C703/C703A and C706 Alternators
C.E. Niehoff & Co.
Before troubleshooting any CEN products, the service technician should:
WARNING
• read, understand, and agree to follow all information contained in this troubleshooting guide.
• understand the operational characteristics of the electrical charging system components to be tested.
• be profi cient at the use of tools and test equipment used in troubleshooting CEN products.
Troubleshooting Guide
Hazard Definitions
These terms are used to bring attention to presence of hazards
of various risk levels or to important information concerning
product life.
Indicates presence of hazard(s) that
WARNING
can cause severe personal injury,
death, or substantial property
damage if ignored.
Indicates presence of hazards that
CAUTION
will or can cause minor personal
injury or property damage.
Table of Contents
Section A: Description and Operation ....................... 2-3
Section B: Schematic Diagram .................................... 4
Section C: On-Vehicle Troubleshooting ..................... 5-7
Tools and Equipment
• Digital Multimeter (DMM)
• Ammeter (digital, inductive)
• Jumper wires
• CEN 6-pin Inline Harness Test Tool A10-114
Figure 1—CEN 6-pin Inline Harness Test Tool A10-114
Testing Guidelines
Professional service technicians rely on the following
guidelines when testing electrical components.
Voltage testing:
• Set meter to proper scale and type (AC or DC).
• Be sure to zero the meter scale or identify the meter
burden by touching meter leads together. Meter burden must be subtracted from final reading obtained.
• Be sure the meter leads touch source area only.
Prevent short circuit damage to test leads or source
by not allowing meter leads to touch other pins or
exposed wires in test area.
• Be sure to use CEN tools designed especially for
troubleshooting CEN alternators when available.
See page 1 for more information.
Resistance (ohm) testing:
• Set meter to proper scale.
• Be sure to zero the meter scale or identify the meter
burden by touching meter leads together. Meter burden must be subtracted from final reading obtained.
• Be sure the meter leads touch source area only.
Prevent altering the reading by not allowing fingers
or body parts to touch meter leads or source during
reading.
• Be sure reading is taken when source is at 70ºF.
Readings taken at higher temperatures will increase
the reading. Conversely, readings taken at lower
temperatures will decrease the reading.
• Be sure to test directly at the source. Testing through
extended harnesses or cable extensions may increase
the reading.
Voltage drop testing:
• Measure voltage between B+ on alternator or source
and B- (ground) on alternator or source. Record
obtained reading. Move to batteries or other source
and measure again between B+ and B- terminals on
battery or other source. Difference between the two
readings represents voltage lost within the circuit
due to but not limited to inadequate cable gage or
faulty connections.
• Voltage drop measurements must be taken with
all electrical loads or source operating.
Dynamic/Live testing:
Definition: Connecting power and ground to a
component to test operation/function out of circuit.
1. Be sure to connect jumper leads directly and securely
to source contacts of the component being tested.
2. Be sure to make any connection to power and ground
at the power supply or battery source terminals. Do
not make connection at component source terminals
as that may create an arc and damage component
source terminals.
TG31K
Page 1
Section A: Description/Operation
CEN C703/C703A and C706 Alternators/Regulators Description and Operation
C703/C703A 28 V (350 A) and C706 28 V (300 A) alternators are internally rectified. All windings and currenttransmitting components are non-moving, so there are no brushes or slip rings to wear out.
These alternators are externally energized when the battery master switch on the vehicle is turned on and provides
power to the regulators through the IGN circuit (the A2-341 regulator can also operate without vehicle connection to
IGN, and instead provide power by sensing rotation through the regulator’s AC circuit).
Field coil is then energized. AC is rectified into DC output through diodes in drive end rectifier housing and supplied
to the battery from the alternator B+ terminal. See schematic diagram on page 4. Alternator output current is selflimiting and will not exceed rated capacity of alternator. Regulator maintains alternator output voltage at pre-determined
regulated setting (see Table 1 or 2 below for setpoints) as vehicle electrical loads are switched on and off.
Battery type selection and battery maintenance/function are the sole responsibilities of the customer.
A2-214 and A2-325 regulators furnished with some units include:
• External IGN terminal for energize connection.
• P terminal that can provide optional AC voltage tap. P terminal signal frequency (Hz) x 10 = alternator shaft rpm.
• D+ terminal that can provide DC voltage signal to vehicle electrical system, confirming alternator operation.
• Overvoltage cutout (OVCO) function. See page 5.
• (A2-214 only) Green-lensed LED. See page 5.
• (A2-325 only) Tricolored LED. See page 5.
• Regulator fixed (flat temperature compensation) setpoints shown in Table 1 are selected based on battery type.
