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Alternator Testing

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Practically all the alternator and charge system faults can be diagnosed with an oscilloscope.

The oscilloscope must be connected to terminal D+ and earth. All loads with the exception of the ignition system should be switched off. During measurement the engine should be running at least 3000 rpm.

When using an oscilloscope without a dc voltage amplifier, the curves will appear on the zero line.

Normal Operation (3K) Normal Operation (oscilloscope without dc amplifier)
Normal Operation (3K) Normal Operation (oscilloscope with dc amplifier)
+ve diode fault (3K) Short circuit of positive diode
-ve diode fault (3K) Short circuit of negative diode
+ve diode fault (3K) Interruption of positive diode
-ve diode fault (3K) Interruption of negative diode
excitation diode fault (3K) Short circuit of excitation diode
excitation diode fault (3K) Interruption of excitation diode
stator fault (3K) Short circuit of stator winding
rotor fault (3K) Short circuit of rotor windings
stator fault (3K) Earth contact of stator winding
stator fault (3K) Interruption of stator winding
rotor fault (3K) Interruption of rotor winding

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