(1) Inspect brush contact surface of armature. A highly
burnished, dark-copper color indicates satisfactory condition. If
contact surface is rough, pitted, scored, burned in areas, or coated
with hardened varnish or carbon accumulations, resurface commutator
A short circuited or open-circuited armature coil
leaves adjacent commutator bars burned or extremely dark in color.
Check for shorts or openings with test lamp (fig. 5-8) and with
If test indicates short-circuit, carefully inspect
between commutator bars for copper particles or a carbon bridge. If
test and inspection indicate faulty armature coil, replace armature.
(2) If a series of defective commutator bars show burns, trouble
may be due to eccentricity or grease deposits on surfaces.
areas are caused by grease deposits, clean and resurface commutator
If burned areas are caused by eccentricity, mount arma-
ture on its bearings (not on shaft centers), and check concentricity.
Eccentricity should not exceed 0.0002 inch bar-to-bar or 0.001 inch
If test indicates eccentric commutator, resurface
(3) Check soldering between commutator and conductors on arma-
If "solder throwing" is indicated, resolder armature before
(4) If generator armature is in good condition, bake it in dry
oven from 2 to 4 hours at 193F (89.5C) to remove all traces of