Chevrolet 30 Series 1967 Service Manual page 379

CHECKING CHECKING CHECKING
DIODE D1 RESISTOR R3 RESISTOR R4
CHECKING
RESISTOR R1
F ig . 2 5 i—Pulse A m p lifie r Component Checks
IGNITION PULSE AMPLIFIER
DISASSEMBLY
To check the amplifier for defective components, pro­
ceed as follows:
1. Remove the bottom plate from the amplifier.
2. To aid in reassembly, note the locations of the lead
connections to the panel board.
3. Remove the three panel board attaching screw, and
lift the assembly from the housing.
4. To aid in reassembly, note any identifying markings
on the two transistors and their respective locations
on the panel board and heat sink assembly.
5. Note the insulators between the transistors and the
heat sink, and the insulators separating the heat sink
from the panel board.
. Remove the transistor attaching screws, and sepa­
6
rate the two transistors and heat sink from the panel
board.
7. Carefully examine the panel board for evidence of
damage.
COMPONENT CHECKS (Figs. 24i and 25i)
With the two transistors separated from the assembly,
an ohmmeter may be used to check the transistors and
components on the panel board for defects. An ohmmeter
having a - volt cell, which is the type usually found
1 1 / 2
in service stations, is recommended. The low range
scale on the ohmmeter should be used except where
specified otherwise.
A 25 watt soldering gun is recommended, and a 60%
tin 40% lead solder should be used when re-soldering.
Avoid excessive heat which may damage the panel board.
Chip away any epoxy involved, and apply new epoxy which
is commercially available.
CHECKING CHECKING
RESISTOR R5 RESISTOR R2
CHECKING
CAPACITOR Cl
Fig . 26i—Pulse A m p lifie r Internal C ircu itry
In order to check the panel board assembly, it is nec­
essary to unsolder at the locations indicated in Figure 5i
the two capacitors C2 and C3. In all of the following
checks, connect the ohmmeter as shown and then reverse
the ohmmeter leads to obtain two readings. Internal
circuitry of the amplifier is shown in Figure 26i.
1. Transistors T R l and TR2: Check each transistor by
referring to Figure 27i. If both readings in Step 1 are
zero, the transistor is shorted. If both readings in
Step 2 are zero, the transistor is shorted; and if both
readings are infinite, the transistor is open. Inter­
pret Step 3 the same as Step 3.
2. Trigger Transistor TR3: If both readings in Step 1
are zero, the transistor is shorted. If both readings
in Step 2 are zero, the transistor is shorted; and if
both readings are infinite, the transistor is open.
Interpret Step 3 the same as Step 2.
3. Diode Dl: If both readings are zero, the diode is
shorted; and if both readings are infinite, the diode is
open.
4. Capacitor Cl: If both readings are zero, the capaci­
tor is shorted.
5. Capacitors C2 and C3: Connect the ohmmeter across
each capacitor (not illustrated). The capacitor is
shorted if both readings are zero.
. Resistor R l: The resistor is open if both readings
6
are infinite.
7. Resistor R2: Use an ohmmeter scale on which the
1800 ohm value is within, or nearly within, the mid­
dle third of the scale. If both readings are infinite,
the resistor is open.
. Resistor R3: Use an ohmmeter scale on which the
8
680 ohm value is within, or nearly within, the middle
third of the scale. If both readings are infinite, the
resistor is open.
9. Resistor R4: Select an ohmmeter scale on which the
ENGINE-ELECTRICAL 6Y-31
CHEVROLET TRUCK SERVICE MANUAL