Watkins-Johnson Company WJ-8718-19/FE Instruction Manual page 187

MAINTENANCE
WJ-8718-19/FE HF RECEIVER
11. 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.
12. When the AGC has been repaired and is operating
satisfactorily, deenergize the receiver and disconnect
test equipment, if no further tests are to be performed.
Table 4-15. AGC Fau]
t Isolation Chart.
Test Point Normal Signal
Key Components
Comments
A4A6-51
+3.2 Vdc
Check A4A7
AGC Mode
Ql-E
+2.7 Vdc
Ql
Ul-1
+2.7 Vdc
Ul
Q2-C
+0.13 Vdc
CR9, Q2, Q6
U2-7
-6.6 Vdc
U2
Ul-14
-3.5 Vdc
Ul
!
U2-10
-0.06 Vdc
Q5
U2-8
-0.32 Vdc
U2
U2-1
+1.07 Vdc
U2
4.3.4.17 455 kHz Amp./AM Detectoi •, A4A7, (726002) Testing and Troubleshooting
i
455 kHz AmplifieroAM Detector Testing and Troubleshooting includes a
checkout procedure and fault isolation information. A Signal Generator, an RF
Voltmeter and 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 4-16 for fault isolation.
1. Deenergize the receiver.
2. Remove PC board A4A3. Place PC board A4A7 on an
extender.
3.
4-34
Connect the RF Voltmeter Input to A4XA7 pin 17 using
[a short coaxial cable with clip leads on one end.
Connect cable shield to the IF Motherboard ground
plane.