Agilent Technologies 8564EC, Service Manual

Page: 317 / 512

Chapter 8 407
ADC/Interface Section
A3 Assembly Control Circuits
A3 Assembly Control Circuits
A digital control problem will cause the following three steps to fail:
1. On the spectrum analyzer, press
AMPLITUDE
,
ATTEN MAN
, 6, 0, and
dB
.
2. A click should be heard after pressing dB in step 1, unless ATTEN
was previously set to 60 dB.
3. Press 1, 0, and
dB
. Another click should be heard. If no clicks were
heard, but the ATTEN value displayed on the CRT changed, the
digital control signals are not operating properly.
Analog Bus Drivers
Refer to function block N of A3 Interface Assembly Schematic Diagram
(sheet 4 of 6) in the 8560 E-Series Spectrum Analyzer Component Level
Information.
1. Press
PRESET
on the spectrum analyzer, and set the controls as
follows:
Span ................................................................................. 0 Hz
Trigger .......................................................................... Single
2. Monitor A3U401 pin 3 (LRF_STB) with an oscilloscope or logic
probe. This is the strobe for the A15 RF Assembly.
3. Press
AUX CTRL
and
REAR PANEL
and check that pulses occur when
toggling between
10 MHz INT
and
10 MHz EXT
.
4. Monitor U401 pin 5 (LFC_STB) with an oscilloscope or logic probe.
This is the strobe for the A14 frequency control assembly.
5. Press
AMPLITUDE
and check that pulses occur when toggling
between
ATTEN
settings of 10 and 20 dB.
6. Monitor U401 pin 7 (LIF_STB) with an oscilloscope or logic probe.
This is the strobe for the A5 IF assembly.
7. Press
AMPLITUDE
and check that pulses occur when toggling
between
REF LVL
settings of
−
10 dBm and
−
20 dBm.
8. Monitor U401 pin 9 (LLOG_STB) with an oscilloscope or logic probe.
This is the strobe for the log amplifier on the A4 assembly.
9. Press
AMPLITUDE
and check that pulses occur when toggling
between
LINEAR
and
LOG dB/DIV
.
10.To check the Address and Data Lines, place a jumper from A3TP1
and A3TP2 to A3U406 pin 20 (+5 V).