Table 1 — A2-214 & A2-325 Regulator Setpoint Switch Position
Voltage Setpoints (±0.2 V) Battery Type
Position 1 27.5 V Maintenance
Position 2 28.0 V Maintenance
Position 3 28.5 V Maintenance-free
Position 4 29.0 V Maintenance-free
Note on Group 31 batteries: If boiling or excessive gassing occurs with high voltage
setpoint (position 3), change to medium voltage setpoint (position 2).
Figure 2—Voltage Setpoints
A2-341 regulator furnished with some units includes:
• External IGN terminal that can provide optional external energize connection. This regulator can function with or
without vehicle ignition. When necessary, regulator IGN terminal can be connected to vehicle ignition source to provide
battery voltage when engine is running. Circuit should be off (no voltage present) when vehicle ignition is off or engine
is not running.
• P terminal that can provide optional AC voltage tap. P terminal signal frequency (Hz) x 10 = alternator shaft rpm.
• D+ terminal that can provide DC voltage signal to vehicle electrical system, confirming alternator operation.
• Overvoltage cutout (OVCO). See page 6.
• Tricolored LED. See page 6.
• Temperature-voltage sense/J1939 harness connector that can be used with optional harness.
— When optional temperature-voltage sense/J1939 harness is not connected, regulator will operate in fixed voltage
setting determined by the select switch position on the bottom of the regulator. See Column 2 in Table 2.
— When optional temperature-voltage sense/J1939 harness is connected, regulator will automatically optimize the
charge voltage for battery type based on temperature. Also, vehicle manufacturer-requested functions of J1939
interface are available through connector. See Column 3 in Table 2.
Table 2 — A2-341 Regulator Voltage/Battery Switch Position
Switch Position
Page 2
T-VS/J1939 Harness Not
Connected (Voltage Select)
Position 1 27.5 V Maintenance (D Category)
Position 2 28.0 V Maintenance-free (Group 31)
Position 3 28.5 V AGM
Position 4 29.0 V
T-VS/J1939 Harness Connected
(Battery Select)
DO NOT USE POSITION # 4
Figure 3—Voltage/Battery Switch
TG31K
Section A: Description and Operation (CONT’D)
B+ terminal on
back side of
control housing
B– terminal
C703 ADE View
IGN terminal
D+ terminal
B+ bolt
terminal
Figure 4 — C703/C703A Alternator Terminals
(Regulator Attached to Alternator)
C703A ADE View
P terminal
B– terminal
stud
C706 ADE View
P terminal
Figure 5 — C706 Alternator Terminals
(Regulator Attached to Alternator)
D+ terminal
IGN terminal
TG31K
Page 3
Section B: Schematic Diagram
Schematic diagram for C703/C703A and C706 alternators with dual diode trio circuit.
Date code before Sept. 8, 2010 is stamped on DE housing.
STATOR
RECTIFIER
STATOR
*Thermal switch is not factory-
DUAL
DIODE TRIO
installed on all models.
ALTERNATOR
BK
FIELD
BR
W
B+
R
R
F
E
B–
Bñ
D
C
B
A
*
THERMAL
SWITCH
G
IGNITION
SWITCH
CHARGE
WARNING
LIGHT OR
CONTROLLER
IGN
E
A2-212
REGULATOR
BATTERY
D+
P
R
REGULATOR
RECEPTACLE
LOAD
Schematic diagram for C703/C703A and C706 alternators without dual diode trio circuit.
Date code on or after Sept. 8, 2010 is stamped on DE housing.
Page 4
*
BK
R
BR
W
*Thermal switch is not factoryinstalled on all models.
G
Figure 6 — C703/C703A and C706 Schematic Diagrams
TG31K
Section C: On-Vehicle Troubleshooting
REMOTE-MOUNTED REGULATORS:
CHECK CONDITION OF FUSE IN WIRING HARNESS BEFORE TROUBLESHOOTING
A2-214 Regulator Troubleshooting
A2-214 regulator is either attached directly to the
outside of alternator or remote-mounted on the vehicle.
Main diagnostic feature is a green lens LED located on
the front of the regulator. LED indicates whether regulator has been energized. See Table 3 for LED indication
and status.
Regulators with OVCO (overvoltage cutout) will trip at
vehicle electrical system voltages above 32 volts that
exist longer than 3 seconds. OVCO feature detects high
voltage and reacts by signaling the alternator field
circuit to open. This turns off alternator. Restarting
engine resets OVCO circuit. Regulator regains control
of alternator output voltage.
INDICATION STATUS
ON steady Normal regulator operation.
FLASHING Regulator is receiving energize
OFF Regulator is not receiving energize
TABLE 3 — A2-214 Regulator
LED Indications and Status
Alternator is producing output.
signal. LED will fl ash until
alternator produces output.
signal or OVCO has tripped.
