Q7 Bias; Am Oscillator Circuit - Elenco Electronics AM/FM-108K Assembly And Instruction Manual

STATIC MEASUREMENTS

Q7 BIAS

Connect your VOM to the circuit as shown in Figure 20.
Connect a clip lead from TP6 to the collector of Q7.
This short prevents Q7 from oscillating. Set the VOM
to read 2 volts DC and turn the power ON. The DC
voltage at TP7 should be about 1.6 volts. If the
voltage in your circuit differs by more than .5 volts,
If you do not have an oscilloscope, skip to the AM Final Alignments.
DYNAMIC MEASUREMENTS

AM OSCILLATOR CIRCUIT

Connect your test equipment to the circuit as shown in Figure 21.
Set the scope to read 1 volt per division and turn the
power ON. The scope should display a low voltage
sinewave. The frequency of the sinewave should
change when the tuning gang is turned. If your
Short TP6 to the
collector of Q7
as shown.
Figure 20
Figure 21
-25-
leave the power ON and check the battery voltage. If
the battery voltage is greater than 8.5 volts, check
components R31, R32, R33 and Q7.
Turn the power OFF.
circuit fails this test, check components Q7, gang
capacitor, C28, C29, C30, C31, L4 and L5. Turn the
power OFF.
V
COM V
TP15
TP15