-25-
STATIC MEASUREMENTS
With the power OFF, connect the negative lead of your
VOM to any ground and the positive lead to the emitter
of Q3 as shown in Figure 24. Set the VOM to read 9
volts DC and turn ON the power. The voltage at the
emitter of Q3 should be approximately 1 volt. If your
reading is different by more than 0.5 volts, turn off the
power and check your battery of power supply voltage.
Also check components R7, R9, R10 and Q3.
Q3 BIAS
If you do not have an RF generator or oscilloscope, skip the following test and go to Section 4.
DYNAMIC MEASUREMENTS
With the power turned OFF, connect the oscilloscope and
the RF generator to the circuit as shown in Figure 25. Set
the RF generator at a frequency of 455kHz, no
modulation and minimum amplitude output. Set the
oscilloscope vertical sensitivity at 1 volt/division. The
scope probe must have an input capacitance of less
than 50pF or it will detune transformer T3. Turn the
power ON and slowly increase the amplitude of the RF
signal until you have 4 volts peak to peak on the
oscilloscope. Tune transformer T3 for a maximum output
while readjusting the RF generator amplitude to keep
4Vpp at the oscilloscope. After T3 is aligned, move the
scope probe tip to the base of Q3 and record the peak
to peak amplitude of the signal here:
Vb=__________Vpp.
Turn the power OFF. The AC gain of the second IF
amplifier at 455kHz is equal to 4/Vb, and should be
greater than 100. If your gain is less than 100, check
components C7, C8, R7, R9 and R10. Also, make sure
that transistor Q3 is properly installed.
AC GAIN
Figure 24
GND
TP10
Figure 25
GND
TP10
Output Adjust
Generator
GND
TP10
Oscilloscope
.02
m
F
Probe
AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 26
