GMC 1976 ZEO 6083 Maintenance Manual page 406

6Y- 26 ENGINE ELECTRICAL
test between the single connector and each of the
other two connectors . Also, connect the ohmmeter
to each pair of the three connectors (not illustrated) .
If any reading is zero, replace the diode trio .
RECTIFIER BRIDGE CHECK
Note that the rectifier bridge has a grounded heat
sink and an insulated heat sink connected to the
output terminal .
To check the rectifier bridge, connect the ohmm-
eter to the grounded heat sink and one of the three
terminals, (figure 30). Connect to flat metal connec
tor, and not onto threaded stud . Then reverse the
lead connections to the grounded heat sink and same
terminal . If both readings are the same, replace the
rectifier bridge . A good rectifier bridge will give one
high and one low reading. Repeat this same test
between the grounded heat sink and the other two
terminals, and between the insulated heat sink and
each of the three terminals. This makes a total of six
checks, with two readings taken for each check.
The ohmmeter check of the rectifier bridge, and
of the diode trio as previously covered, is a valid and
accurate check. Do not replace either unit unless at
least one pair of readings is the same .
CAUTION: Do not
use high voltage to check
these
units such
as a 110
volt test
lamp.
To replace the rectifier bridge, remove the attach-
ing screws, and disconnect the capacitor lead . Rec-
tifier bridges may vary in appearance but are
completely interchangeable in these generators .
BRUSH
HOLDER
CONNECT TO FLAT
METAL AND NOT
TO THREADED STUD
OHMMETER
Figure 30-Rectifier Bridge Check
STATOR CHECKS
The stator windings may be checked with a 110-
volt test lamp or an ohmmeter. If the lamp lights, or
if the meter reading is low when connected from any
stator lead to the frame, the windings are grounded .
NOTE : Delta windings on 80-amp . generator
cannot be checked for opens.
A short circuit in the stator windings is difficult
to locate without laboratory test equipment due to
the low resistance of the windings . However, if all
other electrical checks are normal and the generator
fails to supply rated output, shorted stator windings
or an open delta winding on 80-amp . generator is
indicated . Also, a shorted stator can cause the indica-
tor lamp to be on with the engine at low speed.
BRUSH HOLDER AND REGULATOR
REPLACEMENT
After removing the three attaching nuts, the sta-
tor, and diode trio screw (figure 30) the brush holder
and regulator may be replaced by removing the two
remaining screws . Note the two insulators located
over the top of the brush clips in Figure 26, and that
these two screws have special insulating sleeves over
the screw body above the threads. The third mount-
ing screw may or may not have an insulating sleeve .
If not, this screw must not be interchanged with
either one of the other two screws, as a ground may
result, causing no output or uncontrolled generator
output . Regulators may vary in appearance but are
completely interchangeable in these generators .
SLIP RING SERVICING
If the slip rings are dirty, they may be cleaned
and finished with 400 grain or finer polishing cloth.
Spin the rotor, and hold the polishing cloth against
the slip rings until they are clean.
CAUTION:
The
rotor must
be rotated
in or-
der
that the slip
rings will
be cleaned evenly.
Cleaning the slip
rings
by hand without
spinning
the rotor
may
result
in flat spots on
the slip
rings, causing
brush noise.
Slip rings which are rough or out of round should
be trued in a lathe to .002 inch maximum indicator
reading. Remove only enough material to make the
rings smooth and round. Finish with 400 grain or
finer polishing cloth and blow away all dust .
BEARING REPLACEMENT AND
LUBRICATION
The bearing in the drive end frame can be