Cksm Plug Failure At Power-Up - Tektronix 11A52 Service Manual

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Output Err can fail in Extended Diagnostics without preventing correct calibration. Output Err failure means
that the combined M377 output error and oscilloscope input balance error exceed preset limits. The balance
DAC has enough range to balance some combination of M377 input and BWL errors plus the output error. It is
the calculated maximum balance DAC requirement (i.e., the Balance test) that determines whether the
amplifier will be able to correctly balance under all conditions and not the individual components.
If the oscilloscope is set to bypass new-amplifier-configuration calibration, an amplifier which previously
passed calibration in spite of some Extended Diagnostics being out of range, will fail Self Test at turn on. Self
Test polls the calibration constants obtained during the last calibration, and runs all tests in the Extended
Diagnostics list (except Walking Ones). Any failures, whether fatal to calibration or not, will be reported upon
Self Test. Failures not fatal to calibration do not require service attention, and running an EA (Enhanced
Accuracy) cycle will calibrate the oscilloscope.
If
the message Calibration completed and passed appears at
the top of the screen, calibration is achieved.
After firmware V3.0, the Self Test does not poll Atten Gain, Step Gain, BWL Match, or Output Err.
CKSM Plug Failure at Power-up
If a
1
\amplifier fails Self Test and the message "Cksm Plug" appears in the Routine area, the amplifier
calibration constants have been corrupted. The most common cause of this is turning off the oscilloscope power
during a calibration cycle. This condition may be corrected by pressing EA which initiates a calibration cycle.
When the battery, which is an integral part of and which supplies power to the NVRAM (U801) ultimately
fails, the same Self Test failure will occur at every tum on. Normal operation may be obtained by pressing EA
to initiate a calibration cycle, however, the calibration constants will be lost again when the oscilloscope is
turned off. Replacement of U801 will eliminate the self test failure.
When a "Cksm Probe" failure is indicated, the probe calibration constants residing in the amplifier NVRAM
2xe corrupted. This failure may be cleared simply by removing and reinstalling any readout-encoded probe
(other than a lX probe which, by definition, is not coded).
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NOTE
In Versions 3.6 and greater, the 'CKSM Plug' diagnostic is not run as a power-up self-test. Instead, it
is used to determine whether Enhanced Accuracy status has been retained.
11A52 Extended Service Manual