethylene or carbon   tetrachloride   should   NOT   be   used   as cleaning  solvents  because  they  might  stain  or damage  plastic  parts.  They  are  also  toxic.  Wipe all threading guides (if the projector is designed for  automatic  threading)  with  a  soft,  lint-free cloth  or  a  brush  moistened  with  any  naphtha- base solvent. Film jump could result from a dirty film  gate;  therefore,  the  gate  should  be  wiped clean. A dirty aperture may cause poor focus; so clean  the  aperture  plate  and  the  pressure  plate with  an  aperture  brush  or  with  a  soft,  damp, lint-free  cloth.  Clean  the  aperture  side  tension rails and the aperture opening. Be sure that all caked  emulsion  and  lint  are  removed.  Do  not remove   the   aperture   plate   for   daily   cleaning because  a  special  tool  is  required  to  realign  the plate.  Clean  and  inspect  all  film  spocket  shoes and  rollers.  Use  a  soft,  damp  cloth  to  clean  the surface  of  the  sound  drum  that  contacts  the film. CLEANING     THE     LENSES.—Clean     the lenses if the projector is used daily. The lenses of the  16-mm  projector  can  be  removed  for  clean- ing   without   too   much   difficulty.   Follow   the instructions  for  removal  and  replacement  of  the lenses published in the appropriate instructional manual  or  technical  order. Clean  the  external  glass  surfaces  of  the projection  lens  and  examine  them  for  cracks, scratches,   or   chipping.   The   projection   lens   of some  models  may  be  removed  by  loosening  a lens lockscrew and removing the lens. On others, the projection lens may be removed by threading the lens out as far as it will go, turning the focus knob  in  a  counterclockwise  direction,  and  then lifting  the  lens  out.  Clean  the  exposed  surfaces of the lens elements by wiping them gently with lens tissue. If wiping the lenses with lens tissue does not clean them, apply a drop of lens cleaner to  the  lens  tissue.  Then  wipe  the  lens  surfaces gently  with  the  damp  lens  tissue.  Do  not  apply lens cleaner directly to lens elements because it may  eventually  cause  the  lens  coating  to  come off. Insert the cleaned lens into the carriage and reposition  it  by  turning  the  focusing  knob clockwise to engage the lens or by inserting the lens  into  the  lens  mount  and  locking  the  lens lockscrew. To  clean  the  reflector  and  the  condensing lenses,  you  must  be  familiar  with  the  projector. Some  of  the  newer  models  have  the  reflector built into the lamp. Some are so constructed that the  condensing  lenses  should  not  be  removed from  their  carriage.  With  some  models,  you  can get to the reflector and condensing lens assembly by  opening  the  lamp  house  and  lifting  out  the projection  lamp.  The  condensing  lens  assembly can  be  lifted  out.  With  the  condensing  lenses removed,  you  can  clean  the  reflector  with  lens cleaning tissue. If grease has accumulated on the reflector, remove it by first wiping it with a soft, lint-free cloth dampened with lens cleaner; then wipe it with cleaning tissue. Clean the two out- side surfaces of the condenser lenses in the same way  and  then  reassemble  the  reflector  and lenses. With some models, when the lamp house cover is removed, the carriage for the condenser lenses  can  be  rotated  down  and  out  of  the 7-30