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5. If the LO feedthrough amplitude is higher than -5
dBm
(signal will be “clipped” at top of
screen) and signals are low in amplitude, suspect a defective A8 mixer assembly.
6. Perform the steps located in “Control Latch for Band-Switch Driver” in this chapter.
7. Check Al3 second converter mixer diode bias at A14J19 pin 1. The bias voltage should be
between -150 and -800
mVdc.
8. Troubleshoot the signal path. Refer to the power levels listed on Figure 12-8, HP 85623
RF Section Troubleshooting Block Diagram.
High Band Problems
1. Perform the steps located in “Control Latch for Band-Switch Driver” in this chapter.
2. Troubleshoot the signal path. Refer to the power levels listed in Figure 12-8, HP 85623 RF
Section Troubleshooting Block Diagram.
Low and High Band Problems
1.
On the HP 85623, press
(PRESET)
and
MALIGEl
LO
&
IF . If any error messages are
displayed, refer to “Error Messages” in Chapter 7, “General Troubleshooting.”
2. Perform the “External Mixer Amplitude Adjustment” procedure in Chapter 2,
“Adjustment Procedures.”
If this adjustment cannot be completed, perform the steps
located in “Third Converter” in this chapter.
3. Perform the “First LO OUTPUT Amplitude” performance test. (Refer to the
HP 8560 E-Series Spectrum Analyzer Calibration Guide or use TAM functional test.)
4. If the performance test fails, perform the “LO Distribution Amplifier Adjustment” located
in Chapter 2, “Adjustment Procedures.”
If the adjustment fails, set the HP 85623 to the
following settings:
Center frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.300
MHz
Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OHz
5. Place the jumper on A14J23 in the TEST position. Remove W38 from the input of A7.
6. Use a power meter or another spectrum analyzer to measure the output of All YTO. The
power should be between
+2
dBm
and
+13
dBm.
7. Reconnect W38 to A7. Place the jumper on A14J23 in the NORM position.
8. If ERR 334 (unlevelled output) is present and the All YTO power output is correct,
the A7 drive circuit may be defective. Refer to “A7 LO Distribution Amplifier” in this
chapter.
9. Troubleshoot the signal path. Refer to the power levels listed on Figure 12-8, HP 85623
RF Section Troubleshooting Block Diagram.
RF Section 12-5