Chevrolet 10 Series 1970 Service Manual page 404

ENGINE-ELECTRICAL 6Y-12
4. Disconnect the F -R
D elcotron.
5. Connect the jum per w ire between D elcotron " F " and
battery term in als.
6. Connect the battery ground cable at the battery.
7. Connect an adjustable carbon p ile a cro ss the battery
posts.
8. Start the engine and slow ly bring the speed to 1500
rpm and at the sam e tim e adjust the carbon pile
load to hold the voltage at 14 volts.
9. Read the am perage and com pare with a specifications
chart.
10. Turn o ff ignition, disconnect battery ground cable,
and rem ove all test equipment.
11. If the D elcotron m eets the test sp ecification s, the
problem is not in the gen erator.
12. If the D elcotron fa ils to m eet the test specifications,
rem ove it and p e rfo rm bench tests and make rep a ir
needed.
Delcotron Diode and Field Test (Fig. 8c)
NOTE: These tests w ill indicate good, shorted
o r open fie ld or shorted diode but w ill not in­
dicate a failed open diode.
and follow ing tests show good, r e fe r to s e rv ic e
operations to determ ine cause and rep a ir.
1. Disconnect battery ground cable at battery.
2. P o s itiv e diodes (T e s t A ) —connect an ohm m eter b e­
tween " R " term in al and " B A T " term in al and note
reading, then r e v e r s e the leads at same term in als
and note this reading. M eter should read high r e ­
sistance in one d irection
3. N egative diodes (T e s t B) — connect ohm m eter between
" R " term in al and " GRD"
r e v e rs e the leads and
should read high in one direction and low in the
other.
NOTE: A high or low reading in both d irection s
indicates a d e fective diode.
4. Open F ield Check:
a. Connect an ohm m eter
term in al connector at the
If output was low
and low in the other.
and note reading, then
note this reading. M eter
fro m " F " term inal to
" GRD" term in al stud and note reading on the
low est range scale.
ohms.
b. If m eter reads z e ro o r e x c e s s iv e ly high r e s is t­
ance the D elcotron is faulty.
5. If above tests indicate a d efective D elcotron, rem ove
and com pletely check D elcotron as outlined under
" S ervice O perations."
Indicator L a m p /In itia l Field Excitation Circuit Tests
5 .5 " -6 .2 " Systems
On standard m odels the indicator lamp circu it p rovides
in itial field excitation (causing lamp to glow ). The light
is can celled by closing the fie ld re la y which applies
battery voltage to both side o f bulb (bulb goes out).
The indicator light should glow when ignition switch
is " O N " and go out alm ost im m ediately when engine
starts.
A m m eter equipped veh icles use the same initial field
excitation and control circu its as the indicator lamp
except the lamp is om itted. The continuity tests on both
type veh icles can be made as follow s:
If Lam p F a ils to Glow or A m m eter F a ils to Function
the P o ssib le Causes are:
1. Faulty bulb or bulb socket.
2. Faulty am m eter.
3. An open circu it in w irin g, regu lator, or field .
4. A shorted positive diode - (m ay also cause glow
with ignition switch " O F F " ).
Test as Follows:
1. Disconnect connector from regu lator and turn ign i­
tion switch to " O N" .
connector term inal " 4" to ground (fig . 9c, Step 1)
and note lamp.
a. Lamp fa ils to glow - check fo r faulty bulb, socket
o r open circu it between switch and regulator
connector. R ep air as needed.
b. Light goes on - failu re is in regu lator, D elcotron,
or w ire between " F " term in a ls on regulator and
D elcotron. Go to Step 2.
2. Disconnect lamp lead at ground end and connect
between connector " F " and " 4" term in a ls (fig. 9c,
Step 2), and note lamp:
a. T e s t lamp glow s - p rob lem
open circu it in regu lator or rela y is stuck closed.
See " S ervice O perations" fo r rep a ir.
b. F a ils to glow - problem is in w ire between " F "
term in a ls on gen erator and regu lator o r in field
windings. Go to Step 3.
3. Disconnect test lamp at connector " F " term in al and
connect to " F " term in al
Step 3), and note lamp:
a. Lamp glow s - an open circu it in w ire between
" F " term in als - c o r r e c t as needed.
b. F a ils to glow - D elcotron fie ld has open circu it,
see " S ervice O perations" to rep a ir.
NOTE: This test lamp procedure may be used
on lamp type circu its and on am m eter circu its.
If Lamp F a ils to Go Out, o r i f A m m eter Shows D is­
charge the P o ssib le Causes are:
1. L oose d rive belt - adjust as n ecessary.
2. Faulty field rela y - (see re la y test and adjustment).
3. D efective D elcotron - (see
4. A t norm al idle - p a ra lle l resistance w ire open (See
M eter should read 7 to 20
Connect a test lamp from
is in regu lator. An
on D elcotron (fig. 9c,
D elcotron output test).
CHEVROLET TRUCK SERVICE MANUAL