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 TM 55-1905-223-24-3
(a) Check the tightness of the semiconductors to ensure good mechanical and electrical connection.
Tighten the semiconductors to 36-42 in-lb (4.06-4.74 N ) torque.
m
(b) Disconnect the flexible lead to each semiconductor (1, Figure 3-6) and check the forward and
reverse resistance. Use a multimeter on the 10,000 ohms scale and check the semiconductor
resistance.
1
A good semiconductor will give a high resistance (infinity) in the reverse direction, and a low
resistance in the forward direction.
2 An open semiconductor will give a high resistance reading in both directions, and a low
resistance reading in both directions for a shorted one.
(c) Check the varistor (6, Figure 3-6) surge suppressor using a multimeter. The varistor is
connected across the two rectifier plates to prevent reverse voltages from damaging the
semiconductors.
1
A good varistor will show a high resistance (virtually infinity) reading in both directions.
NOTE
A defective varistor will be burnt, missing, or have the lead wire
burnt off.
2
A defective varistor will show a full-deflection (short-circuit) reading in both directions.
(d) Replace defective semiconductors and varistor as necessary (see Disassembly and Assembly
steps of this procedure).
(5) With the generator shut down, and electrical power OFF to the machine, check the main excitation
windings.
(a) Check the exciter stator resistance. Remove leads Xand XX from the manual voltage regulator.
Using a multimeter measure the resistance between leads X and XX. Refer to Table 3-2 for the
correct winding resistance (reading).
Table 3-2. Winding Resistance (Ohms)
Main Stator (per phase)
Main
Stator
Rotor
Rotor
21.0
0 (0.17)
0 (0.009 to 0.011)
1.20
3-21
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