Am Detector And Agc Test; System Check - Elenco Electronics AM/FM-108K Assembly And Instruction Manual

DYNAMIC MEASUREMENTS

AM DETECTOR AND AGC TEST

Connect your VOM and RF generator as shown in Figure 14.
V
COM V
TP15
Set the VOM to accurately read 2 volts DC and set
the output of the RF generator for 455kHz, no
modulation, and minimum voltage output. Turn the
power ON and slowly increase the amplitude of the

SYSTEM CHECK

Connect your equipment as shown in Figure 15.
.001µF
GENERATOR
Hz
TP15
Set the RF generator at 455kHz, 1kHz at 80%
modulation and minimum voltage output. Turn the
power ON and set the volume control at maximum.
Slowly adjust the amplitude of the RF generator
If your RF generator does not have amplitude modulation and
you do not have an oscilloscope, skip to Section 3.
.001µF
Figure 14
generator until the voltage at TP5 just starts to drop.
This point is called the AGC threshold with no IF
gain. Make a note of the amplitude setting on the RF
generator here: ____________.
Figure 15
output until you hear the 1kHz tone on the speaker.
If this test fails, turn the power OFF and check R42
and D4. Turn the power OFF.
-16-
GENERATOR
Hz
TP15
TP15