Usage:
Troubleshooting
To reduce troubleshooting difficulty, find the problem in the Problem List that best describes the fault that is occurring. To make a repair to a problem, make reference to the probable cause.
This list of problems and probable causes give an indication of where the possible problem is and what repairs are needed. Sometimes more or other repair work is needed beyond the recommendations in the list. Remember that a problem is not normally caused by one part, but by the relation of one part with other parts. This list does not give all possible problems and probable causes. The serviceman must find the problem and its source, then make the necessary repairs.
Problem List
- 1. Alternator does not charge.
- 2. Alternator charge rate is low or not regular.
- 3. Alternator charges too much.
- 4. Alternator is noisy.
- 2. Alternator charge rate is low or not regular.
Problems
Problem 1: Alternator Does Not Charge
Probable Cause:
1. Loose drive belt for alternator:
Adjust the alternator drive belt.
2. Loose alternator drive pulley:
Check the pulley for wear. If it is worn, install a new pulley. Tighten the pulley nut to a torque of 100 ± 7 N·m (75 ± 5 lb ft).
3. Charging or ground return circuit or battery connections are defective:
Inspect all cables and connections. Clean and tighten all connections. Replace defective parts.
4. Field coil or regulator is defective:
Install a new field coil or regulator.
Problem 2: Alternator Charge Rate Is Low Or Not Regular
Probable Cause:
1. Loose drive belt for alternator:
Adjust the alternator drive belt.
2. Loose alternator drive pulley:
Check the pulley for wear. If it is worn, install a new pulley. Tighten the pulley nut to a torque of 100 ± 7 N·m (75 ± 5 lb ft).
3. Charging or ground return circuit or battery connections are defective:
Inspect all cables and connections. Clean and tighten all connections. Replace defective parts.
4. Regulator is defective:
Replace the regulator.
5. Rectifier is defective:
Replace the rectifier.
Problem 3: Alternator Charges Too Much
Probable Cause:
1. Alternator or regulator has loose connections:
Tighten all connections to alternator or regulator.
2. Regulator is defective:
Install a new drive belt for the alternator.
Problem 4: Alternator Is Noisy
Probable Cause:
1. Drive belt for alternator is worn or defective:
Install a new drive belt for the alternator.
2. Loose alternator drive pulley:
Check the pulley for wear. If it is worn, install a new pulley. Tighten the pulley nut to a torque of 100 ± 7 N·m (75 ± 5 lb ft)
3. Drive belt and drive pulley for alternator are not in alignment:
Make an adjustment to put the drive belt and drive pulley in correct alignment.
4. Alternator bearings are worn:
Install new bearings in the alternator.
Alternator Output Test
NOTE: These procedures are for testing the alternator while on the machine. However, the listed output specifications apply to On Machine testing or Bench testing.
1. Put the multimeter positive (+) lead on the POS terminal of the alternator. Put the negative (-) lead on the GRD terminal or the frame of the alternator. Put the clamp-on ammeter around the positive output wire of the alternator.
2. Turn off all electrical accessories. With the fuel off, crank the engine for 30 seconds. Wait two minutes to let the starting motor cool. If the system appears to operate at the specifications, crank the engine again for 30 seconds.
NOTE: Cranking the engine for 30 seconds partially discharges the battery in order to do a charging test. If the battery is already low in charge, skip this step. Jump-start engine or charge as required.
3. Start the engine and run at full throttle.
NOTE: Full throttle approximates the required drive pulley speed of 5000 rpm.
4. Immediately check output current. When operating correctly, this initial charging current is equal to or greater than the full output current shown below:
3T6352 ... 35A
5N5692 ... 45A
7G7889 ... 60A
5. The alternator output voltage should stabilize within approximately 10 minutes at full throttle (possibly longer depending upon battery size, condition and alternator rating). When operating correctly, the alternator output voltage is:
3T6352 ... 27.4 ± 0.6 V
5N5692 ... 27.4 ± 0.6 V
7G7889 ... 14.0 ± 0.3 V
If the alternator is NOT performing within the specifications, see the Fault Conditions And Possible Causes chart.
