C.E. Niehoff & Co. C840D Troubleshooting Guides

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

C840D Alternator

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

Section B: Schematic Diagram .................................... 3

Section C: On-Vehicle Troubleshooting ..................... 4-5

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.

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Page 1

Section A: Description/Operation

CEN C840D Alternator/Regulator Description and Operation

C840D 28 V, 525 A alternator is internally rectified. All windings and current-transmitting components are non-moving,
so there are no brushes or slip rings to wear out. C840D alternator is furnished with an open duct in the anti-drive end
cover plate, which accommodates a 4” duct.

This alternator is externally energized when the battery master switch on the vehicle is turned on and provides power
to the regulator through the IGN circuit (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 anti-drive end rectifier housing and supplied to the battery from the alternator B+ termi­nal. See Figure 4 on page 3. Alternator output current is self-limiting and will not exceed rated capacity of alternator.
Regulator maintains alternator output voltage at pre-determined regulated setting (see below for setpoints) as vehicle
electrical loads are switched on and off.

A2-346 regulator furnished with some units includes:

• Optional external IGN terminal for energize connection. This regulator can function with or without vehicle ignition.
When necessary, IGN terminal on regulator is connected to vehicle ignition 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 4.

• Tricolored LED. See page 4.

• Battery type selection and battery maintenance/function are the sole responsibilities of the customer.

• J1939 connector to be used with optional A9-4036 harness.
— When A9-4036 temperature/voltage sense 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 1.
— When A9-4036 temperature/voltage sense harness is connected, regulator will automatically optimize the charge
voltage for battery type based on temperature. Also, vehicle manufacturer-requested functions of 1939 interface are
available through connector. See Column 3 in Table 1.

Table 1 — A2-346 Regulator Voltage/Battery Switch Position

Switch Position

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

A9-4036 Harness Not Connected

(Voltage Select)

A9-4036 Harness Connected

(Battery Select)

DO NOT US E POSITION # 4

Figure 2—Voltage/Battery Switch

Page 2

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B+ Terminal

Section B: Schematic Diagram

P Terminal

B– Terminal

Open duct

D+ Terminal

Figure 3 — C840D Alternator and A2-346 Regulator Terminals

IGN Terminal

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F

PHASE RPM SIGNAL

D

BK

P

IGN

R

BR

CONNECTOR 1

CONNECTOR 2

W

G

Figure 4 — C840D Alternator Schematic Diagram

Page 3

Section C: On-Vehicle Troubleshooting

A2-346 Regulator Troubleshooting

Main diagnostic feature of these regulators is a tricol­ored LED opposite the alternator-regulator harness
receptacle. LED works like a voltmeter, measuring
charging voltage. See Table 2 for LED diagnostics.

These regulators have 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 flashing RED). OVCO circuit can also optionally
reset when system voltage normalizes after 2-minute
wait.

An additional A9-4036 harness may or may not be used
with the A2-346 regulator:

• When A9-4036 temperature/voltage sense harness is
not connected, regulator will operate in fixed voltage
setting determined by the select switch position on
the bottom of the regulator.

• When A9-4036 temperature/voltage sense harness is
connected, regulator will automatically optimize the
charge voltage for battery type selected based on
temperature. Also, vehicle manufacturer-requested
functions of 1939 interface are available through
connector.

General Troubleshooting

OVCO condition

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. If it is shorted, alternator is
defective. If not, regulator is defective.

No air-conditioning/ NO ALT OUTPUT light is on

Some older vehicles may experience a condition when
the air-conditioning may drop out during normal
vehicle operation. If that should occur, check for regula­tor setpoint voltage at D+ terminal and 12 V-18 V at P
terminal. If present, check vehicle wiring. If not present,
check for diode voltage drop between pin E on alterna­tor-to-regulator harness and alternator B+ terminal. If
not present, alternator is defective. If present, substitute
a known good regulator, run engine, and check for regu­lator setpoint voltage. If present, original regulator was
defective. If not present, go to troubleshooting chart on
page 5.

LED COLOR STATUS

GREEN Solid

AMBER Solid

RED Solid

Page 4

Flashing

Flashing

TABLE 2 – A2-346 Regulator LED Diagnostics

Alternator and regulator operating normally.

Low system volta ge — Electrical load exceeds
alternator rating at present rotor speed.

Alternator fault — No output.

High system voltage – May occur during
normal load switching.

OVCO tripped.

ACTION

No action required.

When loads decrease or speed increases, LED
should be solid GREEN. If not, check drive belt
and charging system connect ions.

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 condition in “General Troubleshooting”
section above.

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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. Does battery voltage exist at both locations?

Yes

Disconnect 6-pin alternator-to-regulator 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 four 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 C 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 end of a jumper wire to socket F in test tool.
b. Momentarily (1 sec.) touch other end of jumper wire to alternator B+ terminal. Spark will occur at B+ terminal.
Touch steel tool to shaft to detect significant magnetism.

4. Phase supply test: Set DMM to diode test. Connect DMM black lead to socket E 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 E and B– terminal. Tests should read flow in one direction and blocking in
the other direction.

Yes

No

Regulator is defective.

Alternator is defective.

SOCKET CONNECTIONS

Socket A Temp Sense
Socket B Not used
Socket C B –
Socket D B+
Socket E Phase
Socket F F+

F

A

E

B

C

D

Figure 5 – CEN 6-pin A10-114 Inline Harness Tool

Socket Connections

If you have questions about your a lternator or a ny of these instructions, or if you need to locate a Factory Authorized Service Dealer, please contact us at:

C. E. Niehoff & Co.• 2021 Lee Street • Evanston, IL 60202 USA

TEL: [phone] USA and Canada • TEL: [phone] outside USA and Ca nada • FAX: [phone]

TG77A

E-mail us at [e-mail]

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