GMC 1976 ZEO 6083 Maintenance Manual page 405

3. Loosen bolt in adjusting arm and mounting
bracket. Move generator to loosen drive belt (or
belts); remove belt(s) from generator pulley .
4. Remove the bolt attaching the generator to
mounting bracket, remove adjusting arm bolt, then
remove generator from engine.
GENERATOR REPAIR
To repair the generator, observe the following
procedure :
DISASSEMBLY (FIGURE 28)
To disassemble the generator, take out the four
thru-bolts, and separate the drive end frame and ro-
tor assembly from the stator assembly by prying
apart with a screwdriver at the stator slot . A scribe
mark will help locate the parts in the same position
during assembly . After disassembly, place a piece of
tape over the slip ring end frame bearing to prevent
entry of dirt and other foreign material, and also
place a piece of tape over the shaft on the slip ring
end. If brushes are to be reused, clean with a soft dry
cloth .
CAUTION: Use pressure sensitive tape and
not friction tape which would leave a
gummy deposit on the shaft.
To remove the drive end frame from the rotor,
place the rotor in a vise and tighten only enough to
permit removal of the shaft nut. CAUTION: Avoid
excessive tightening as this may cause distortion of
the rotor. Remove the shaft nut, washer, pulley, fan,
and the collar, and then separate the drive end frame
from the rotor shaft.
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 (figure 28). Connect test lamp or
ohmmeter from one slip ring to shaft . If lamp lights,
or reading is low, the rotor winding is grounded.
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.
Note the ammeter reading and refer to Generator
Specifications. An ammeter reading above the speci-
fied value indicates shorted windings; a reading be-
low 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
ENGINE ELECTRICAL
6Y- 2 5
(figure 28). If the resistance reading is below the
specified value, the winding is shorted; if above the
specified value the winding has excessive resistance .
The specified resistance value can be determined
by dividing the voltage by the current given in Gen-
erator Specifications . Remember that the winding
resistance and ammeter readings will vary slightly
with winding temperature changes. If the rotor is not
defective, but the generator fails to supply rated out-
put, the defect is in the diode trio, rectifier bridge or
stator .
DIODE TRIO CHECK
The diode trio is identified in Figure 26 . First,
connect an ohnuneter using lowest range scale from
diode trio long connector to end frame as shown in
Step 2, Figure 26, then reverse lead connections. If
both readings are the same, check for grounded
brush lead clip caused by omission of insulating
washer (figure 26), omission of insulating sleeve over
screw, or damaged insulating sleeve . Remove screw
to inspect sleeve . If screw assembly is correct, and both
ohmmeter readings are the same, replace regulator.
To check the diode trio, remove it from the end
frame assembly by detaching the three nuts, the at-
taching screw, and removing the stator assembly .
Note that the insulating washer on the screw is as-
sembled over the top of the diode trio connector.
Connect an ohmmeter having a 1-1/2 volt cell, and
using the lowest range scale, to the single connector
and to one of the three connectors (figure 29). Ob-
serve 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
Figure 29-Diode Trio Check