Linear Amplifiers - HP 8560E Service Manual

IF Section
Log Amplifier Assembly (P/O A4)
4. Using the DMM, check the voltage at U503 pin 6.
5. Verify that this level is about −700 mV.
6. Adjust the source amplitude to place the signal at the reference
level.
7. Reduce the input signal level in 10 dB steps, down to −60 dBm, while
noting the voltage displayed on the DMM. The voltage should
increase (become less negative) at a rate of 30 mV for each 10 dB
decrease in input power. Troubleshoot the A4 assembly if the signal
does not decrease properly.
8. Set the spectrum analyzer resolution bandwidth to 100 kHz to place
the wide/narrow filter in narrow mode.
9. Repeat steps 2 through 7.
10.If log fidelity is poor near the bottom of the screen or the 1 MHz
resolution bandwidth is narrow, a fault might exist in the
wide/narrow filter switch. (Refer to function block G of A4 log
amplifier schematic diagram in the
Analyzer Component Level Informatio
a. Monitor voltages on A4U302 pins 1 and 7 while changing the
spectrum analyzer resolution bandwidth from 100 kHz to 300
kHz.
b. If the voltages do not come within a few volts of the +15 V and −15
V supplies, U103 and U302 are suspect.
c. Disconnect the digital multimeter and reconnect W27 to A4J3.
Linear Amplifiers
Refer to function block C of A4 log amplifier schematic diagram (sheet 2
of 4) in the
HP 8560 E-Series Spectrum Analyzer Component Level
n. The Linear Amps consist of two variable gain stages,
Informatio
U201C and U201E as well as the buffer amplifier A4U201B, A4U201D,
and A4Q201. The linear amplifiers provide 0 to 40 dB of IF gain in 10
dB steps. The gain of A4U201C can be increased by 20 dB by turning on
A4CR201 and A4CR210 with the control line LIN_20B. The gain of
A4U201E can be increased by either 10 dB or 20 dB with the control
lines LIN_10 or LIN_20A respectively. The gain can be selected by
setting the spectrum analyzers reference level.
422
HP 8560 E-Series Spectrum
n.) Check this switch as follows:
Chapter 8