Do not remove any parts without first opening the main line switch, to the
projector. Setting the drum to the "Off" position is not enough.
A fly-wheel is mounted on the motor shaft. The purpose of the fly-wheel is to
keep the motor running smoothly by preventing sudden changes of speed.
Inside of the motor casting is a heavy fan which rotates with the armature
shaft. The purpose of this fan is to cool the motor windings.
Be sure to keep
fingers out of the end of the motor castings while the machine is in operation.
The motor runs on ball bearings which are packed in grease and require no
attention other than a yearly renewal of this grease. This will be taken care of
by the service man.
Do not attempt at any time to oil the DC motor.
If the motor fails to start look for blown fuses in the DC supply line.
If the motor runs at excessive speed, inspect the centrifugal switch for dirty
or burned contacts. If this switch does not close, the motor will run at too high a
If trouble is experienced at any time with the switch contacts of either the
drum-switch or the three-position speed-selector switch, the covers may be removed
(after opening the main line switch) and the contacts inspected for burned points.
It is advisable to coat the contacts of the drum-switch with vaseline, which will
allow the switch to turn more easily and reduce the wear on the contacts. The
bearing of the drum-switch has an oil hole as shown in Figure 16. It should be
oiled about once a month with a good grade of machine oil.
28. Synchronous Motors.- A 220 volt, 60 cycle, 3 phase, synchronous motor is
used as standard equipment on PG-1, 2, 3, 4, 6, 7, and 8 equipments when the proper
power is available.
The speed of a synchronous motor depends upon the frequency of the power
supply. It is called a synchronous motor because it runs at a speed corresponding
to the speed of the generator. These motors can be built to run at different speeds
by building the motor with different numbers of poles. A synchronous motor which
has two poles will run at 3600 r.p.m. (revolutions per minute) on a power supply
whose frequency is sixty cycles per second. A four pole motor would run at 1800
r.p.m. and a six pole motor at 1200 r.p.m. The synchronous motors used in RCA
Photophone equipment have four poles and run at 1800 r.p.m. on a 60 cycle circuit.
The action of this motor is as follows:-When a three-phase alternating voltage is applied to the winding of a three-phase motor, a magnetic field is created
which rotates at a constant speed (if the frequency of the power supply is constant).
The speed of the rotation of the magnetic field is such that it passes over two poles
for every complete cycle of alternating voltage. Therefore, in a four pole motor, two cycles
are required for each complete revolution of the magnetic field around the motor.