6. The charging current during this period should taper off to less than approximately 10 amps, depending again upon battery and alternator capacities. If the charging current does not decrease as specified, see the Fault Conditions And Possible Causes chart.
Alternator Component Tests
Regulator Test
Test Circuit For Regulator Test
This test is performed to determine an alternator or regulator malfunction. This test does not cover all of the failure possibilities, but verifies a few common problems. See the Test Equipment chart for the equipment needed for this test.
Alternator output voltage is regulated by controlling field coil current. The regulator senses output voltage. If the voltage is low, the regulator allows field current flow and the voltage builds. When output voltage exceeds the upper limit, field current is turned off. The output voltage of a properly functioning alternator and regulator is:
3T6352 ... 27.4 ± 0.6V
5N5692 ... 27.4 ± 0.6V
7G7889 ... 14.0 ± 0.3V
The voltage should not vary more than approximately 0.3V during this process. This test measures voltage when the regulator turns field current on and off and determines if there is an open or short in the diode trio, field coil or regulator.
1. Connect variable power source (VPS) positive (+) lead to the alternator POS and R terminals as shown. Connect VPS negative (- ) lead to the alternator GRD terminal or frame ground.
2. Adjust the voltage of the VPS until ammeter (A) first indicates current draw. Measure voltage (V) and write this measurement down as turn-on voltage. When correctly operating, the turn-on voltage is:
3T6352 ... 27.4 ± 0.6V
5N5692 ... 27.4 ± 0.6V
7G7889 ... 14.0 ± 0.3V
The regulator is bad if the turn-on voltage is not as specified.
3. Ammeter (A) reads field current. When correctly operating, the field current is:
3T6352 ... 3.3 to 3.8A at 24V
5N5692 ... 2.5 to 2.8A at 24V
7G7889 ... 5.7 to 7.1A at 12V
NOTE: Divide the voltage from Step 2 by the resistance of the field coil winding (as shown in specifications). This also gives the field current as seen on ammeter (A) for a correctly operating system.
If ammeter (A) indication is zero amps, the rectifier, field coil or regulator are open. If ammeter (A) indication is too high, it is possible the field coil is shorted.
4. If the measurements in Steps 2 and 3 are correct, go to Step 5. If they are NOT correct, the alternator and/or regulator are bad.
5. Adjust VPS to the turn-on voltage as measured in Step 2. Slowly increase the voltage until ammeter (A) indicates zero amps. Write this voltage down as turn-off voltage.
6. When correctly operating, the difference between the turn-off and turn-on voltages is no more than 0.3V. A larger value indicates a regulator malfunction. Also, ammeter (A) should drop sharply to zero amps. If not, the regulator is faulty.
7. If the alternator and regulator meet all test requirements and there is still a problem, do the additional component tests that follow.
Capacitor Test
Capacitor
(1) Housing. (2) Ring terminal.
1. Remove the capacitor from the alternator.
2. Place and hold ring terminal (2) on housing (1). This discharges the capacitor.
NOTE: Each time this test is done, discharge the capacitor.
3. Put the multimeter on the 20M resistance (Ohms) scale. Connect a multimeter lead to ring terminal (2). Connect the other multimeter lead to housing (1).
4. When correctly operating, the resistance is very low for a short period of time and then it should stabilize above 100 000 ohms (meter reading 0.10 or greater).
5. If the reading is not correct, replace the capacitor.
Field Coil Tests
Field Coil
(1) Leads. (2) Housing.
Field Coil Continuity Test
1. Put the multimeter on the 200 ohm resistance (Ohms) scale. Touch and hold a meter lead on each lead (1).
2. For correct operation, the resistance value is:
3T6352 ... 6.3 to 7.3Ohms
5N5692 ... 8.5 to 9.5Ohms
7G7889 ... 1.7 to 2.1Ohms
3. If the resistance is not correct, the field coil is open or shorted. Replace the field coil.
Field Coil Ground Test
1. Put the multimeter on the 20M resistance (Ohms) scale. Touch and hold one meter lead to one coil lead (1). Touch and hold the other meter lead to housing (2).
2. For correct operation, the resistance is 100 000 ohms or greater (meter reading 0.10 or greater).
3. If the meter reading is LOW, the field coil is grounded. Replace the field coil.
Stator Tests
Stator
(1) Leads. (2) Frame.
