455 Khz Filter Switch Fault Isolation Chart - Watkins-Johnson Company WJ-8718-19/FE Instruction Manual

MAINTENANCE
WJ-8718-19/FE HF RECEIVER
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4. Connect the RF Voltmeter input to A4XA3 pin 57 using
a short coaxial cable with clip leads on one end.
Connect cable shield to the IF Motherboard ground
plane.
5. Connect the Signal Generator RF output to A4XA3
pin 13 using a short coaxial cable with clip leads on
one end. Terminate the generator with a 50 ohm load.
Connect cable shield to the IF Motherboard ground
plane. Set the Generator output frequency to 455 kHz
and output level to -27 dBm.
6. Energize the receiver. The RF Voltmeter should display
a level of 25 mV.
7. Select the 1.0 kHz BW and then the 0.3 kHz BW
positions. The RF Voltmeter should display no less than
20 mV in both BW positions.
8. Check the Test Points given in Table 4-14 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 6-17, 455 kHz Filter Switch Schematic Diagram
should be referred to if additional signal tracing/fault
isolation is necessary.
9. When the 455 kHz Filter Switch has been repaired and
is operating satisfactorily, deenergize the receiver and
disconnect test equipment, if no further tests are to be
performed.
Table 4-14. 455 kHz Filter Switch Fault Isolation Chart.
Test Point
Normal S
ignal
Key Components
Comments
Q5-C
23 mV
at
455
kHz Q5
Select 3.2 kHz BW
Q3-C
27
mV
at
455 kHz Q3
Select 1.0 kHz BW
Q4-B
17 mV at
455 kHz
FL2, Q4
Ql-C
19 mV at
455
kHz
Ql Select 0.3 kHz BW
Q2-B
17 mV at
455 kHz
FU, Q2
A4A3- 57
25 mV
at
455 kHz
Q2, Q4, Q6
3.2 kHz BW
A4A3- 57
20 mV
at
455
kHz Q2, Q4, Q6
1.0, 0.3 kHz BW
4-32