Akai S1000 / S1100 samplers

I recently bought an S-1100 and try to install a 1GB Fujitsu SCSI HD 
inside. When I connect it to the external SCSI connector (with an 
adapter cable) it is recognized but when I connect it at the internal 
connector the S1100 freezes at the message "waiting for hard disk..".
The SCSI ID of the HD is ID5 so that should not be the problem. 
I tried it both with the hd not terminated and with a scsi terminator 
plug at the last SCSI plug on the cable.

I read about SCSI cards sometimes being defective, could this also be 
the case with only the internal SCSI connector? Cause the external 
works. Or is the internal more picky about the harddisk being used?

Thanks a lot for any help!!

All the best, Boudewijn