Cleaning, Inspection and Repair

switch, and fully charged, 24-volt battery in series with

7-4, following the sequence indicated by the key numbers.

each other and connect the group between the field and

Reassembly in reverse sequence.

armature terminals of the generator. Close the battery

switch and adjust the field rheostat for a reading of 28.5

7-10. Cleaning, Inspection and Repair

volts on the volt meter. The ammeter should indicate

a. Clean all metal parts in an approved cleaning

between 1.07 and 1.27 amperes. If the current does not

solvent and blow dry with compressed air.

fall within this range, inspect the generator field frame for

defective terminals, terminal insulation, internal

b. Clean the generator field frame with a soft cloth

connections, or field windings.

dampened in an approved cleaning solvent and wipe dry.

(2) Motoring test. Connect a jumper from the

field terminal to the generator field frame. Connect a

c. Blow all dust and dirt from the armature.

fully-charged, 24-volt battery and a battery switch in

series with each other and connect the group between the

armature terminal and the generator field frame of the

d. Inspect the field frame, commutator end frame,

generator. Close the battery switch. The generator

and drive end frame for cracks and breaks.

armature should revolve in a clockwise direction as

viewed from the drive end. If the armature does not turn

e. Inspect the armature for separated commutator

freely in the correct direction, inspect the generator for

bars and burning.

incorrect assembly, defective bearings, poor brush

contact, or a defective armature.

f. Inspect the ball bearings for roughness and wear.

(3) Output test. Mount the generator on a test

bench and couple it to a drive motor. Connect a field

g. Turn a burned or scored commutator on a lathe

rheostat between the field terminal and the generator field

until the surface is clean and on cneter, and undercut the

frame. Connect the negative terminal of a fully-charged

mica.

battery to the generator and connect the positive terminal

to one terminal of a reverse current relay. Connect the

h. Replace all defective parts in the generator.

other terminal of the relay to the armature terminal of the

generator. Connect a carbon pile rheostat across the

battery.

Momentarily connect a jumper across the

7-1 1. Testing

terminals of the reverse current relay to polarize the

a. Brush Holder Testing.

generator. Start the drive motor and adjust its speed to

1,900 rpm. Adjust the field rheostat for a reading of 28.5

volts on the voltmeter and adjust the carbon pile rheostat

(1) Using a circuit test lamp, test between the

until the ammeter shows a load of 18 amperes. Adjust

insulated brush holder and the commutator end frame. If

the field rheostat as necessary to maintain the voltage.

the lamp lights on this test, the brush holder is grounded

Operate the generator for 15 minutes to attain operating

and the commutator end frame must be replaced.

temperature. Adjust the voltage and amperage to the

(2) Test between the grounded brush holder

above mentioned values. If the rated voltage and

and the commutator end frame. If the lamp fails to light

amperage cannot be maintained, disassemble and

on this test, the brush holder is not grounded and the

overhaul the generator.

commutator end frame must be replaced.

c. Armature and field wiring testing.

Test the

BenchTesting.

armature and field windings of the generator as described

in TM 5-764.

(1) Field current draw. Connect a dc voltmeter

between the field terminal and armature terminal of the

generator. Connect an ammeter, field rheostat, battery

7-5