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 When the

component is replaced and power is restored to the rack, the CPU will become synchronized with the current active unit and, if Primary will take control.

2.If the failure is in the backup ,systemremove power from the rack containing the failed

component and replace the component.	When	power	is restored to the backup unit it
will become synchronized with the active	unit	and, if	Primary will take control.

The following paragraphs describe how the system can be repaired without interruption of control. The replacement of each replaceable component is described.

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).

Series 90-70 Hot Standby CPU Redundancy User's Guide ± December 1993