Chapter 6. REPAIR OF ELECTRICAL UNITS

CHAPTER 6

REPAIR OF ELECTRICAL UNITS

leave a gummy deposit. Place piece

6-1. Alternator Description

The alternator is a 12 volt 3 phase alternating current

of tape over slip ring end frame

generator with built-in rectifiers (diodes) to convert the

bearing (14) to prevent entry of dirt

output to direct current required by the truck electrical

or foreign matter. Also tape shaft of

system.

rotor (7) to slip ring end.

6-2. Alternator Disassembly and Repair

e. Clean brushes (16) with soft, dry cloth if they are to

a. Remove alternator from truck TM 10-3930-627-12.

be reused.

Clean alternator with cloth dampened with cleaning

solvent. Dry thoroughly. Do not allow solvent to enter

Caution: Do not tighten vise more

alternator.

than necessary as this could cause

b. Inspect alternator for cracked housing, bent shaft,

distortion of rotor. Place rotor (7) in

or damaged drive pulley. Turn shaft by hand; it should

a vise and tighten only enough to

rotate freely with no catching or binding. Replace or

permit removal of nut (32) and lock

repair damaged alternator.

washer 131).

Remove nut, lock

c. Test alternator if necessary to determine repairs

washer, pulley, key (38), fan outside

needed, TM 10-3930-627-12.

collar (29), and rotor.

d. To disassemble, remove four screws (2, fig. 6-1),

securing frame assembly (1) to frame (10). Match mark

f. Check rotor for grounds by connecting a 110 volt

frames and use a screwdriver at stator slot to pry apart

test lamp or ohmmeter from either slip ring to rotor shaft

two frames.

or to rotor poles. If lamp lights or ohmmeter reading is

less than 5 ohms, field winding is grounded. Replace

Caution:

Use pressure sensitive

rotor if field winding is grounded.

tape, NOT friction tape, which could

6-1