AT&T 3B2 Maintenance Reference Manual page 313

Appendix B: Using the Diagnostic Monitor
Introduction
The set of diagnostics available from the 3B computer hard disk diagnose the system board,
the attached disks, and the peripheral cards inserted into the backplane. Since this document
deals only with repair at the subassembly level, failure of any of the system board diagnostics,
except for the floppy and hard disk (and possibly NVRAM) phases, indicate that the system
board must be replaced. Failure of the floppy and hard disk diagnostics could result from
problems in the drives themselves. NVRAM failures could be caused by a defective battery.
Failure of any phases relating to a peripheral card requires replacement of that card to fix the
problem.
It is possible that a defective 1/0 backplane could cause peripheral card or system board
failures; however, the backplane has a long mean time between failure (MTBF).
NOTE: Although diagnostics should detect at least 80 percent of system faults, diagnostic
results are valid only if the diagnostic code is not corrupted. If a machine exhibits problems,
the results cannot be guaranteed using the diagnostics resident on the hard disk. Use of a
known good bootable diagnostics diskette, such as the 3B2 Maintenance Utilities, is
recommended to ensure valid diagnostic results.
Using the Diagnostic Monitor B-1