Chevrolet 70 1969 Series, Shop Manual

Page: 730 / 913

E N G IN E ELECTRICAL 6Y-15
(CHECK FOR GROUNDS)
O H M M ET ER
OHMMETER
(CHECK FOR SHORTS AND OPENS)
Figure 5 — C h e c k in g for G ro u n d e d , Sh orted, or O p e n Circuit in Rotor
U sin g O h m m e te r
BEN CH -TESTIN G G E N E R A T O R
C O M P O N E N T S
ROTOR CHECKS
Rotor m ay be checked for grounded wiring either by
use of test lam p or with an ohmmeter.
Checking for G round With Test Lam p. Touch one test
lamp lead to one of the slip rings and other lead to rotor
pole or shaft. If lamp lights, the windings are grounded
and rotor assembly must be replaced.
Checking for Ground with O h m m ete r (fig. 5). M ak e
test in same m anner as with test lamp and observe read­
ing. If reading is low, indicating low resistance, the wind­
ing is grounded and rotor assembly m ust be replaced.
Checking for Open Circuit W ith Test L a m p or O h m ­
meter (fig. 5). Touch the leads from lam p or ohm m eter to
each of the slip rings. If lam p fails to light or if ohm meter
reading is high (infinite), the winding is open.
Checking for Shorted Winding in R otor Assembly.
Either of two methods m ay be used to check rotor wind­
ing for shorts as described below:
1. A m m eter and Battery M ethod. Connect 12-volt bat­
tery and am m eter in series with the two slip rings.
Note am m eter reading. If reading is over 2.6 a m ­
peres, there is a short circuit in winding.
2. O h m m eter M ethod. Connect ohm m eter leads to the
two slip rings and note the resistance reading. If the
resistance is less than 4.6 ohms, there is a short cir­
cuit in rotor winding.
NOTE: If an ohmmeter is not available, the res­
istance can be calculated by dividing the vol­
tage by the current (amperes) using values
from Step 1 above.
OHMMETER OHMMETER
(Check for Open Circuit) (Check
fo r
Open Circuit)
OHMMETER
(Checking for
Ground)
Figure 6 — C h e c k in g for G r o u n d e d or O p e n Circuit in Stator W in d in g s
U sin g O h m m e te r
directed in “ Generator O utput Test” trouble is in either
the stator assembly or in the rectifying diodes.
STATOR CHECKS (Fig. 6)
With stator assembly separated from end frames and
all leads disconnected, the stator assembly m ay be tested
for grounds, open circuits, or shorted windings as directed
below:
1. Connect one of the leads from t e s t ‘lamp or an o h m ­
meter to any one of the three stator leads, and touch
the other lead to the stator frame. If the lamp lights
or if ohm m eter reading is low, the stator windings are
grounded.
2. C o n n e d test lamp leads or ohm meter leads success­
ively between pairs of stator winding leads (fig. 6); if
lamp fails to light or if ohm m eter reading is high, an
open circuit is indicated in stator.
OHMMETER OHMMETER
(C h e c k in g C a p a c it o r) (C h e c k in g D iode)
If there are no defects found in the rotor assembly and
generator does not produce rated output when checked as
Figure 7 — Te stin g D io de s a n d C a p a c ito r
CHEVROLET SERIES 70-80 H EAVY DUTY TRUCK SH O P M A N U A L