WAVEFORM CHECK USING AN OSCILLOSCOPE


MEASUREMENT METHOD



Connect the oscilloscope special patterns pick-up to the alternator "B" terminal.

STANDARD WAVEFORM
Function
 Special pattern
Pattern height
 Variable
Variable knob
 Adjust while viewing the waveform.
Pattern selector
 Raster
Engine speed
 Curb idle speed



note The voltage waveform of the alternator "B" terminal can undulate as shown in the illustration. This waveform is produced when the regulator operates according to fluctuations in the alternator load (current), and is normal for the alternator. In addition, when the voltage waveform reaches an excessively high value (approximately 2 V or higher at idle), it often indicates an open circuit due to a brown fuse between alternator "B" terminal and battery, but not a defective alternator.

EXAMPLE OF ABNORMAL WAVEFORMS


note
  1. The size of the waveform patterns differs largely, depending on the adjustment of the variable knob on the oscilloscope.
  2. Identification of abnormal waveforms is easier when there is a large output current (regulator is not operating). (Waveforms can be observed when the headlamps are illuminated.)
  3. Check the conditions of the charging warning lamp (illuminated/not illuminated). Also, check the charging system totally.

<4A9-Vehicles for Russia>
Abnormal waveform
 Problem cause
Example 1

Open diode
Example 2

Short in diode
Example 3

Broken wire in stator coil
Example 4

Short in stator coil

<4B1>
Abnormal waveform
 Problem cause
Example 1

Open diode
Example 2

Short in diode
Example 3

Broken wire in stator coil
Example 4

Short in stator coil

<4N1, 4A9-Except vehicles for Russia>
Abnormal waveform
 Problem cause
Example 1

Open diode
Example 2

Short in diode
Example 3

Broken wire in stator coil
Example 4

Short in stator coil