Look here for information about the CHECK symbolic FRU.

If the attached device is an external device, do the following before exchanging any parts:

1. Ensure that the device is powered on.
2. Is there a SCSI interface between the IOP/IOA and the device?
   • No: Continue with the next step.
   • Yes: Perform the following:
     • If an interposer is required, make sure that it is connected between the I/O processor and the SCSI cable.
     • Ensure that the SCSI cable is seated correctly, and that there are no bent or damaged pins on the SCSI cable.
     • Ensure that a terminating plug is attached to the device end of the SCSI cable.
     • Continue with the next step.
3. Is there a Fibre Channel interface between the IOP/IOA and the device?
   • No: Continue with the next step.
   • Yes: Perform the following:
     • Verify that any hub or gateway devices are powered on.
     • Verify that the Fibre Channel cable is correctly connected to the ports.
     • If a cleaning kit is available, clean the Fibre Channel cable connectors.
     • Continue with the next step.
4. Perform the verification procedures which are located in the service guide for the system unit to see if the problem was corrected.