Richardson's handbook of projection (1930)

1312 HANDBOOK OF PROJECTION FOR equipment used exclusively by the one at fault, and may therefore confine our search to it. If we have done the various things before set forth and have found everything thus far to be all right, we then must proceed to find out in just what other part of the system the trouble lies, remembering, however, that it is not impossible, or even improbable that it may be caused by two or more small faults, each one of which we find and remedy probably will make the others the more easy to locate. FIRST, IF THERE BE NO SOUND AT ALL, we must test, using head phones, to see just how far the sound is going through the system, in which we may limit our investigation by trying out a disc record. If we get silence from a film but sound from a record (being sure the film used carries sound of normal volume), then we need only to investigate the photo-electric cell batteries, the film disc transfer switch, the photo-electric cell amplifier and the film attenuater. WARNING. — In testing never use a film carrying low volume sound. It is good practice to secure a strip of film suitable for such tests and keep it ready for use. Don't use a low volume disc or film and then blame the apparatus because the volume is low. Having examined the exciting lamp, its filament, its setting and the condition of its globe, as before directed, and either found or put them all into perfect condition, connect the head phones across the photo-electric cell amplifier output terminals. If everything is as it should be you will be able to hear the sound, though, of course, not at large volume. The photo-electric cell amplifier terminals location will vary with the system used. Those