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80 Series 90-70 Hot Standby CPU Redundancy User’s Guide – December 1993
GFK-0827
On-Line Repair
With a Hot Standby CPU Redundancy system most system component failures can be
repaired by replacing the failed component while the system is on-line. These on-line
repair procedures are possible because of the role switching capability of the units in the
system. Status of the Primary and Secondary units is determined by observing the
LEDs on the Redundancy Communications Module. There are two basic situations
regarding the active and backup units that you should be aware of when a component
needs to be replaced.
1. If the failure is in the active system, control will switch to the backup system. Power can
then be removed from the rack containing the failed component
2.
Note
If maintenance is to be performed on a unit when that unit is the active
unit in a synchronized system, then control should be switched to the
other unit before powering down. This will allow for an orderly transfer
of control.
After repairing a defective unit:
1. Power-up the CPU rack in STOP mode.
2. Verify that the Remote Ready and Remote Active LEDS are on while in STOP mode.
3. Verify that the Local Ready and Local Active LEDs are on in the Active unit.
4. Put the repaired unit in RUN mode.
Maintaining Parallel Bus Termination
It is important when doing on-line repair to maintain parallel bus termination on the
active unit. This is the reason that the terminated parallel cable (IC697CBL811 or
IC697CBL826) is used, and why the RCM must be the last device on the parallel bus. The
terminated end of the cable may be safely removed from a de-energized RCM. These
terminated cables should be considered an integral part of the unit it terminates.
On-Line Repair Recommendations
It is advised when doing on-line repair to power-off the entire PLC system (of the
suspect unit), including ALL RACKS. Change the suspect part, and power-up in STOP
mode. Verify that the links are operational before switching to RUN (%S bits and RCM
LEDs update in STOP mode).