Diodes can be checked with the alternator on the vehicle using a scope. Scope testing can identify open or shorted diodes, as well as problems in the stator coils.
The scope patterns shown below include:
a) Normal alternator output;
b) one diode short-circuited;
c) two diodes of the same polarity short-circuited;
d) one diode open;
e) two diodes open;
f) one phase of the stator coil short-circuited;
g) one phase of the stator coil disconnected; and, h) two phases of the stator coil short-circuited.
This brief self-test will help you measure your understanding of The Charging System. The style is the same as that used for A.S.E. certification tests. Each incomplete statement or question is followed by four suggested completions or answers. In each case, select the one that best completes the sentence or answers the question.
1. A regulator controls alternator output voltage by regulating:
A. sine-wave voltage
C. field current
D. output current
2. In an alternator, alternating current is converted to direct current by the:
3. If the charging system indicator lamp goes on with the engine running, the cause may be loss of voltage at terminal:
6. When performing a visual inspection of the charging system, the alternator drive belt should be checked for proper tension.
Technician "A" says that new-belt tension specs are higher than those for used belts.
Technician "B" says that the belt tension is different for different Toyota models.
Who is right?
D. Neither A nor B
7. The amount of current the alternator must supply or ignition and accessories is about:
A. four amps
B. six amps
C. eight amps
D. ten amps
8. In an alternator output test under load, the output should be:
D. "F D. within 20% of rated output
4. With the engine not running and the ignition ON, the charge lamp should light. If it doesn't, this may indicate a:
A. burned out bulb
B. grounded bulb
C. loose drive belt
D. overcharged battery
5. Which alternator terminal can be grounded for test purposes?
9. To check for excessive voltage drop on the insulated side of the alternator's output circuit, you would connect a voltmeter between the:
A. battery terminal and ignition switch
B. battery terminal and ground
C. battery terminal and alternator "S" terminal
D. battery terminal and alternator "B" terminal
10. High resistance in an alternator output circuit is often caused by:
a shorted diode
loose or corroded connections
a bad regulator
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