To remove the drive end frame from the rotor, place the
fails to supply rated output, the defect is in the diode
rotor in a vise and tighten only enough to permit
trio, rectifier bridge, stator, or regulator.
removal of the shaft nut.
Diode Trio Check
tightening as this
trio, remove it from the end frame assembly by
distortion of the rotor.
detaching the three nuts, the attaching screw, and
removing the stator assembly.
Remove the shaft nut, washer, pulley, fan, and the
collar, and then separate the drive end frame from the
Rotor Field Winding Checks
To check for opens, connect the test lamp or ohmmeter
to each slip ring. If the lamp fails to light, or if the
ohmmeter reading is high (infinite), the winding is open
(Fig. 8). Connect test lamp
or ohmmeter from one slip
ring to shaft. If lamp lights, or if reading is low, the rotor
winding is grounded (not illustrated).
The winding is checked for short-circuits or excessive
resistance by connecting a battery and ammeter in
series with the edges of the two slip rings.
Fig. 9 - View Inside End Frame.
That the insulating washer on the
screw is assembled over the top of
the diode trio connector.
Connect an ohmmeter having a 1l volt cell, and using
the lowest range scale, to the single connector and to
one of the three connectors (Fig. 10). Observe the
reading. Then reverse the ohmmeter leads to the same
two connectors. If both readings are the same, replace
the diode trio. A good diode trio will give one high and
one low reading. Repeat this same test between the
single connector and each of the other two connectors.
Also, connect the ohmmeter to each pair of the three
Fig. 8 - Checking Rotor.
connectors (not illustrated). If any reading is zero,
replace the diode trio.
The ammeter should indicate a reading of from 4.0 to
5.0 amperes. An ammeter reading above the specified
value indicates shorted windings; a reading below the
specified value indicates excessive resistance. An
alternate method is to check the resistance of the field
by connecting an ohmmeter to the two slip rings (Fig.
If the resistance reading
is below the specified
value, the winding is shorted; if above the specified
value the winding has excessive resistance.
specified resistance value should be from 2.5 to 3.0
Remember that the winding resistance and ammeter
Fig. 10 - Testing Diode Trio.
readings will vary slightly with winding temperature
changes. If the rotor is not defective, but the alternator