One of the duties aboard ship will be to keep the synchro systems used in ordnance equipment in good working order. Therefore, Gms must be familiar with the do's and don'ts of synchro maintenance and repair.

The following is a list of don'ts: . Do not attempt to zero a synchro system that is already accurately zeroed because of a desire for practice. Quite often this unnecessary practice results in misalignments. l Do not attempt to take a synchro apart, even if it is defective. A synchro is a piece of precision equipment that requires special equipment and techniques for disassembly. If the synchro is faulty, return it to the supply department if they require it for turn-in and draw a replacement. l Never attempt to lubricate a synchro. A synchro, unlike an electric motor, does not require periodic lubrication. l Never force a synchro into place, drill holes into its frame, use pliers on the threaded shaft, or use force to mount a gear or dial on the shaft.

Signal lights indicate either overload conditions or blown fuses. An overload indicator is actuated by excess current flowing in the stator windings. In one form of indicator, a neon lamp is connected to the stator leads by means of two transformers. The primary, consisting of a few turns of heavy wire, is in series with two of the stator leads; and the secondary, consisting of many turns of fine wire, is in series with the lamp. The turn ratio is such that when excess current flows through the stator windings, the neon lamplights. For example, when the difference in rotor positions exceeds approximately 18 degrees, the lamp lights, indicating that the load on the receive shaft is excessive.

Fuse indicators are panel lights that glow when a fuse in the rotor circuit blows. If excessive current flows in the rotor windings due to a short circuit or excessive mechanical overload, one of the fuses will glow and the neon lamp across that fuse will light. Another type of blown fuse indicator uses a small transformer with two identical primaries and a secondary. With both fuses closed, equal currents flow through the primaries that induce mutually canceling voltage in the secondary. If a fuse blows, the induced voltage from one primary is present in the secondary and the lamp lights.

Synchro maintenance and troubleshooting is a very complex undertaking in modern ordnance equipment, and skilled personnel with ordnance rates work jointly to maintain the synchro systems in a high degree of readiness. The Navy Handbook, MIL-HDBK-225 (AS), is devoted to synchro troubles and should be used during analysis of synchro system casualties. The tables contained in this publication are useful tools for learning the many problems that may exist in synchro systems.

If the casualty exists in the transmitter, all receivers will be affected. If the casualty exists in a receiver, only that receiver will be affected, except in the case of shorted stator leads, when all synchros will be affected.

A list of synchro casualties and effects on a typical synchro system follows:

^1. S1 and S3 shorted-rotor locks on 0 degrees or 180 degrees.

2. S1 and S2 shorted-rotor locks on 120 degrees or 300 degrees.

3. S2 and S3 shorted-rotor locks on 240 degrees or 060 degrees.

^4. S1, S2, and S3 shorted-rotor spins.

5. R1 or R2 shorted-rotor aligns as 090 degrees or 270 degrees from the signal; fuse blows.

6. R1 or R2 open-rotor aligns at 0 degrees or 180 degrees; proper rotation, poor torque.

7. S1 open-rotor oscillates over S1 or 180 degrees from S1.

8. S2 open-rotor oscillates over S2 or 180 degrees from S2.

^9. S3 open-rotor oscillates over S3 or 180 degrees from S3.

10. R1 and R2 reversed-rotor aligns 180 degrees from signal; proper rotation, good torque.

^11. S1 and S2 reversed-rotor aligns at 120 degrees from signal; reversed rotation, good torque.

^12. S2 and S3 reversed-rotor aligns at 240 degrees from signal; reversed rotation, good torque.

13. S1 and S3 reversed-rotor aligns at 0 degrees; reversed rotation, good torque.

Synchro units require careful handling at all times. For more information on synchros, refer to the Navy Electricity and Electronics Training Series (NEETS), Module 15, Principles of Synchros, Servos, and Gyros, NAVEDTRA 172-15-00-80.