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262. AC Projector Drive Motors. -Should the AC motor fail to start check the following:

(a)    AC line switch open.

(b)   Blown fuses in AC line.

(c)   Defective switch. There is a possibility that a burned out switch contact on the projector is preventing current from reaching the motor. Do not turn "off" the motor switch until the motor has reached full speed unless it is absolutely necessary, as this causes an arc in the switch. After some time such an are is likely to ruin the switch contacts completely.

(d)   A burned out resistor in the three-phase motor line. Bring the projector up to running speed by cranking it with the power turned "on" and, if the motor will keep the projector running, it usually is a sign that one of the resistors in the AC line has opened, probably burned out. Of course, if the two resistors have burned out, which should never occur, the motor would not drive the projector under any condition. Should the condition be found where the motor will not run unless it has been cranked up to synchronous speed, it can be temporarily fixed by "shorting out" the defective resistor, but the equipment should not be left in this condition for any length of time, as the machine will come up to speed too quickly and too great a strain on the mechanism will result.

(e)   A burned out resistor in any single-phase AC motor line must be replaced before the equipment can be operated. Notify the RCA Photophone service engineer.

(f)   If excessive vibration occurs, check all bolts to see that the motor is bolted tight to the base, and also make sure that the drive sprockets have not slipped out of alignment. See sections 28 and 29.

See also sections 31 and 32.

263. DC Projector Drive Motor. -If the DC projector motor fails to start look for the following troubles:-

(a)   DC line switch "off".
(b)   Blown fuses.
(c)   Dirty switch contacts.

If the drum type switch is used, make sure that the contacts in the switch are clean and bright. Dirty or pitted contacts can cause much trouble.

If the motor picks up to a speed much in excess of normal, look for dirty contacts in the centrifugal switch.

If excessive sparking is noticed at the commutators of DC motors or generators, coating the brushes very lightly with tallow will greatly help to reduce it. Keep the commutators clean. When brushes become excessively worn, replace them with new ones. With proper care the motor will give very little trouble. Never oil the DC motor. See section 27.

CAUTION.-Never leave the drum control switch in the "Brake" position. The brake may be used to stop the motor when necessary, but must be immediately returned to the "Off" position. Be sure to keep your fingers out of the end casting of the motor at the flywheel end. This is dangerous as there is a fan inside of this opening and injury may result.


Chapter Fourteen Pages
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