If no sound is obtained from either the pick-up or photo-cell circuit, the other projector should be "faded in" and tested. The pick-up and its circuit can be tested by stroking the needle point with a finger and listening for a plucking sound in the loudspeaker. The photo-cell and its circuit can be tested by the method outlined above. If sound can be obtained from one projector and not from the other, the indication is that the defect is in the fader relay or fader potentiometer (depending on which device is used on the equipment) or in the "Film-Disc" switch. The reason for this conclusion is, that it is not probable that both the pick-up and photo-cell would fail at the same time.

A similar procedure should be followed if trouble develops when operating from sound-on-film.

If it is found that sound cannot be obtained from either projector, the indication is that the trouble is in the voltage amplifier or power amplifier. The voltage amplifier can be checked by changing over to the other voltage amplifier if one is available. If a second voltage amplifier is not available, but a nonsynchronous turntable attachment is, the amplifiers can be checked by plugging the nonsynchronous turntable input plug into the jack provided, and listening for sound while scratching the needle of the turntable pick-up. If sound can be obtained from the non-synchronous turntable and not from the projectors, the indication is that the amplifiers are O.K. and the defect is in the fader relay or potentiometer.

If no sound can be obtained from either of the projectors or from the non-synchronous turntable, the indication is that the trouble is in one of the amplifier units. If a second voltage amplifier is available and it is possible to get sound from one but not the other, the fault will be found to be in the voltage amplifier unit from which no sound can be obtained. Of course, in this case it will not be necessary to repair the defective unit immediately, but it should be checked over at the first opportunity.

If only one voltage amplifier unit and one power amplifier unit is used with the equipment, no simple tests can be made to isolate the defect to one of them. In this case it will be necessary to check over both units for defects. If two power amplifier units are used, it is reasonable to assume that both of them will not develop a defect at the same time. Therefore, if no sound can be obtained from either power amplifier units the indication is that the defect is in the voltage amplifier unit; and, if sound can be obtained from one power amplifier unit and not from the other, the indication is that the power amplifier from which no sound can be obtained is defective.

228. No Sound From the Stage Speakers - Sound OK at the Monitor Speaker. - In case no sound is obtained at the stage and the sound is - OK at the monitor speaker, the trouble must be somewhere in the line leading from the amplifier rack to the stage speakers. Where stage plugs are used, it is possible that these plugs have not been inserted, or when being inserted one of the contacts may have become broken. Check speakers for field continuity by removing each of the field plugs at the speakers one at a time and by inserting the leads of a 100 volt test lamp which should not be over 25 watts capacity. (See section 252.) If light is obtained at this point the field continuity is O.K.

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