Chevrolet 70 1969 Series, Shop Manual

Page: 731 / 913

E N G IN E ELECTRICAL 6 Y -16
3. A short circuit in the stator windings is difficult tc lo­
cate without laboratory test equipment due to low res­
istance of the windings. However, if generator out-put
is below specified rating and none of the other tests
show defects in other units, shorted stator windings
are indicated. When defective stator windings are
found, the complete stator assembly must be replaced.
DIODE CHECKS (Fig. 7)
Each of the six diodes m ay be checked electrically for a
shorted or an open condition, using either of the methods
described below. Stator leads m ust be disconnected and
lead from diode being tested must not be in contact with
lead from other diode.
Checking Diodes With O hmm eter. To check diodes
with ohmmeter, use lowest range scale and use 1 - 1/2
volt cell in ohmmeter.
Connect one lead from ohm m eter to diode lead and
other lead to diode case and note reading on ohm meter
(fig. 7). Reverse the ohm m eter lead connections and note
reading. If both readings are very low or if both readings
are very high, the diode is defective. A good diode will
show one low reading and one high reading. Repeat fore­
going procedure to check each diode.
NOTE: All diodes, if in good condition, will
show one high reading and one low reading,
but the respective reading at diodes in heat
sink will be opposite from those in end frame
assembly.
Checking Diodes With Test Lamp. An alternate m eth­
od of checking diodes is to use a test lam p of not more
than 12 volts in place of an ohmmeter.
C AU TIO N : Do not use 110-volt test lam p to
check diodes.
With stator leads disconnected, connect the test lamp
leads across each diode in same manner as previously
given for checking with ohm meter. First check for current
flow in one direction, then in reverse direction. If the test
lamp lights in both checks, or fails to light in both checks,
the diode is defective. When checking a good diode, the
test lamp will light only when connected in one direction.
Special Testers. Special testers are available which op­
erate without disconnecting stator. W hen using this type
of equipment, follow m anufacturer’s recommendations.
CAPACITOR CHECK
The capacitor (fig. 7) is pressed into retainer in genera­
tor end frame and capacitor lead is connected to heat
sink.
Sincc the capacitor rating is only 0.5 microfarads, it is
impractical to test the capacitance with conventional
equipment; however, when generator is disassembled for
overhaul, a check should be made to be sure the insula­
tion between elements is not permitting a current leak to
ground.
Check can be m ade with 12-volt test lamp or a II - 1/2
2 Retainer and Seal Assy.
5
Shield
3 Gasket 6 Outer Spacer
4 Bearing Assy. 7 Drive End Frame
Figure 8 — Drive End Fram e a n d B e a r in g C o m p o n e n ts
- volt ohmmeter. Connect one test lead to capacitor lead
and other lead to condenser case (fig. 7). Wiggle the “ pig
tail” lead while observing o hm m eter or test lamp. If capa­
citor is good, the ohm m eter will show infinite (high) resis­
tance or a test lamp will not glow during test.
Any capacitor which allows current leakage as indicat­
ed by low ohm m eter reading m ust be replaced. Capacitor
replacement is covered under “ Mechanical Inspection and
Repair” in this section.
M E C H A N IC A L IN SP EC T IO N A N D REPAIR
INSPECTION
In addition to the testing procedures for checking elec­
trical circuits through various units, an inspection of all
parts should be m ade to determine their condition. Clean
all parts except bearing assemblies, which should not be
washed as they are packed with special lubricant.
1. Check drive end frame and bearing assembly for con­
dition of bearing, felt seal, and retainer (fig. 8). Ex­
amine end frame for cracks and for dam aged threads.
2. Rotor assembly should be inspected for scoring at slip
rings (fig. 17) and at surfaces contacted by shaft bear­
ings. If shaft is damaged, a new rotor assembly
should be installed at assembly. Procedure for resur­
facing slip rings is given later under “ Repair.”
3. Inspect brushes, brush springs, and brush holder at­
tached to slip ring end frame assembly. If brushes are
worn to half their original length or are dam aged they
must be replaced. Visually inspect brush springs; if
springs are distorted, worn, or broken, replace with
new springs.
4. Inspect rotor shaft bearing in slip ring end frame. If
there is evidence that bearing has been run without lu­
bricant, or if bearing is not in good condition, it must
be replaced as directed in “ Repair.”
REPAIR
Drive End Frame Bearing Replacement (Fig. 8)
With generator disassembled into major components,
proceed as follows to replace bearing assembly in drive
end frame. Key numbers in text refer to figure 8.
CHEVROLET SERIES 70-80 H EAVY DUTY TRUCK S H O P M A N U A L