longer conducts because the voltage has now decreased
The magnetism created in the core of the indicator
below its PRV. DR2, not conducting, turns TR2 off.
light relay, because of the battery voltage, is insufficient
This allows TR1 to operate, returning current to the
to overcome the spring tension and open the normally
field circuit. The cycle repeats itself as many times as
closed contacts. The contacts open when the alternator
necessary to maintain the preset output.
voltage increases to a value greater than battery voltage.
At this time the alternator is charging the battery, and
MAINTENANCE AND REPAIR
the indicator light is turned off by opening the contacts.
The fully transistorized regulator performs one
Do not adopt a hit-or-miss approach to trouble-
function only--to control the rotor current, limiting the
shooting, maintenance, and repair of electrical systems.
alternator voltage to a preset value. The course voltage
Hit-or-miss troubleshooting results in a great waste of
setting may be adjusted externally by relocating a screw
time and may result in serious damage to one or more of
in the base of the regulator. The screw contacts the
the components of the electrical system. Wrong adjust-
series of resistors, marked R7 through R10 in figure
ments by maintenance personnel have ruined many
6-39, and makes a connection to ground at the point
regulators, alternators, and batteries. The technician
of contact. Internal fine voltage adjustment is ac-
can easily determine if a wire is "hot," but to know the
complished by turning a slotted head screw on the
voltage and the amount of current flowing in the wire
potentiometer R5.
requires the use of instruments. A few quick checks
The operation of the fully transistorized regulator is
help you quickly identify and isolate electrical problems.
similar to the semitransistorized two-unit regulator.
TR1 and TR2 are PNP transistors. TR1 conducts the
A good visual inspection should be made of the
full battery voltage to the rotor windings to produce the
charging circuit before actual testing begins. Inspect
rotating magnetic field. TR2 controls the operation of
the battery case for cracks and leaks. Make sure the
TR1 by sensing the output voltage of the alternator.
battery posts, clamps, or cables are not broken and that
the connections are not corroded or loose. Also check
Internally, resistors R4 through R10 are connected
for insulation chaffing that could expose bare wire. The
in series, constituting a voltage divider circuit. R5 is a
top of the battery should be clean and dry. Dirt and
variable resistor. The voltage at the R5 tap is impressed
electrolyte on top of the battery cause excessive
upon the base of TR2. TR2 is operating in a
self-discharge. Be sure that the battery carrier is solidly
forward-bias condition (turned on). The base voltage is
mounted, in good condition, and properly secured. A
negative in relation to the emitter voltage. While TR2 is
loose battery carrier or battery hold-down will allow the
operating in the forward-bias condition, voltage flows
battery to be damaged by vibration and jarring. An
through the emitter-collector to provide the base
excessively tightened battery hold-down may buckle or
voltage for TR1. With TR1 forward-biased, the battery
crack the battery case.
voltage is provided to the rotor field. Diode D3 prevents
the battery voltage from grounding inside the regulator.
Raised cell covers or a warped battery case may
indicate that the battery has been overheated or
As the alternator voltage increases, it is sensed at
overcharged. This may be important when the results of
the voltage divider circuit. The higher potential at R5 is
the electrical tests are analyzed. Check the level of the
sensed by Zener diode D2. When the peak reverse
electrolyte in the battery. If, under normal conditions,
voltage (PRV) of the Zener is exceeded, D2 conducts,
distilled water has to be frequently added to the
placing a negative potential on the base of TR2. This
electrolyte, a high charging rate is indicated. These
will forward-bias (turn on) TR2. TR2 conducting,
conditions require that the charging rate be checked and
places the same potential on the base and emitter of
adjustments made if required. Likewise, if a battery has
TR1. This causes TR1 to stop conducting, opening the
to be replaced, the charging rate should be checked to
field circuit.
ensure the charging system is operating properly.
When the field circuit is opened, a reverse polarity
A variety of alternator regulators are used in
voltage is induced in the rotor winding as the magnetic
automotive vehicles, and test and adjustment pro-
field collapses. This voltage is conducted to ground
cedures may vary from type to type. The test
through D3 and back to the rotor, depleting its strength.
procedures presented here are general in nature, and
No damage occurs to the voltage regulator circuit. With
should not be substituted for the specific procedures
no rotor voltage, the alternator output is interrupted.
outlined in the applicable maintenance manuals.
The reduced voltage is sensed at Zener D2, which no
6-33
