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The voice coil supply circuit continuity may be checked at each speaker by using a pair of head phones across the incoming voice coil leads. If sound at the voice coil and field current are obtained and the speakers do not operate, call the service man, but usually it will be found that, if no sound issues from a speaker, one of the leads is open. It is quite possible that the trouble may be found in one of the plugs.

229. Defective Pick-Up.- When sound can be obtained from one pick-up and not from the other, the most probable cause of failure to obtain sound is that the pick-up itself is defective. This should be checked by replacing it with a new pickup. When removing a pick-up, loosen the set screw which holds it to the tone arm just enough to free it and pull the pick-up straight out. (Do not remove the set screw entirely, or the fine wires in the pick-up will be broken when the pick-up is removed.)

230. Low Volume When Using Discs.- If the volume obtained from both projectors is low when using discs the indication is that the voltage amplifier is defective. Switch to the other voltage amplifier if one is available. Check the voltages of the voltage amplifier.

If the volume from one pick-up is low while the other is OK the indication is that the pick-up is defective. Replace the pick-up.

231. Unequal Volume from Pick-Ups. -If a greater volume is obtained from one pick-up than from the other, the volume level should be equalized. The volume of the sound from the two pick-ups can be equalized by means of a potentiometer mounted in the "Film-Disc" box except in the case of the PG-10 and PG-13 equipments where the potentiometer is located in the terminal box on the side of the turntable. Two different types of potentiometers are used. One consists of resistance wire wound on a tube with a movable contact which can be slid along the wire. The other is built like an ordinary radio potentiometer, with a resistance wire wound on a circular form and a movable arm for adjusting the point of contact. This arm is fastened to the shaft of the device and the shaft is slotted for the insertion of a screw driver blade.

To adjust for equal volume on two pick-ups use two records of the same selection and start both at the same time. Then fade from one projector to the other and adjust one of the potentiometers until the volume obtained from both pick-ups is the same.

232. Pick-Up Needle jumps the Groove. -If the pick-up needle jumps the groove the trouble may be due to:-warped discs, turntable not level, tone-arm binding, or the bottom of the pick-up striking the records due to the use of short needles.

233. Poor Quality When Using Discs. -Poor quality when using discs may be due to poor discs, dirty discs, or a defective pick-up. The pick-up can be checked by testing with a record known to be good. If the quality of the sound from one projector is normal while the sound from the other is not, the trouble is probably due to a a defective pick-up.

234. "Wows" When Using Discs. -"Wows" when using discs may be due to the lubricant of the viscous damping device being too heavy. In cold booths where the Alemite grease might become hard, it is advisable to run the projectors for fifteen minutes before the show to warm the lubricant to the normal temperature. If the "wows" continue after the lubricant has been warmed by running, check the viscous damping device as described in section 71.


Chapter Fourteen Pages
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