c. Stage Gain Measurements. Use the pro-
(2) If the gains of the stages are abnor-
mally low, use isolating techniques
cedures given below when audio amplifier
(para 2-9) to determine the defec-
3A1 is believed to be defective. Stage gain
tive part within the stage.
test points are indicated in figure 2-30. Parts
location are given in figures 2-26 and 2-27.
2-9. lsolating Troubles
(1) Connect. the equipment as shown in
When trouble has been localized to audio
figure 2-30. Use the ME-SOB/U
amplifier 3A1, use the techniques listed below
and measure between the test points,
to isolate the defective part:
listed in the chart below, and chassis
a. Take voltage measurements at the termi-
ground. Adjust the audio oscillator
nals of 3A1 as indicated in figure 2-29.
for 0.1-volt ac output at. 3 kc. Com-
b. If the voltage indications are normal,
pute the gain for each stage by divid-
take resistance measurements (fig. 2-29) to
ing the measured Output voltage by
isolate open or short circuits. Refer to the re-
the measured Input voltage. The
sistance and continuity chart (para 2-7c) and
gain should be as listed in the chart
c. Use the schematic diagrams (fig. 4-10
and 4-11) and the wiring diagrams (fig. 2-
Audio amplifier 3A1
31, 4-15, and 4-16) to trace circuits and fur-
Test points (fig. 2-30)
ther isolate the faulty part.
Take resistance readings only
with Multimeter ME-26B/U. The de source
in some multimeters can destroy the transis-
tors by causing excessive current through
Figure 2-30. Test unit audio amplifier 3A1, stage gain test setup diagram.