Audio Amplifier Fault Isolation Chart - Watkins-Johnson Company WJ-8718-19/FE Instruction Manual

WJ-8718-19/FE HF RECEIVER
MAINTENANCE
Table 4-18. Audio Amplifier Fault Isolation Chart
Test Point Normal
Sig nal
Key Components
Comments
Ql-D 0.45 Vpp
at 400 Hz
Ql, Ul, CR1
Select AM Mode
Ul-14
0.3 Vpp
at
400 Hz
Ul
C8, R18
300 mVpp
at 400 Hz
Line Audio Control
U2-2, 13
15 Vpp
at 400 Hz U2
R7, R8 20 mVpp
at
400 Hz Phone Level Control
Tl-5
7 Vpp
at 400 Hz
Ul, Tl
U2-14 +22 Vdc Q2
4.3.4.20 1st LP Synthesizer, A5A1, (p/o 791630) Testing and Troubleshooting
1st LO Synthesizer Testing and Troubleshooting includes a checkout
procedure and fault isolation. 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 4-19, 4-20 and 4-21 for fault isolation.
1. Deenergize the receiver.
2. Disconnect connector from A1J2.
3. Connect the Frequency Counter to A1J1.
4. Energize the receiver and tune it to 00.00000 MHz. The
Frequency Counter should indicate 42.91 MHz.
5. Rotate the tuning knob counterclockwise and tune
receiver to 29.99999 MHz. The Frequency Counter
should indicate 72.90 MHz.
6. Disconnect the Frequency Counter and connect the RF
Volt meter and 50 ohm Probe to A1J1. The Voltmeter
should indicate +20 dBm +/- 2dBm.
7. If the signals in steps 4-6 are correct, you may
deenergize the receiver and remove all test equipment
unless further testing is desired.
8. If the signals in steps 4-6 are incorrect, the following
tables may be used as fault isolating aids for
troubleshooting and repairing the 1st LO.
9. VCO Band Select Circuitry - Table 4-19 below checks
for proper operation of U13, diodes CR8 through CR10,
and Ql through Q3, while dialing different frequencies
on the front panel.
4-39