362 Chapter7
General Troubleshooting
Block Diagram Description
Triggering
The spectrum analyzer has five trigger modes: free run, single,
external, video, and line. The free run and single trigger signal comes
from the 1 MHz ADC clock. The line trigger signal comes from the A6
power supply. Video triggering originates from the A3 video filter buffer
circuit. External triggering requires either a high or low TTL logic level
as determined by the setting of the trigger polarity function. The
external trigger signal is received from a rear panel BNC connector. A
DAC in the trigger circuit sets the video trigger level. The trigger
circuit is responsible for setting HSCAN high.
Controller Section
The controller section includes the A2 controller assembly and A19
GPIB assembly. The battery on the rear panel provides battery backup
for state and trace storage.
In 8564EC and 8565EC instruments the A2 contains the CPU, RAM,
ROM, the display ASM, Fast ADC circuitry, GPIB interface, control,
frequency counter, display RAM, option module interface, and EEROM.
The A19 GPIB is a mechanical interface between the standard GPIB
connector and the ribbon cable connector on the A2 controller assembly.
All four RAM ICs are battery-backed. The battery-backed RAM stores
trace information (two display memory RAMs) and spectrum analyzer
state information (two program RAMs). A total of eight traces and ten
states may be stored. Typical battery life is five years with the lithium
battery. Trace and state information may be retained for up to
30 minutes with a dead battery and power turned off. This is due to the
very low data retention current of the RAM.
EEROM
The EEROM stores important amplitude-related correction data. This
includes data for LO distribution amplifier DACs, preselector slope and
offset DACs, RF gain DACs (flatness correction), and preselector peak
DAC. The spectrum analyzer serial number, model number, and
installed options are also stored in EEROM.
Firmware The spectrum analyzer firmware reads the model number
and installed options from the EEROM to determine how to respond to
certain keystrokes.
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