In order to use the S-550 with external SCSI devices, you will need the HD5-IF interface. This was an optional kit that added a 25 pin SCSI port to the S-550. Unfortunately, this kit is no longer available. Up to 4 SCSI devices can be connected to the S-550.

Troubleshooting
The S-550 will search for the SCSI devices that are connected to it as it first starts up. Make sure that your drives are up and running before starting up the S-550. If the system locks up as it is booting, check for the following:

1. Make sure that the cable is completely inserted into the ports.
2. Make sure the SCSI drive is set to an ID other than 7. ID 7 is reserved for the S-550 and can not be changed.
3. Be sure the drive that is last on the SCSI chain is terminated and that the other drives connected in the middle of the SCSI chain are unterminated. Most hard drives use either internal or external DIP switches to change termination and SCSI IDs. If the drive you are using has no termination, you can terminate it with a external termination plug. Usually, external terminators are inserted into the line between the SCSI port and the cable or into the other available SCSI port on the drive.
Make the appropriate changes and then restart the drives and the S-550 in that order. If the S-550 doesn't recognize the drive(s), check the table below to ensure that you are using SCSI devices that are compatible with the S-550.