After making certain that the trouble is not due to a "slip-up" in operation, the part of the equipment causing the trouble should be isolated by systematic tests. The method of making such tests will be outlined later in this chapter.

When the part of the equipment causing the trouble has been isolated, it is usually a fairly simple matter to remedy the fault. The more probable causes of trouble in the various parts of the equipment will be discussed in separate sections.

Should there be any difficulty in locating or correcting the cause of the trouble, the RCA Photophone service engineer should be notified immediately. In the meantime the projectionist should do what he can to get the equipment back into normal operating condition.

The trouble charts included in this chapter should be used as an aid in locating faults. Several charts are used, each one covering a part or type of equipment.

226. Checking For Errors in Operation. -If no sound is obtained when starting, or when "changing-over" from one projector to the other, check for any of the following errors:

(a) Switches or rheostats set incorrectly on the amplifier panels. (While checking the switches and rheostats of the amplifier, inspect the tubes of the voltage and power amplifiers to see that they are all lighted.) See sections 244 and 249 if any or all of the tubes of an amplifier unit fail to light.

(b) "Film-Disc" switch set in the wrong position.

(c) Fader switch set for the wrong projector, or fader potentiometer set in the "off" position or for the wrong projector.

(d) Output fader in the "off" position or wrong one being used. (Output faders are used only on PG-6, PG-7 and PG-8 equipments).

(e) Loudspeakers not plugged in at the stage. (If "no sound" is due to the stage speakers being disconnected, sound can still be heard at the monitor speaker.)

If in checking over the routine operation no error is noted, the trouble would probably be due to some defective part, and the next thing to be done would be to isolate that defective part. To do this, systematic tests should be made.

227. Systematic Tests for Locating a Defective Part. -Usually the most effective method of locating a defective part is by determining to what extent the equipment is still operative. If, when operating from "sound-on-disc", no sound is obtained when starting or changing from one projector to the other, the first thing to be done, after checking to determine if an error has been made in the operating procedure, is to find out if sound can be obtained by using the photo-cell circuit. To do this, change the setting of the "Film-Disc" switch to the "Film" position, light the exciter lamp, and pass a card up and down between the sound gate and photo-cell. If a thumping sound is heard, the indication is that all the equipment except for the pick-up or pickup circuits is functioning properly, so that it is only reasonable to assume that the trouble is either in the pick-up itself or in the "Film-Disc" switch.

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