GMC C Series 1993, Repair Manual

Page: 218 / 264

21 -SI 200 GENERATOR 601 -7
DIODE TRIO CHECK
Use an ohmmeter with a 1.5-volt cell and set it to the
lowest range scale. Place the negative ohmmeter lead
on the regulator strap and use the positive lead to
check for continuity to each of the three rectifier bridge
straps (figure 9).
All three readings should indicate continuity. Reverse
the ohmmeter leads and perform the checks. Readings
should all indicate open circuits. If any reading is
wrong, replace the diode trio;
RECTIFIER BRIDGE CHECK
To check the rectifier bridge, connect the ohmmeter to
the grounded heat sink and one of the three flat metal
connectors (figure 10). Do not bend the flat metal clips.
Observe the ohmmeter reading and reverse the lead
connections to the grounded heat sink and the same
flat metal connector. A good rectifier bridge will give
one high and one low reading. If both readings are the
same, replace the rectifier bridge. Repeat this same test
between the grounded heat sink and the other two con­
nectors, and between the insulated heat sink and each
of the three connectors. 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.
STATOR CHECKS
The stator windings may be checked with a 110-volt
test lamp or an ohmmeter (figure 11). If the lamp lights,
or if the meter reading is low when connected from any
stator lead to the frame, the windings are grounded.
Refer to the specifications at the end of this section.
Replace the stator. .
An open or a short circuit in the delta 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 produce within 15 amps of the rated output,
shorted or open delta windings are indicated, and the
stator should be replaced. . . . . . .
TESTING THE REGULATOR
1. Connect the voltmeter and. fast charger to the
12-volt battery (figure 12).
2. Connect the regulator and test lamp as shown.
Observe battery polarity.
3. The test lamp should be on.