AT&T System 25 - Manual (Page 188)

MAINTENANCE
Common Control Problems
Common Control circuitry is difficult to troubleshoot. The system must be
powered down before any of these CPs are replaced. Before powering the
system down, save translations to tape (see “Using the Digital Tape Unit”).
Other repair procedures may also require the system to be powered down.
After removing a suspected faulty CP, do the following:
●
Visually inspect the CP. If a problem is identified, attach a note to
the CP identifying the problem.
●
Attach any error reports that may apply.
●
Visually inspect the cabinet backplane.
After the suspected faulty CP has been replaced, the system can be powered
up. When the CPU/Memory CP is replaced, all historical data is lost. The
system will then have to be restored from the tape backup unit with the latest
copy of the system’s translations.
If no tape exists, the system has to be
reinitialized.
Multiple errors and off-board errors are more likely to occur in common
control problems than in port problems. Use of the Error Log is imperative
in clearing common control problems.
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