CAP
ROTOR
C A PA C I TO R
SEAL
A S S E M B LY
WEIGHT
SPRING
CAM
A D VA N C E
WEIGHT
TERMINAL
C O N TA C T
SUPPORT
BREAKER
GREASE
WEIGHT BASE AND
ARM
CUP
S H A F T A S S E M B LY
BRONZE BUSHING
ASf06043
COUPLING
Figure 6-43.--Side and top view of a distributor.
a contact-controlled system, conventional breaker
a spring-loaded diaphragm connected by a linkage to
points turn the transistor emitter-base circuit ON and
the distributor and by a vacuum passage to the
OFF at the proper time in relation to the engine timing.
carburetor. The opening to the carburetor is on the
Because of the low voltage controlled by the breaker
atmospheric side of the throttle when the throttle is in
points (one-half to three-fourths of an ampere), their
the idling position. There is no advance in this position
life is greatly increased over that of the conventional
because the opening is under atmospheric pressure. As
ignition system.
the throttle opens, it swings past the opening of the
vacuum passage, exposing the advance mechanism
There are several advantages offered by the
diaphragm to intake manifold vacuum. The diaphragm
transistorized ignition system. These are extended
operates the advance-mechanism linkage. It rotates the
breaker point life, extended periods between engine
breaker plate and breaker points in the direction of
tuneups, extended spark plug life, and higher available
distributor rotation. This causes the breaker points to
voltage at the spark plugs.
open earlier, which advances the time that the spark
There are two basic types of transistorized ignition
occurs in the cylinder.
systems. They are the contact-controlled systems and
the transistor-controlled magnetic pulse system. The
Transistor Ignition Systems
basic difference between the two is the manner in which
The transistor ignition system is designed to
the emitter-base circuit within the transistor is
overcome some of the drawbacks of the conventional
controlled. This control can be exercised by either
ignition system. The output of the conventional ignition
mechanical or electronic means.
system is limited to the amount of current in the
NOTE: Transistors are discussed in NEETS,
primary circuit. Approximately 5 amperes of current
Module 7. You should review this module for a better
can be carried in the primary circuit to maintain a
understanding of transistors.
reasonable breaker point life. Any increase in current
shortens the breaker point life.
CONTACT-CONTROLLED SYSTEM.--In the
conventional battery system, when the ignition switch
The transistor can switch large amounts of current
is closed, current flows through the ignition coil
through the action of a very small control current. The
primary winding and the breaker points. The breaker
switching action involves no moving parts and is
points carry the full primary current. Since the amount
instantaneous when the circuit is designed properly. In
6-39
