C.E. Niehoff & Co. N1128 Troubleshooting Guides User Manual
Page 6
Page 6
TG0027A
Section 4: Advanced Troubleshooting
(CONT’D)
Shut off engine. With key off, engine off: Test for battery voltage at alternator 28 V B+
terminal. Does battery voltage exist?
Yes
No
Check and repair wiring and battery cables as necessary.
Continue test.
Chart 1 – 28 V LED Steady AMBER – No 28V Alternator Output – Test Charging Circuit
With DMM, check resistance across field coil. Connect red lead of DMM to socket A in alternator-to-regulator
harness plug. Connect black lead to B+ terminal on alternator. Does meter show 1.8 to 2.2 ohms?
Yes
No
T
T
T
T
T
T
T
T
T
T
Yes
Test phase signal into regulator (AC). Set meter to diode tester:
Connect red lead of DMM to socket C of regulator harness and black
lead to socket B. Meter should show voltage drop value.
Then reverse meter lead connections. Meter should show OL (blocking).
No
T
T
T
T
T
T
T
T
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T
Yes
No
T
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T
T
T
Regulator responded to overvoltage condition. Go to Chart 4
on page 8 to troubleshoot OVCO.
Figure 3 – Alternator-to-Regulator
4-Socket Harness Plug
SOCKET CONNECTIONS
A
F–
B
Phase Signal AC
C
B–
D
28 V B+
With key on, engine running: Test for battery voltage between IGN terminal on regulator and alternator
B– terminal. Does 28 V battery voltage exist?
Yes
No
T
T
T
T
T
With key off, engine off: Remove alternator-to-regulator 4-pin harness from regulator. Test for battery
voltage across sockets D and C in harness plug. Does 28 V battery voltage exist?
Alternator is defective.
T
T
T
T
T
Alternator is defective.
T
T
T
T
T
Alternator is defective.
T
T
T
T
T
Regulator is defective.
Yes
Connect jumper wire from socket A in regulator harness plug to B– terminal on alternator.
Spark will occur. Touch steel tool to shaft to detect significant magnetism. Is shaft magnetized?
No
T
T
T
T
T
Repair vehicle ignition circuit wiring as necessary. Continue test.
Yes
No
T
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T
T
T
Start engine. Wait 20 seconds. Is 28 V LED steady GREEN on regulator?
T
T
T
T
T
T
T
T
T
T
T
T
T
T
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T