Check Probecode Stability (Probecodes); Check Signal Path Calconstant Checksum (Cksm Plug) - Tektronix 11A52 Service Manual

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The Address field is not used in this test, and will return zero. If the Actual value returned by the test does not
equal the Expected value from the table above, the test has failed.
Test Failure
The Expected value for this test is 00
hex.
Failure indicates problems with the attenuator shift register ICs
(U850), or with connections between the shift register ICs and the CPU.
Check Probecode Stability (PROBECODES)
The Probecode Stability test checks the probe code voltages to see if they have settled to a stable level within
a given period of time. This routine is actually used as a delay during the self-test period to ensure that the
probecode voltages levels have stabilized before continuing with other self-tests. The Probecode Stability test
normally returns zero in the Actual field; any other value indicates a failure. If the test fails, the bit pattern
reported in the Actual field will represent channels that failed to settle within the allotted time. Bits 0
through 3 of the Actual field represent failures of channels 1 through 4, respectively. The Address field of the
test is not used and will return zero.
Test Failure
The Expected value for this test is 00
hex.
Test failure indicates problems with the analog to digital converter
(ADC) or the voltages fed to the ADC.
Check Signal Path Calconstant Checksum (CKSM PLUG)
The calconstants in the amplifier are protected by a checksum generated after a calibration cycle, or after the
amplifier calconstants are modified using the CAL CONST_SET command. The calconstant checksum helps the
amplifier detect the corruption of calconstants caused by external problems such as alpha-particle hits, bad
NVRAM battery, power failure during the NVRAM kernel test, or other failures.
The signal path calconstant checksum test runs a checksum algorithm on calconstants related to the signal path
of the amplifier (not including probes) and compares the calculated checksum with the checksum stored (with
calconstants) in NVRAM. If the calculated checksum does not match the stored checksum, it indicates that the
calconstants (or the checksum) have changed.
Note that setting the calconstants to factory defaults will not cause a new calconstant checksum to be generated
for the factory default calconstants. The signal path calconstant checksum test will continue to fail until the
amplifier is either run through a calibration cycle, or the CAL CONST_SET command is used to force a new
calconstant checksum to be generated. The Address field is not used in this test, and is zero. The Actual field
will be zero if the checksum was correct, and nonzero (with no significance to the value) if the checksum was
incorrect.
11A52 Extended Service Manual 4-7