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wj-8/18-iy/fE
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k l u l i v c k
MAINTENANCE
Connect the Signal Generator RF output to A4XA7
pin 57 using a short coaxial cable with clip leads on
one end.
Connect cable shield to the IF Motherboard
ground plane.
Terminate the generator with a 50 ohm
load.
Set the Generator output frequency to 455 kHz
and output level to -47 dBm.
Energize the receiver.
The Oscilloscope should display
a level of 90 mV.
6.
Move the RF Voltmeter clip lead to A4XA7 pin 13.
The
Oscilloscope should display a level of 20 mV.
7.
Turn on the Signal Generator AM Modulation and set it
for 50% modulation at 400 Hz.
8.
Connect the Oscilloscope vertical input to A4XA7 pin 51
using a coaxial
with clip leads on
one end.
The
Oscilloscope should display a level of 1.0 V p-p at 400
Hz superimposed on a dc level of + 3.8 Vdc.
8.
If the signal in steps 4 and 8 is incorrect, check the
test points given in Table 4-16 with an RF Voltmeter
and high impedance probe. When a faulty signal is
encountered, replace the key components indicated and
repeat the Checkout Procedure.
Figure 6-19, 455 kHz
Amplifier/AM Detector Schematic Diagram should be
referred to if additional signal tracing/fault isolation is
necessary.
9.
When the 455 kHz Amplifier/AM Detector has been
repaired and is operating satisfactorily, deenergize the
receiver and disconnect test equipment, if no further
tests are to be performed.
Table 4-16.
Amplifier/AM Detector Fault Isolation Chart.
Test Point
Normal Signal
Key Components
Comments
Ql-1
12 mV
at
455 kHz
Ql, CR1, LI
No Modulation
Q2-1
19 mV
at
455 kHz
Q2, CR2, L2, R7
Q3-E
20 mV
at
455 kHz
Q3, L3
Q4-C
300 mV
at
455 kHz
Q4, TI
A4A7-17
90 mV
at
455 kHz
TI
Q5-B
1 V
at
455 kHz
Q5
CR3/L6
3.1 V
at
455 kHz
Q5, L5
Q6-B
4.6 Vdc/1 Vpp - 400 Hz
CR3, Q6
Turn on Modulation.
Use oscilloscope.
A4A7-51
3.8 Vdc/1 Vpp - 400 Hz
Q6, L7
Turn on Modulation.
Use oscilloscope.
4-35
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