Stator Winding Continuity Test
1. Connect the meter leads between each pair of stator leads (1) for a total of three readings.
2. For correct operation, all three readings are approximately the same.
3. If any two readings differ by 0.10 ohms or more, replace the stator.
Stator Winding Ground Test
1. Put the multimeter on the 20M resistance (Ohms) scale. Check each stator lead (1) for a short to ground. Connect one meter lead to a stator lead (1) and touch the other meter lead to stator frame (2). Repeat for each stator lead (1).
2. For correct operation, the resistance is 100 000 ohms or greater (meter reading 0.10 or greater) for each stator lead.
3. If the meter reading is low, the stator is grounded. Replace the stator.
Diode Trio Test
Diode Trio
(1) Single terminal. (2) Terminals.
1. Put the multimeter on the diode scale. Connect the meter to single terminal (1) and one of terminals (2). Note the meter reading.
2. Reverse the meter leads and note the meter reading.
3. When correctly operating, the reading for one Step is OL and the reading for the other Step is .4 to .9 volts.
If the readings are not correct the diode trio is open or shorted. Replace the diode trio
4. Repeat Steps 1-3 for the other two terminals (2).
Rectifier Tests
Rectifier
(1) Negative (-) diode clips. (2) Grounded heat sink. (3) Positive (+) diode clips. (4) Insulated heatsink.
For the following tests all diode clips (1) and (3) must not contact any thing. Bend all diode clips (1) and (3) away from the studs.
NOTE: To check the diodes, it is not necessary to disassemble the alternator as far as shown.
Positive Diode Check
1. Put the multimeter on the diode scale. Connect the meter leads to insulated heat sink (4) and one of positive (+) diode clips (3). Note the meter reading.
2. Reverse the meter leads and note the meter reading.
3. When correctly operating, the reading for one Step is OL and the reading for the other Step is .4 to .9 volts.
If both readings are OL or low (0 to .1 volts), the diode is open or shorted. Replace the rectifier.
4. Repeat Steps 1-3 for the other two positive (+) diode clips (3).
Negative Diode Check
1. Put the multimeter on the diode scale. Connect the meter leads to grounded heat sink (2) and one of negative (-) diode clips (1). Note the meter reading.
2. Reverse the meter leads and note the meter reading.
3. When correctly operating, the reading for one Step is OL and the reading for the other Step is .4 to .9 volts.
If both readings are OL or low (0 to .1 volts), the diode is open or shorted. Replace the rectifier.
4. Repeat Steps 1-3 for the other two negative (-) diode clips (1).
Insulated Screw Check
Rear Frame
(1) Screw. (2) Screw. (3) Screw.
It is possible for damaged or missing insulators to cause improper battery charging and damage electrical components. Carefully inspect the component mounting screws.
Screws (1) and (2) which fasten the field coil leads to the regulator, have insulators on them. Screw (3) which fastens the POS strap and the capacitor lead to the rectifier, has an insulator.
The insulators electrically isolate the screws from the attaching components. Screws (1), (2) and (3) should have NO continuity with the attaching components.
Restoring Residual Magnetism
It is possible for charging problems to occur when installing new or rebuilt alternators that have lost their residual magnetism. These alternators have residual magnetism in the rotor core to generate sufficient current to start the charging process. Some of the probable causes of reduced residual magnetism are:
- * Dropping or rough handling of the alternator.* Storage temperatures above approximately 38°C (100°F).* Extended storage periods of more than three to six months.* Manufacturing tolerances in the alternator.* Alternator disassembled for repairs and testing.
When the residual magnetic field is reduced below the level to "excite" the alternator, perform the following procedure to restore it again.
Procedure
Connections For Restoring Residual Magnetism
(1) Jumper wire.
Do the procedure that follows to restore the residual magnetism in the alternators.
1. Connect a 24V battery between the BAT and GRD terminals of the alternator (as shown).
2. For approximately two seconds, connect jumper wire (1) between the BAT and the R terminal. When correctly operating, a spark occurs as jumper wire (1) touches the R terminal. If there is not a spark, the alternator has an internal open.
3. This restores the residual magnetism in the rotor coil.