Chevrolet 1977 light duty truck, Service Manual

Page: 598 / 861

as stamped on generator frame, generator is not defective;
recheck Steps l through 5.
g. If ampere output is not within 10 percent of rated
output, ground the field winding by inserting a screwdriver
into the test hole (Fig. 6D-4C).
CAUTION: Tab is within 3 /4 inch (19m m ) o f
casting surface. D o n o t force screwdriver deeper
than one inch (25m m ) into end frame.
h. O perate engine at m oderate speed as required, and
adjust carbon pile as required to obtain maximum current
output.
i. If output is within 10 percent of rated output, replace
regulator as covered in the Chassis Overhaul M anual and
check field winding.
j. If output is not within 10 percent of rated output,
check the field winding, diode trio, rectifier bridge, and stator
as covered in the Chassis Overhaul Manual.
k. Remove am m eter from generator and turn accessories
off.
O V E R C H A R G E D B A T T E R Y C O N D I T I O N C H E C K
1. Determ ine battery condition. Test is not valid if
battery is not good and fully charged.
2. Connect a voltm eter from generator No. 2 term inal
to ground. If reading is zero, No. 2 lead circuit is open.
3. If battery and No. 2 lead circuit check good, but an
obvious overcharge condition exists as evidenced by excessive
battery w ater usage, proceed as follows:
a. Separate end frames as covered in generator
"Disassembly" section in the Chassis Overhaul Manual.
Check field winding for shorts. If shorted replace rotor and
regulator.
b. Connect ohm m eter using lowest range scale from
brush lead clip to end frame as shown in Step 1, Figure 6D-
5C, then reverse lead connections.
c. If both readings are zero, either the brush lead clip
is grounded, or regulator is defective.
d. A grounded brush lead clip can result from omission
of insulating washer (Fig. 6D-5C), omission of insulating
sleeve over screw, or damaged insulating sleeve. Remove
screw to inspect sleeve. If satisfactory, replace regulator as
covered in the Chassis O verhaul Manual.
G E N E R A T O R O U T P U T T E S T
To check the generator in a test stand, proceed as
follows:
1. Make connections as shown in Figure 6D-6C, except
leave the carbon pile disconnected. Use a fully charged
battery and a 10 ohm resistor rated at six watts or more
between the generator No. 1 term inal and the battery.
2. Slowly increase the generator speed and observe the
voltage.
3. If the voltage is uncontrolled with speed and increases
above 16 volts, check for a grounded brush lead clip as
covered under heading of "O V E R C H A R G E D BA TTERY ",
Step 3. If not grounded, replace the regulator.
NO TE:
The battery must be fully charged when making
this check.
Fig. 6 D -5 C -S lip Ring End Frame
4. Connect the carbon pile as shown.
5. Operate the generator at moderate speed as required
and adjust the carbon pile as required to obtain maximum
current output.
6. If output is within ten percent of rated output as
stamped on generator frame, generator is good.
7. If output is not within ten percent of rated output,
ground generator field (Fig. 6D-4C).
8. O perate generator at m oderate speed and adjust
carbon pile as required to obtain maximum output.
9. If output is within ten percent of rated output, replace
regulator as covered in "Regulator Replacement" section.
10. If output is not within ten percent of rated output,
check the field winding, diode trio, rectifier bridge and stator
as previously covered.
O T H E R H A R N E S S C H E C K S
Wires in the charging system may be checked for
continuity by us of an ohm m eter or a test light (12 volt).
Connect the test so the wire in question is in series in in the
test circuit.
CAPACITOR
RECTIFIER
BRIDGE
DIODE
ATTACHING TRI°
NUTS
INSULATING
WASHERS
OHMMETER
RESISTOR