GMC C Series 1993, Repair Manual

Page: 217 / 264

6P1-6 21-SI 200 GENERATOR
Figure 7—21 -SI Slip Ring End Frame with Stator
i Removed
8. Rotor slip rings. If the rings are dirty, clean with
400 grain or finer polishing cloth.
• Spin the rotor, and hold the polishing cloth
against the slip rings until they are clean.
N O T IC E : T h e r o to r m u s t b e ro ta te d s o th a t
th e s lip rin g s w ill b e c le a n e d e v e n ly . C le a n -
in g th e s lip rin g s b y h a n d w ith o u t s p in n in g
th e r o to r m a y re s u lt in fla t s p o ts o n th e s lip
rin g s , c a u s in g b ru s h n o is e .
— Slip rings that are rough or out of round
should be trued in a lathe to 0.05 mm (0,002
inch) maximum indicator reading. Remove
only enough material to make the rings
smooth and round. Finish the rings with 400
grain or finer polishing cloth and blow away
all dust. ' •
— Test the rotor and stator windings electrically
as described later under “Electrical Tests.”
9. Drive end housing for damage.
10. Slip ring end housing for damage.
ELECTRICAL TESTS
■ 1 i
Except as stated, make the following tests with an
ohmmeter on the low range scale. %
ROTOR FIELD WINDING CHECKS |
m
The rotor may be checked electrically with a 110-volt
test lamp or an ohmmeter (figure 8).
Open Circuit
To check for opens, connect the test lamp or ohmme­
ter to each slip ring. If the lamp fails to light, or if the
ohmmeter reading is high (infinite) the winding is open.
Short Circuit or Resistance Check
The winding is checked for Short-circuits or excessive
resistance by connecting
a
12-volt battery and ammeter
in series with the edges of the two slip rings. Note the
ammeter reading and refer to “Specifications.” 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. If
the resistance reading is below the value given in
"Specifications” at the end of this section, the winding
has excessive resistance.
The winding resistance and ammeter readings will
vary slightly with winding temperature changes. If the
rotor is all right but the generator fails to supply rated
output, the problem is in the diode trio, rectifier bridge,
stator, or regulator. To check for grounds, connect the
ohmmeter as shown. Replace the rotor if the reading is
less than infinite. >
If the rdtor checks are not within specifications,
replace the rotor.