Fm/Cw/Ssb Detector Fault Isolation Chart - Watkins-Johnson Company WJ-8718-19/FE Instruction Manual

WJ-BYlB-lS/fE Hr K.HULJVLK
MAINTENANCE
1. Deenergize the receiver.
2. Remove PC board A4A7. Place PC board A4A9 on an
extender.
3. Connect the Oscilloscope Vertical Input to A4XA9 pin
57 using a short coaxial cable with clip leads on one
end. Connect cable shield to the IF Motherboard
ground planen
4. Connect the Signal Generator RF output to A4XA9 pin
13 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 -33 dBm. Set the Generator for FM
Modulation at 400 Hz and 4.8 kHz deviation.
5. Energize the receiver and select the FM Mode. The
Oscilloscope should display a level of > 1 V p-p at 400
Hz. The waveform should be a clean sine wave.
8. If the signal in step 5 is incorrect, check the test
points given in Table 4-20 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 6-20,
FM/CW/SSB Detector. Schematic Diagram should be
referred to if additional signal tracing/fault isolation is
necessary.
9. When the FM/CW/SSB Detector has been repaired and is
operating satisfactorily, deenergize the receiver and
disconnect test equipment, if no further tests are to be
performed.
Table 4-17. FM/CW/SSB Detector Fault Isolation Chart.
Test Point
U2-8
U3-5
A4A9-57
Ul-5
U3-3
A4A9-57
Normal Signal
200 mV at 455 kHz
4 Vpp at 400 Hz
0.5 Vpp at 400 Hz
2 V at 455 kHz
4 Vpp at 400 Hz
1 Vpp at 400 Hz
Key Components
Check BFO
U2, Q3, Q4
U3
Ul, Ql, Q2
CR1, CR2, TI
U3
Comments
Select CW Mode
Select CW Mode
Use oscilloscope
Select CW Mode
Use oscilloscope
Select FM Mode
Turn on FM Modulation.
Use Oscilloscope.
Turn on FM Modulation.
Use Oscilloscope.
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