The first and last device in a chain of SCSI devices must be terminated. 
This is accomplished either with a jumper or SCSI terminator resistors. 
The first device, the adapter card, usually is self-terminating. The last 
device must be terminated if the card does not do it automatically.

If the Ricoh 1420c is the last or the only device on the SCSI chain, it 
must be terminated.  Termination is set by inserting the two resistor packs.
With the drive face up, the lettering on the resistors should appear 
face-down (if they're in face up, the drive won't be recognized properly.)

(Consult the documentation on how to terminate other SCSI devices.)