1St Lo/Vco Fault Isolation Chart - Watkins-Johnson Company WJ-8718-19/FE Instruction Manual

WJ-8718-19/FE HF RECEIVER
MAINTENANCE
13. 1st LO VCO - The 1st LO VCO is located on the 1st
and 3rd LO PC board. Table 4-21 below checks for
proper operation of the VCO and -buffer amplifiers. Set
the receiver to a tuned frequency of 29.99999 MHz and
use an oscilloscope with low capacitance probe to check
the tests points indicated. Diodes CR1-CR3 should be
checked with an ohmmeter for continuity.
Table 4-21. 1st LO/VCO Fault Isolation Chart.
Test Point
Normal Signal
Key Components
Comments
Ql-2 1 Vpp @ 291.60 MHz
Ql, CR4, CR1-CR3
CR1-CR3 conduct
Q2-C
2 Vpp
Q2
Q3.-C
10 Vpp
Q3
Ul-3
5 Vpp @ 72.90 MHz
Ul, Q4 Divide by 4
El
6 Vpp
Q5, Q7 1st LO output
14,
When the 1st LO has been repaired and is operating satisfactorily,
deenergize the receiver and disconnect test equipment, if no further
tests are to be performed.
4.3.4.21 2nd LO Synthesizer, A5A2, (791601) Testing and Troubleshooting
2nd LO Synthesizer Testing and Troubleshooting includes a checkout
procedure and fault isolation information. A Frequency Counter, wideband Oscilloscope,
and RF Voltmeter (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 Tables 4-22, 4-23 and 4-24 for fault isolation.
1. Deenergize the receiver.
2. Disconnect connector P13 from A5A2XB15/16.
3. Connect the Frequency Counter to TP13.
4. Energize the receiver and tune to 00.00000 MHz. The
Frequency Counter should indicate 32.21 MHz.
5. Tune the receiver to 00.00999 MHz. The Frequency
Counter should indicate 32.20001 MHz.
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