A2-325 Regulator Troubleshooting
A2-325 regulator is attached directly to the outside of alternator or mounted remotely on the vehicle.
Main diagnostic feature is a tricolored LED next to the harness receptacle on regulator. LED works like a voltmeter,
measuring charging voltage. See Table 4 for diagnostic features and LED explanations.
Regulators with OVCO (overvoltage cutout) will trip at vehicle electrical system voltage above 32 volts that exists longer
than 3 seconds. OVCO feature detects high voltage and reacts by signaling relay in alternator field circuit to open. This
turns off alternator (LED is flashing RED—some units may flash AMBER). OVCO circuit is reset when engine is restarted.
Regulator regains control of alternator output voltage.
TABLE 4 — A2-325 Regulator Diagnostics with Engine On
LED COLOR STATUS
GREEN Solid
AMBER Solid
Flashing
RED Solid
Flashing
Alternator and regulator operating normally.
Low system voltage — Electrical load exceeds alternator rating at present rotor speed.
(Some models) Alternator fault — No output.
(Some models) OVCO tripped.
High system voltage – May occur during normal load
switching.
OVCO tripped.
No power to ignition or regulator is defective.OFF
ACTION
No action required.
When loads decrease or speed increases, LED
should be solid GREEN. If not, check drive belt
and charging system connections.
Replace alternator.
Overvoltage condition. Attempt reset.
System diagnosis required. Go to page 7.
If flashing more than 3 seconds, OVCO will trip,
disabling charging system. LED will flash RED.
Overvoltage condition. Attempt reset. System
diagnosis required. See OVCO condition in
“General Troubleshooting” section on page 6.
Go to Chart on page 7.
TG31K
Page 5
Section C: On-Vehicle Troubleshooting (CONT’D)
A2-341 Regulator Troubleshooting
Main diagnostic feature is a tricolored LED located on the front of the regulator. LED works like a voltmeter, measuring
charging voltage. See Table 2 for LED diagnostics.
This regulator has OVCO (overvoltage cutout) that will trip at vehicle electrical system voltage above 33 volts that exists
longer than 3 seconds. OVCO feature detects high voltage and reacts by signaling relay in alternator field circuit to open.
This turns off alternator (LED is f lashing RED). OVCO circuit is reset when engine is restarted or can also reset when
system voltage normalizes after 2-minute wait.
An additional temperature-voltage sense/J1939 harness may or may not be used with the A2-341 regulator:
• When optional temperature-voltage sense/J1939 harness is not connected, regulator will operate in fixed voltage
setting determined by the select switch position on the bottom of the regulator.
• When optional temperature-voltage sense/J1939 harness is connected, regulator will automatically optimize the
charge voltage for battery type selected based on temperature. Also, vehicle manufacturer-requested functions of
J1939 interface are available through connector.
TABLE 2 — A2-341 Regulator LED Diagnostics with Engine On*
LED COLOR STATUS
GREEN Solid
Alternator and regulator operating normally.
No action required.
ACTION
AMBER Solid
Flashing*
RED Solid
Flashing
* LED will flash AMBER for one minute upon start-up/shutdown—if regulator does not sense alternator rotation, regulator will time out.
Low system voltage — Electrical load exceeds
alternator rating at present rotor speed.
Alternator fault — No output.*
High system voltage – May occur during
normal load switching.
OVCO tripped.
No power to ignition or regulator is defective.OFF
When loads decrease or speed increases, LED
should be solid GREEN. If not, check drive belt and
charging system connections.
Replace alternator.*
Indicates voltage above setpoint but below OVCO
threshold (less than 33 volts).
Indicates voltage exceeds 33 V for more than
3 seconds. System diagnosis required. See “OVCO
Troubleshooting” section below.
Go to Chart on page 7.
Temperature-Voltage Sense/J1939 Harness Troubleshooting
To verify temperature sense function on T-VS/J1939 harness: Apply a warm air source (such as a hair dryer, not to heat
above 120°F) to battery negative terminal of harness. B+ battery voltage should decrease as temperature increases.
If voltage does not decrease: Check for a resistance reading of 5-15K Ohms across pin H in 10-pin connector on T-VS/
J1939 harness and ground with meter in K Ohm scale. Then check for battery voltage across pin J on T-VS/J1939
harness and ground with meter in VDC scale. If both readings pass, go to chart on page 7. If one or both readings fail,
verify proper terminal connections on B+ and B− terminal leads from T-VS/J1939 harness. If both terminal connections
are good, entire harness is defective and should be replaced.
OVCO Troubleshooting
Shut down vehicle and restart engine. If alternator functions normally after restart, a “no output condition” was normal
response of voltage regulator to “high voltage” condition. Inspect condition of electrical system, including loose battery
cables, both positive and negative. If battery disconnects from system, it could cause “high voltage” condition in electrical
system, causing OVCO circuit to trip.
