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S T A R T I N G   A N D   T E S T I N G

Page 14

Cleaning Mechanism and Film

Strict cleanliness as regards both the film and the film pick-up mechanism (Fig. 10) is most important.

Dirt on the exciting lamp or on the lenses, or dirt clogging the openings in the aperture plate and tension pad, will lead to low volume and poor quality.

Dirt or emulsion accumulating on the film tracks of the aperture plate and tension pad may lead to scratching of the film.

Dirt on the sprocket in the film compartment may cause unsteady pitch in reproduction.

Dirt, dust, oil, fingermarks, scratches or sprocket-hole cracks on the film will cause noisy operation.

The film must therefore be kept in first-class condition, and the different parts mentioned must be cleaned AT LEAST ONCE EVERY DAY.

A pipe cleaner and tooth-brush should be used for cleaning the sprocket and tension pad. Dust and surplus oil should be wiped off with a dry cloth. Do not scrape the film tracks with a knife or abrasive in cleaning them. The film tracks must always be perfectly smooth and polished to the touch. Run the finger tip over them at least once daily to see that no rough spots are developing due to dirt or emulsion hardening on.

Film should be cleaned by drawing it gently through clean, soft, cloths. Do not use chemicals or "dope" on it.

Sprocket-hole cracks in the film can be avoided by not having excessive tension on it. Use no more tension than is necessary to get a clear picture at the highest projection speed used in the house.

Adjusting Film Exciting Lamp

It is vitally important to have the exciting lamp of the film pick-up apparatus properly adjusted.

To light this lamp, set the film-disc switch (Fig. 1) on the front of the machine at "FILM". Then turn the control knob on the door of the exciting lamp compartment until the meter adjacent reads exactly 3-6 amperes. This value is important.
The object of this lamp is to produce a bright, clear illumination on the sound track of the film and on the photoelectric cell. The light from the lamp passes through the lens tube (Fig. 10). In the side of this tube will be seen a small round window. Take out the removable partition between the lamp compartment and the film compartment, and swing the glare shield in place over the lamp, to avoid dazzling the eyes. Light the lamp; then on looking through the window in the lens tube, a narrow horizontal slit will be seen inside the tube, at the right. The light falling on this slit should be bright and sharply focused, with the slit in the center. On removing the tension pad and holding a small white card or piece of paper in front of the aperture, an oval spot of light will be seen on the white surface. The edges of this spot will be soft and blurred, but otherwise it should be clear and uniform. There should not be shadows at the top or bottom or at the ends.

Check the two points just mentioned AT LEAST ONCE EVERY DAY. Whenever the illumination does not meet these requirements, adjust the lamp as will now be described.

The exciting lamp is mounted on a bracket (Fig. 10). This bracket in turn is mounted on two supporting pieces, which