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M aintenance— 2440 S ervice
DIAGNOSTICS AND INTERNAL CALIBRATION ROUTINES
INTRODUCTION
This subsection describes function and operation of the
internal diagnostics and calibration routines. Where calibra
tion routines make use of internal diagnostics, the interac
tion is explained. Status and other messages resulting
from running the diagnostics or calibration routines are
also detailed, and special conditions, such as the impact of
power loss while certain diagnostic or calibration routines
are running, are discussed.
In addition to the diagnostics and calibration routines,
the Special Diagnostic menu and the features it accesses
are also covered, including how they relate to the internal
diagnostic routines. Information on how to run the diag
nostics from the GPIB interface is included, followed by a
table
of
Diagnostic/Troubleshooting
procedures
for
this instrument.
OVERVIEW
This instrument supports two types of internal diagnos
tic tests and calibration routines. Self Calibration (SELF
CAL) and Extended Calibration (EXT CAL) calibrate the
analog subsystems of the scope to meet specified perfor
mance requirements. Any detected faults in the control
system and/or in the self-calibrating hardware result in a
“FAIL” message that labels the failed calibration type
(SELF or EXT). Both SELF and EXT CAL make use of
some of the diagnostic routines that comprise the
Extended Diagnostics.
Self Diagnostics (SELF DIAG) and Extended Diagnos
tics (EXT DIAG) are the two types of diagnostic routines
used to detect and isolate system operation faults in this
instrument. The tests are based on a multi-level scheme.
First the highest system level, the kernel, is tested, and
then lower-level subsystems are progressively tested.
Each lower-level subsystem tested follows a higher-level
system that tested good. When the SELF DIAG detect a
system fault, they isolate the fault to one of the upper-
level subsystems immediately above the kernel.
EXT
DIAG can then be used to isolate the failure to lower-level
subsystems and to test those subsystems, down to the
lowest possible level.
In addition to the calibration and diagnostic routines
just mentioned, there are the “Special” diagnostic features,
useful for instrument troubleshooting, and Service Rou
tines which are usually used with the Extended Diagnos
tics to isolate instrument failures.
CALIBRATION ROUTINES
SELF C A L
When the system runs the Self-Calibration routine, it
generates test voltages to the Peak Detectors via the Cal
Amplifier and DAC system. These voltage are used to set
the gains, offsets and/or centering, and balance of the
CCD Samplers, Peak Detectors, and Preamplifiers. The
system uses iterative calculations to modify these voltages
until converged solutions are reached; these converged
solutions become the calibration constants stored in
NVRAM
(nonvolatile
RAM)
and
are
used
to
maintain calibration.
When SELF CAL is run, there is some interaction
between the calibration routines for the different analog
circuits calibrated. This interaction is minimized by using
calibration constants obtained from the last SELF CAL run
as starting values for calculating the new calibration con
stants when a new SELF CAL is run. If you are running a
SELF CAL after a “COLD STA R T’ (see ‘ SPECIAL Rou
tines” in this section), the previous calibration constants
are discarded; therefore, the SELF CAL tests are done
twice to assure a converged solution. (The time required to
perform the SELF CAL procedure from a COLD START is,
therefore, obviously longer than the normal SELF CAL.)
SELF CAL can be run from the front panel using the
EXTENDED FUNCTIONS menu or by the GPIB routines
for automatically calibrating the internal analog systems.
SELF CAL routines take about 10 seconds and calibrate
most of the analog system. A SELF CAL may be per
formed by the user at any time (scope should be warmed
up). Recommended times are when the ambient operating
temperature changes by a significant amount since the
last SELF CAL was run (see Level 7000-9000 Tests under
“Diagnostic Test and Calibration Failures”) and before a
measurement is made which requires the highest possible
level of accuracy.
6 -2 5
Summary of Contents for 2440
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