If you have reset alternator once, and electrical system returns to normal charge voltage condition, there may have been
a one time, high voltage spike, causing OVCO circuit to trip.
If OVCO circuit repeats cutout a second time in short succession and shuts off alternator field circuit, try third restart.
If OVCO circuit repeats cutout, check that pin F in alternator-to-regulator harness is not shorted to B+ terminal on
alternator and that pin A in alternator-to-regulator harness is not shorted to B–. If it is shorted, alternator is defective.
If not, regulator is defective.
Page 6
TG31K
Section C: On-Vehicle Troubleshooting (CONT’D)
No Alternator Output – Test Charging Circuit
• TEST MEASUREMENTS ARE TAKEN ON HARNESS PLUG AT ALTERNATOR. TEST MEASUREMENT AT AN
EXTENDED HARNESS PLUG MAY AFFECT RESULTS.
• REMOTE-MOUNTED REGULATORS: CHECK CONDITION OF FUSES IN WIRING HARNESS BEFORE TROUBLE-
SHOOTING.
• BEFORE STARTING DIAGNOSTIC SEQUENCE, VERIFY THE FOLLOWING AND REPAIR/REPLACE IF NOT
TO SPEC:
—BATTERIES FOR STATE-OF-CHARGE (24.5-25.5 V), CONDITION, AND SECURE CONNECTIONS
—MASTER BATTERY SWITCH FOR FUNCTION
MASTER BATTERY SWITCH ON, KEY ON, ENGINE ON: Test for battery voltage at B+ terminal on alternator
to ground, then at IGN terminal on regulator to ground (A2-341 regulator: See page 2 for more information).
Does battery voltage exist at both locations?
Yes
ENGINE OFF: Disconnect 6-pin alternator-toregulator harness plug at regulator and connect
CEN A10-114 inline test tool to harness plug end
only. Make sure connections are secure.
Repair vehicle wiring as necessary. Run engine
and re-test charging circuit. Is charging system
performing properly?
No
No
Yes
System is operative.
MASTER BATTERY SWITCH ON, KEY OFF, ENGINE OFF: Readings of all five tests must pass.
1. Battery voltage test: Connect DMM red lead to socket D in test tool. Connect DMM black lead to socket C in test
tool. Battery voltage should exist.
2. Field coil resistance test: Set DMM to ohms test. Field resistance between sockets F and A in test tool should
measure nominal 1.0-1.5 ± 0.2 ohms. Field coil is defective if reading is less than 0.5 ohms or greater than 3 ohms.
3. Significant magnetism test:
a. Securely connect one jumper wire between socket F in test tool and B+ terminal on alternator.
b. Insert one end of second jumper wire in socket A in test tool. Momentarily (1 sec.) touch other end of second
jumper wire to alternator B– terminal. Spark will occur at B– terminal. Touch steel tool to shaft to detect
significant magnetism.
c. Remove both jumper wires.
4. Turn off master battery switch. Disconnect B+ battery cable on alternator. Check date code on DE housing.
• If date code is before September 8, 2010: Set DMM to diode test. Connect black lead on DMM to socket E in
test tool and red lead to B+ terminal on alternator. DMM should read OL. Reverse leads. DMM should read OL
again. Reconnect B+ battery cable to alternator. Turn on master battery switch.
• If date code is on or after September 8, 2010: Set DMM to ohms test. Connect black lead on DMM to socket E
in test tool and red lead to B+ terminal on alternator. DMM should read 0 ohms. Reverse leads. DMM should
read 0 ohms again. Reconnect B+ battery cable to alternator. Turn on master battery switch.
5. Phase supply test: Set DMM to diode test. Connect DMM black lead to socket B in test tool. Connect red lead to
alternator B+ terminal. DMM should read blocking in this direction. Then reverse leads. DMM should read flow
in this direction. Repeat for socket B and B– terminal. Tests should read flow in one direction and blocking in
the other direction.
Yes
Regulator is defective.
Alternator is defective.
No
SOCKET CONNECTIONS
Socket A F–
Socket B Phase
Socket C B –
Socket D B+
Socket E D+
Socket F F+
F
A
E
B
C
D
Figure 7 – CEN 6-pin A10-114 Inline Harness Tool
Socket Connections
If you have questions about your alternator or any of these inst ructions, or if you need to locate a Factory Authorized Service Dealer, please contact us at:
TG31K
TEL: 800.643.4633 USA and Canada • TEL: 847.866.6030 outside USA and Canada • FAX: 847.492.1242
C. E. Niehoff & Co.• 2021 Lee Street • Evanston, IL 60202 USA
E-mail us at service@CENiehoff.com
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