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MAINTENANCE
WJ-8718-19/FE HF RECEIVER
Table 4-25.
3rd LO Fault Isolation Chart.
Test Point
Normal Signal
Key Components
Comments
Q8-E
2 Vpp @ 11.155 MHz
Q8, CR7
VCO Circuit
U21-12
3 V peak
Q9, Q10
U21-11
3 V peak @ 50 kHz
Time Base
U22-11
3 V peak @ 5 kHz
U21, Time Base
Divide by 2
U22-8
+3 Vdc
U21, U22
4.3.4.23
BFO Synthesizer, A5A3, (791576) Testing and Troubleshooting
BFO Synthesizer Testing and Troubleshooting includes a checkout
procedure and fault isolation information.
A Frequency Counter and wideband
Oscilloscope (Table 4-1) are required to perform the tests outlined below.
Perform the following procedure in the sequence given. If any specified
result is not obtained, refer to Table 4-26 for fault isolation.
4-44
1.
2.
3.
4.
5.
6.
7.
8.
Deenergize the receiver.
Disconnect connector A4W13P18 from A4XA8-17/19.
Connect the Frequency Counter to W13P18.
Energize the receiver and select CW Mode.
Set the
BFO offset to +0.0 kHz.
The Frequency Counter should
read 455.000 kHz.
Set the BFO Offset first to +8.0 kHz and then to -8.0
kHz.
The Frequency Counter should read 463.999 kHz
and 446.999 kHz respectively.
Disconnect the Frequency Counter and reconnect
A4W13P18 to A4XA8-17/19.
Connect the Oscilloscope input to A4TP15 using a
shielded cable with clip leads on one end.
Connect
cable shield to the IF Motherboard ground plane.
The
Oscilloscope should display a level of >120 mV p-p at
446.999 kHz.
If the signal in step 5 is incorrect, check the test
points given in Table 4-26 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 6-27, BFO
Schematic Diagram should be referred to if additional
signal tracing/fault isolation is necessary.
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