Oscilloscope Test Pattern

The oscilloscope, among other pieces of test equipment, may be used to check the condition of the alternator. When the alternator diodes and stator are functioning properly, the scope pattern appears as a series of small waves with the headlights and accessories turned off.

By positioning the scope controls, the pattern may be enlarged to show the wave forms as being regularly spaced and all of the same height with the headlights on high beam.

Breaks in the pattern indicate open diodes or stator or shorted diodes or stator. The defective alternator must be replaced.

Fig 1: Normal Pattern Headlights & Accessories Turned Off

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Fig 2: Normal Pattern Headlights On High Beam

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Fig 3: Abnormal Pattern

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Fig 4: Harness Jumper Connection (Typical)

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Fig 5: Harness Jumper Connection (Chrysler Corp.)

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Fig 6: Delco-Remy Alternator (1968)

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