TROUBLESHOOTING AND REPAIR
DIGITAL CONTROLLER
CALIBRATION/COMPENSATION MEMORY 6B-22.
The integrity of the calibration/compensation data is vital to the performance of the
instrument. The use of redundant data storage allows the system to recover even if
some of the data has been corrupted.
There are 11 calibration/compensation data segments:
Attenuator
Coarse Loop Compensation
Coarse Loop Steering
Output
Sub-Synthesizer
Sum Loop Compensation
Sum Loop steering
AM Calibration
FM Calibration
RF Level Calibration
Reference Oscillator calibration.
Two identical copies of each data segment are maintained in two separate ICs on the
Controller PCA. One copy is stored in the EEPROM, and the other copy is stored in
the battery-backed RAM. If the power fails while either version is being updated, the
other is still valid.
Calibration/Compensation Memory Status 6B-23.
Whenever the self-tests are performed, the checksums are verified for each data
segment in the EEPROM and in the battery-backed RAM. In addition, each
checksum is compared to the corresponding checksum in the redundant data block. If
one checksum is valid and the other is invalid, the valid copy is used. If both copies
have invalid checksums, overrange/uncal status code 250 is set, and the STATUS
annunciator is flashed.
If any of the checksums fail, self-test status code 302 is reported. Special function 04
displays a list of codes that specify which checksums failed. The list can be scrolled by
pressing the key. If all checksums are valid, the code 00 is displayed. Refer to
Appendix E for a complete list of the checksum status codes.
The most likely failure mode would either be a defective EEPROM or battery-backed
RAM IC that would show failures of all the checksum error codes for that IC. Replace
the defective IC, and refer to "Repairing Calibration/Compensation Memory
Checksum Errors" later in Section 6B.
In addition to checksum error codes, there are codes that indicate when the checksums
are valid, but a byte-by-byte comparison of the data segments reveals that they are
different. This unusual condition is likely to occur only if one of the two calibration/
compensation memory ICs have been swapped between controller boards. Although
this situation rarely occurs, it is important to detect the condition so corrective action
can be taken. The data comparison codes are included with the checksum status codes
in Appendix E.
6B-8
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