GMC 4000 Series Service Manual page 436

Figure 2 5 — Checking Regulator Circuits
FILTER CAPACITOR
(PART 8, Fig. 24)
If both ohmmeter readings are zero, the cap­
acitor is defective. Visually inspect for open sold­
ered connections and broken leads. To assem ble a
new capacitor properly, note location of the "+"
identifying mark in figure 23.
TRANSIENT SUPPRESSION DIODE
(PART 9, Fig. 24)
If the two ohmmeter readings are identical,
the diode is faulty.
BACK BIAS DIODE
(PART 10, Fig. 24)
Replace the diode if both readings are zero, if
both readings are infinite, or if both readings are
identical.
FIELD DISCHARGE DIODE
(PART 11, Fig. 24)
Replace the diode if both readings are zero,
if both readings are infinite, or if both readings
are identical.
EMITTER BASE RESISTOR (If Used)
(PART 12, Fig. 24)
Connect ohmmeter as shown. If the reading is
infinite, the resistor is open and must be replaced.
OUTPUT BASE RESISTOR
(PART 13, Fig. 25)
If one reading is infinite or nearly infinite, or
if both readings are infinite or nearly infinite, the
resistor is open.
G M C S E R V I C E M A N U A L
DRIVER TRANSISTOR
(PART 14, 14A, 14B, Fig. 25)
readings are very low and identical, the transistor
is shorted and must be replaced. Similarly, if both
readings in Step 14A or 14B are zero or very low
and identical, the transistor is shorted.
or if both readings are very high and identical, the
transistor is open and must be replaced.
A/C GENERATING SYSTEM
f I
Figure 2 6 — Checking Transistors for Shorts
If both readings in Step 14 are zero or if both
If both readings in Step 14 or 14B are infinite,
Sec. 6Y
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