240. Exciter Lamps.- It is very important that the adjustment of the exciter lamps be checked by the projectionist before beginning the show at least once a day, as a loss of volume will be the result of any defect in their adjustment. The proper check and adjustment of exciter lamps in the RCA sound head attachment is outlined in section 89.

Exciter lamps should not be used after they have become excessively dark, but should be replaced. The darkening of the interior surface of the glass not only is detrimental in itself in that it greatly reduces the amount of light available, and thereby decreases the volume of sound, but also is an indication that the lamp is nearing the limit of its "life," i.e., it is about to burn out.

All finger marks should be wiped off the lamp immediately. If the lamp becomes hot while greasy finger marks are upon it, they will be hard to remove later. The condensing lens on the optical system should also be kept clean at all times. The turret in which the exciter lamps are mounted should not be allowed to become loose. If the exciter lamp turret is loose it will be difficult, if not impossible, to keep the exciter lamp focused during the operation of the machine. The large nut at the top of the turret should be tightened if the turret becomes loosened.

241. Aperture Mask Not Completely Effective. -If trouble is experienced with white light on the screen when running Movietone prints, this can very easily be corrected by adjusting the guide rollers in the "Simplex" head just above the aperture. If this roller is adjusted correctly, there will be no white light on the screen at any time.

242. Noisy Fading When Using Sound Film or Discs. -If clicks are heard when moving the fading potentiometer, it may be due to dirt on the contact points. The contacts may be reached for cleaning by removing the knob and taking the four screws out of the escutcheon plate. Immediately behind this plate are the contacts. They may be cleaned with a very fine grade of "crocus" cloth or sandpaper, and then wiped off with a soft cloth. A soft cloth moistened with Carbona is very good for cleaning these contacts or those of any kind of relay.

243. Cross-Talk on PG-10 Equipments. -Should cross-talk develop, that is, if sound is heard from both projectors at the same time, it will usually be found that dirt has collected on the contacts of the relay fader. These contacts may be cleaned very easily by sliding a small card or heavy paper between the contacts. The purpose of this relay is to "short" the output of the projector that is not being operated and, therefore, if dirt collects on the relay points the relay cannot serve its purpose, and sound may be heard from both projectors.

244. Voltage Amplifier Tubes Fail to Light. -If some of the voltage amplifier tubes fail to light while others in the same unit do light, the indication is that the unlighted tubes are burned out, and should be replaced; but if none of the tubes of of a voltage amplifier unit light when the amplifier is turned "on," the indication is that the fault lies somewhere in the "A" supply line (storage battery leads in case of SPU equipments).

If two voltage amplifiers are included in the equipment and the tubes of one amplifier will light when turned "on," but the tubes of the other unit will not light when it is turned "on," the indication is that the trouble is in the change-over switch or switches. These should be switched back and forth several times as the trouble may be due to dirty contacts which may be cleaned by operating the switches.

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