Linear Amplifiers; Log Amplifier (P/O A4 Assembly) - Agilent Technologies 8564EC Service Manual

IF Section
Log Amplifier (P/O A4 Assembly)
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 8564EC or 8565EC 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 8560 E-Series Spectrum
Analyzer Component Level Information.) Check this switch as
follows:
a. Monitor voltages on A4U302 pins 1 and 7 while changing the
8564EC or 8565EC 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 8560 E-Series Spectrum Analyzer Component Level
Information.
444 Chapter 9