58 Chapter 2
Overall Troubleshooting
Troubleshooting Using Front Panel Keys
Using Service Features
NOTE When the Service key is pressed, a password prompt will appear. Enter
-49, Enter to access the Service Mode.
Press
Service again to access the following keys:
Flatness
Bandlock
50 MHz Osc
LO Null
Noise Source
Diagnostics
1st LO State
Flatness
The instrument default is
Flatness On, and this causes the instrument
to function as follows:
The System Variable Gain circuit on the A10 3
rd
Converter assembly
provides gain to compensate for the frequency response (roll-off) of the
instrument. The amount of gain needed for a given frequency point is
determined by the flatness correction values stored in the instrument
memory during the flatness adjustment procedure. There are
thousands of correction points since additional corrections must be
made for the optional Preamp and the Digital Demod Hardware states.
The Variable Gain circuit also sets the level of the internal 50 MHz
calibrator.
The System Variable Gain circuit cannot remove the ripple component
of the frequency response. This ripple is removed with video shift on the
A7 Digital IF assembly.
When
Flatness is turned Off, the System Variable Gain is fixed at the
50 MHz setting. The video shift is turned off. The result is that the
instrument displays the uncorrected frequency response of the
hardware. Repair technicians can then compare the uncorrected
hardware performance to the corrected performance and determine if a
problem is caused by hardware, an adjustment error, or bad correction
values.
Band Lock
The
Band Lock key tunes the first LO and sets the system gains
according to the particular band that is selected. This process is needed
to force the instrument to be tuned to the desired band in the frequency
overlap regions.
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