System Check - Elenco Electronics AM/FM-108CK Assembly And Instruction Manual

DYNAMIC MEASUREMENTS
AM DETECTOR AND AGC TEST
Connect your VOM and RF generator as shown in Figure 14.
V
Amps COM V/Ω
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 generator until the

SYSTEM CHECK

Connect your equipment as shown in Figure 15.
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 output until you
If your RF generator does not have amplitude modulation and
you do not have an oscilloscope, skip to Section 3.
.001μF
Figure 14
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
hear the 1kHz tone on the speaker. If this test fails, turn
the power OFF and check R42, D4 and TP5. Turn the
power OFF.
-17-
Generator
Hz
.001μF
TP15
Oscilloscope
TP15