Watkins-Johnson Company WJ-8718-19/FE Instruction Manual page 186

WJ-8718-19/FE HF RECEIVER MAINTENANCE
4.3.4.16 AGC Amplifier, A4A6, (796175) Testing and Troubleshooting
AGC Testing and Troubleshooting includes a checkout procedure and fault
isolation information. A Signal Generator and a Digital Voltmeter (Table 4-1) are
required to perform the tests outlined belown
Perform the following procedure in the sequence given. If any specified
result is not obtained, refer to Table 4-15 for fault isolation.
1. Deenergize the receiver.
2. Remove PC boards A4A3, and A4A10.
3. Set the receiver Gain Mode to Fast AGC and Meter
switch to Line Audio.
4. Connect the Digital Voltmeter input to A4XA6 pin 47
using a short cable with clip leads on one end.
Connect the common lead to the IF Motherboard ground
plane. Set the Digital Voltmeter to the 20 Vdc range.
5. Connect the Signal Generator 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. Set the Generator output frequency to 455 kHz
and output level to -40 dBm.
6. Energize the receiver. The Digital Voltmeter should
indicate -3.5 Vdc.
8. If the signal in step 5 is incorrect, check the test
points given in Table 4-15 with an oscilloscope and high
impedance probe. When a faulty signal is encountered,
replace the key components indicated and repeat the
Checkout Procedure. Figure 6-18, AGC Schematic
Diagram should be referred to if additional signal
tracing/fault isolation is necessary.
7. Select the receiver MAN Gain Mode. Adjust the RF
Gain control until the Digital Voltmeter indicates the
same level indicated in step 7.
8. Select the Fast AGC Mode.
9. Connect the Digital Voltmeter clip lead to A4XA6 pin
19. The Voltmeter should indicate +0.7 Vdcn
10. Connect the Digital Voltmeter clip lead to A4XA6 pin
41. The Voltmeter should indicate -3.0 Vdc.
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