235. No Sound When Using Sound Film. -No sound when using sound film may be due to a burned out
exciter lamp, sound gate light aperture completely clogged, or a defective photo-cell. To determine
whether the aperture is clogged or not, place a card between the sound gate and the photo-cell
housing. A round circle of light should be obtained at this point. If light is obtained on the card and no
sound is obtained, the indication is that the photo-cell is defective and should be replaced.
236. Low Volume When Using Sound Film. -Low volume when using sound-on-film may be due to any
of the following:-incorrect exciter lamp current, dirty or old exciter lamp, exciter lamp out of focus, sound
gate aperture partly clogged, or a defective photo-cell.
237. Unequal Volume From Projectors When Using Sound Film. -If unequal volume is obtained from the
two projectors when using sound film, the projector giving the lowest volume should be checked for
trouble. See section 236. If no cause is found for low volume the output of the projectors should be
balanced by adjusting the exciter lamp currents. To do this, adjust the exciter lamp current of the
projector giving the lowest volume to its usual value and adjust the exciter lamp current of the other
projector to give an equal volume; then, if necessary, increase the setting of the volume control.
238. Poor Quality From Sound Film. -Poor quality of sound from sound film may be due to any of the
following causes:-poor sound film, dirty sound gate, dirty film, dirty constant speed sprocket, or a
Poor quality of sound is often blamed on the equipment when the fault is in the film itself. On the other
hand, dirt on the film or on the sound gate will ruin the quality of sound from a good recording.
A defective photo-cell can spoil the quality of the reproduced sound.
A photo-cell can be spoiled by misuse. It is important that the photo-cell should not be exposed to
strong light at any time, whether the polarizing voltage is applied or not. They should be handled
gently and not jarred. When no film is in the projector, the circle of light from the exciter lamp can be
seen on the photo-cell. This circle should be located at the exact center of the plate in case of the UX868 Photo-cell or in the center of the window in case of the UX-867 Photocell. Dirty prongs on the photocell may also cause trouble. These can be cleaned readily with fine sandpaper.
After carefully checking all other possible causes of poor sound it may be assumed that the optical
system is out of focus; in which case the RCA Photophone service engineer should be notified.
239. "Wows" When Using Sound Film. -If "wows" are noticeable when running sound-on-film, it may
be due to dirty sprockets or due to the constant speed sprocket being excessively worn (teeth
undercut). Improper adjustment of the viscous damping device will also cause "wows" and should be
checked carefully. See section 92.