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MAINTENANCE AND INSPECTION 191
/. Loudspeakers
Failure to operate, rattling, and similar objectionable noises may be localized to a group of two loudspeakers byuse of the sectionalizing panel as described under "Weekly Inspection and Check," page 185.
If the sound fails in one or all of the auditorium loudspeakers when the signal is evident in the monitor loudspeaker, check:
j. Loudspeaker field supply
Remove cover from the sectionalizing panel and test the voltage across terminals Fi and F2 on the sectionalizing panel with a 250-volt test lamp. In case no voltage is evident, check the fuses marked " Loudspeaker Field." If these fuses are all right, check the meter reading from the jack ECX50. If no voltage can be measured here, the trouble is probably in the motor-generator set. (See "Motor-Generator — Adjustments," page 190.) When the voltage at the above points is good test the voltage at each group of loudspeakers. If there is no evidence of trouble here check the signal circuit.
2. Signal circuit
If all the loudspeakers are "dead" and everything else is all right, then the signal cable from the terminal "LSC" on the sectionalizing panel is open, or a cone is short-circuited. If a cone is short-circuited the trouble can be cleared by checking each group of loudspeakers as described under "Weekly Inspection and Check — Loudspeakers," page 185. The short occurs in the group of loudspeakers from which no sound can be obtained. When a short circuit occurs in a certain group this group should be left out until the trouble can be corrected by an R. C. A.Photophone service representative.
Rattling noises of distortion of the sound may be caused by the fact that the loudspeaker cone is not