Stator

CAUTION

Do not touch test probes to polished

mating surfaces.

(1) Rotor. Refer to figure 3-2 and perform the

following checks:

(a) Grounds. Connect 1 10-volt test

lamp or an ohmmeter from either slipring to the rotor

shaft or to the rotor poles. If the lamp lights, or if

ohmmeter reading is low, it indicates the field is

grounded.

(b) Open windings. Connect test lamp

or ohmmeter to each slipring and if lamp fails to light or if

ohmmeter reading is high (infinite), winding is open.

and ohmmeter in series with two sliprings. Note the

ammeter reading. If reading is above 1.9-to 2.3ohms, it

indicates shorted windings.

(d) Field resistance.

Connect an

ohmmeter to the two sliprings and check the resistance

of the field. If the resistance reading is below 1.9-to

2.3ohms, the winding is shorted. Replace a defective

rotor as required.

(2) Stator. Refer to figure 3-2 and perform

following checks:

(a) Ground. Check stator windings with

a 110-volt test lamp or an ohmmeter. If the test lamp

lights, or if the meter reading is low when connected from

any stator lead and to the frame, the windings are

grounded.

Figure 3-3. Checking heat sink diodes.

(b) Open windings. Connect test lamp

or ohmmeter to any stator lead and to the frame. The

(a) Ohmmeter method.

Use an

windings are open if the lamp fails to light or if the meter

ohmmeter with a 11/2-volt cell and use the lowest range

reading is high when successively connected between

scale.

each pair of stator leads.

Replace stator having

Disconnect stator from the heat sink diodes.

grounded or open windings.

1. Connect one ohmmeter lead to the

NOTE

heat sink and the other one to the diode lead and note

Due to low resistance of the stator

the reading. Reverse the ohmmeter lead connections

windings, it is difficult to locate a

and check the reading.

short circuit in the windings, without

2. If both readings are either very low

the use of laboratory test equipment.

or very high, the diode is defective. A good diode is

Shorted Stator windings are indicated

indicated by one low reading and one high reading.

if all other electrical checks are

Check the two remaining heat sink diodes in same

normal but alternator does not supply

manner.

rated output.

3. Check the end frame diodes in the

(3) Diodes. Refer to figure 3-3 and check

same manner as the heat sink diodes. However,

each diode electrically for a shorted or open condition by

connect

any one of the following methods:

3-3