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 TM 55-1905-220-14-11
5-117. SHIP'S COURSE INDICATOR-MAINTENANCE INSTRUCTIONS (Continued).
8
Away from null the 36X signal may be large or small, and the 1X signal is always large. When the
36X signal is large, the diodes in parallel with it present a low impedance and bypass the signal
around transformer T1. In the presence of a large 1X signal (in excess of about one volt) the diodes
in series present a low impedance and thus pass the 1X signal to input transformer T1.
9
In addition, the anti-stickoff voltage is added in series with the 1X signal by the 2.5-volt secondary
winding of power transformer T2. Series resistors R8 and R9 prevent the amplifier from excessively
loading the synchros.
(e) Servomotor.
The servomotor is a conventional two-phase type. A capacitor in series with the motor reference winding
produces a phase displacement relative to the control winding. This displacement results in a revolving magnetic field,
when both windings are excited, which causes the armature to rotate. The servo motor is a closed assembly with
lubricated and sealed bearings.
c.
Maintenance Instructions.
(1) Care and cleanliness in the handling of ship's course indicators will do much to minimize their need for
maintenance. Never use excessive force to get parts apart or together. The only test equipment required to work on the
indicator is an electronic or precision a-c voltmeter, used for resistance and voltage measurements, and for zeroing the
When the SCI is disassembled for repair or lubrication, protect gear train
including teeth, shafts, and bearings from scratches and other damage.
Keep the gear train clean, preferably by preventing dust and dirt from
entering the indicator mechanism.
(2) Lubrication.
(a) The instrument gear trains are precision assemblies that operate to position the balanced dials. As a
consequence, the gears need transmit little power. Keep then clean, as dust may collect between the teeth with resulting
binding. Keep synthetic gears clean and free of lubricants.
(b) The metal gears should be cleaned and lightly coated with MIL-G-3278 or MIL-G-23827 grease during
the yearly inspection or when the indicator is disassembled for repair.
5-1314
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